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Charting and Navigation / Cartographie marine et navigation

12 IndexContents / Matières Session / Séance Authors / Auteurs

Section 12

Charting and NavigationCartographie marine et navigation

Electronic Navigational Charting around Australia:Finally, we get to the cartographic production bit!Ronald A. Furness

The Cartographic Generalization of Soundings on Chartby Artificial Neural Network TechniquesJia Yao Wang, Zhen Tian

Performance Measurement of Combined Versus SeparateRadar and Electronic Chart DisplaysDon C. Donderi, Sharon McFadden

The Challenges of Production of ENC Cells and Paper Chartsfrom one Common DatabaseTiina Tuurnala, Ismo Laitakari

An expert system approach for the design and composition of nautical chartsLysandros Tsoulos, Konstantinos Stefanakis

Croatian State Boundary at the Adriatic SeaIvka Tunjic, Miljenko Lapaine

Production of Thematic Nautical Charts and Handbooksfor the Sea Area of the Eastern Adriatic CoastSlavko Horvat, Zeljko Zeleznjak, Tea Duplancic

The use of global mathematical models in the cartography of marine sandbanksTom Vande Wiele

Making practical and effective electronic aeronautical chartsSonia Rivest, Rupert Brooks, Bob Johnson

Ottawa ICA / ACI 1999 - Proceedings / Actes

12 IndexContents / Matières Session / Séance Authors / Auteurs

Environmental Mapping of Russia’s Seas Using GISI. Suetova and L. Ushakova

Airborne remote sensing for water quality mappingon the coastal zone of Abruzzo (Italy)Claudio Conese, Marco Benvenuti, Paola Grande


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Session / Séance 02-B

Electronic Navigational Charting around Australia:Finally, we get to the cartographic production bit!

Ronald A. FurnessAustralian Hydrographic Office8 Station Street, WOLLONGONG 2500, [email protected]

Abstract

The paper (and presentation) will address the cartographic challenges presently being grappled with and metby the Australian Hydrographic Office’s (AHO) cartographers as they work to provide mariners with the firstauthorised and thus, government backed, electronic navigational chart (ENC) database of the inner shippingroute through Australia’s Great Barrier Reef. The title reflects a certain personal level of frustration with thetime it has taken the world’s hydrographic community to get down to the process of compiling official ENCs. Itwill place the Australian experiences in context and discuss some of the cartographic production issues thathave arisen.

Background

The last decade or so has been a thrilling period in the development of nautical charting around the globe. Thistruly international activity has seen the development of electronic charts to the point where they will soon,routinely, deliver a range of capabilities suited for use on a variety of ingenious programmed devices andapplications. Electronic charts promise both improvements in productivity and increased safety margins to thenavigation task of vessels at sea. However, progress has not been without its challenges! Government agen-cies and private commercial concerns around the world have cooperated, competed, fought, argued, createdand generally excelled to bring electronic charting to fruition.

The 1990s have been a decade of concerted activity – some of it cooperative and some competitive. This hasresulted in international standards for electronic charting which promise to deliver to mariners authorisedelectronic charts of the highest standard. This is supported by the delivery to the market of complementarysystems which provide dynamic and real-time navigational capability to the ship’s master, navigator, regulator,safety authority and ship’s owners and crews simultaneously. Meanwhile, many commercial companies havepushed ahead to market, often brilliantly designed, navigational applications for viewing and integrating elec-tronic charts with onboard ship sensors, such as the Global Positioning System (GPS). The result is that themarket will be soon awash with products of various detail, quality, capability and theme.

The database design for official electronic charts has been nothing short of brilliant in this author’s view – andcartographers have been to the fore on the decade long, tortuous development road. The design of object-oriented models of reality – sheer genius!

Cartographic communication theory has withstood the acid test in perception laboratories as screen-basedpresentation and symbolisation issues relating to the presentation of charting graphics have been all but re-solved. Yet we marine cartographers are only just in the position to start to be able to grapple with productioncartography issues. “That’s tomorrow’s problem!” we have been saying, but tomorrow has already passed.


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The promises of increases in safety margins are so attractive and necessary that the market for electronic chartsand systems is increasing apace. Government agencies and commercial organisations are now tussling todefine their roles and their positions in a market hungry for electronic chart technology, yet some are oftenoblivious or unwilling to acknowledge any potential shortcomings.

Realisation of the potential increases in safety margins demands the highest quality and integrity of data in theelectronic digital chart. In the view of this author, they will only be obtained through reappraisal of the basictenets of cartographic professionalism. Compilation of electronic charts must ultimately rest on a full carto-graphic assessment of the best fundamental data available. A simple transference of existing, single productfocussed cartography into the object oriented data models which underpin electronic navigational charts isinadequate, notwithstanding the fact that the exigencies of business dictate “acceptable” short-term alterna-tives, such as scanned or vectorised paper charts. The whole process is presently testing the professional skillsof the cartographers of the Australian Hydrographic Office as it orients its future chart production capabilitytowards delivery of ENCs to the mariner.

The Australian Context

Consider if you will a relatively remote conti-nent, approximately the size of the United Statesand with a continental shelf of similar area. Thiscontinent, Australia, has a population which isapproximately 18 millions. In order for Australiato meet its international charting obligations itneeds to be clever and to exploit technology tothe hilt. Those technologies about to be deliv-ered to its new state-of-the-art, purpose built,hydrographic survey ships and Laser AirborneDepth Sounder have been world leaders and stillAustralia struggles, like many other majorhydrographic nations, to meet its obligations tomodernise its nautical charts and deliver ENC.Diagram 1 indicates that much of Australia’smaritime area is not adequately surveyed to modern standards. The dark areas are considered adequate. Thefaintly shaded area represents the continental shelf. A brief perusal of this diagram will alert the reader to thefact that, for the foreseeable future, the Australian marine cartographer will be forced to meld together dispa-rate data sets and this will impact on methodologies for the immediate future. It is clearly some time off beforeAustralia will have a complete ENC based totally on full bottom coverage digital data.

A Brief History of Charting in Australia

The Australian Hydrographic Office (AHO) has been a traditional charting agency until relatively recent times,delivering to mariners authorised paper nautical charts. In the mid-1980s Australia embarked on a program ofmodernisation which continues today as it transits from a single product deliverer (paper charts) towardsbecoming a modern hydrographic information supplier. The earlier computer aided techniques used in theAHO were limited and limiting in that they sought to assist chart production by replicating paper chart produc-tion methodologies. The main limiting factor in the 1970s and 1980s was technology of course; screens,

Diagram 1


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plotters, digital data collection, positioning; but nevertheless, most of the main ideas were taking shape at thattime for developing ultimate ENCs.

The AHO converted all of its charts to a raster scanned medium and routinely delivers charts in this form tomariners within a product regime that has mastered the updating requirements of the charts. The AustralianSeafarer® service was introduced in 1997. Seafarer® is a fully electronic chart service providing digital repro-ductions of the official Australian paper charts in a raster format. It is suitable for use in a wide range ofmaritime applications, from fully integrated bridge systems to stand-alone PC based Electronic Charting Sys-tems (ENC). An integral part of the product is an update service, which provides the latest new editions andNotices to Mariners updates on a CD that automatically updates the charts. The product has received a numberof prestigious awards.

However, the market clearly wants electronic navigation charts of vector format for use in the now availableECDIS systems. The main limiting factor on all hydrographic offices, but especially the AHO, is the lack ofavailable digital data. The AHO has embarked on a major capital investment which will see its data in digitalform within about three years (known as Project SEA 1430) but in the interim must seek to find ways ofbringing nationally authorised ENCs to the market sooner than that. Since 1998 it has been clear that, for theforeseeable future, ECDIS systems will be multi fuelled. ECDIS is the acronym that means Electronic ChartDisplay and Information System. The authorised national Electronic Navigational Chart is that chart which isspecified to “fuel” the data requirements of ECDIS. The term “multi fuelling” refers to the use in an ECDIS ofvarious authorised charts in different formats. An ECDIS capable of utilising, for example, authorised ENCsand authorised raster charts as well as other publications could be said to be multi-fuelled.

Many countries and private companies, in an effort to deliver ENC products to mariners and having regards tothe paucity of available digital data, have looked to digitising their charts in a way that vectorises them andwhich meet the format specifications of the International Hydrographic Organisation for ENC (S 52, S57).Such an approach is useful in the shorter term and has been adopted in Australia. Willis [1998] has pointed outthat the reasons such data sets of and around major ports were produced in Australia include:

¨ ECDIS testing and demonstration purposes;

¨ development of standard operating procedures for digital data capture;

¨ proof of concept for conversions from Autochart digital files (Autochart and ChartStation are applicationsused by the Australian Hydrographic Office under licence from Hydrographic Sciences Australia Pty. Ltd.);

¨ proof of concept for conversions from S-57 to other formats such as the Digital Nautical Chart (electronicchart to military specification), raster and paper chart;

¨ support of requirements raised within the Department of Defence and by maritime and port authorities inAustralia, and

¨ training of cartographic staff on the newer generation ChartStation application.

Geographical considerations for an Australian ENC in the Great Barrier Reef

Most readers will have heard of the Great Barrier Reef (GBR). Many of you will dream of visiting the GBRand chances are, if you get to see it you will do so by boat or ship. The GBR is the most navigationally complexregion for Australia. The beauty of the Reef is its potential downfall since, although it is hazardous to shipping,shipping is more hazardous to it! The main navigational passage through the GBR is known as The InnerRoute. Diagram 2 illustrates the location of this route with some of the main routes through the Reef to theouter routes and deeper water. The Reef is a magnet for researchers and tourists. Being so environmentallysensitive it attracts world attention and is managed appropriately. The International Maritime Organisation has


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declared the entire GBR a Particularly Sen-sitive Area. The GBR receives special atten-tion from everybody and so also it is the casewith the national charting authority, the AHO.

Compulsory pilotage was introduced in Oc-tober 1991 for ships transiting the GBR In-ner Route and Hydrographers Passage andapplies to all vessels of 70 metres or more inlength as well as all loaded oil tankers, chemi-cal tankers and gas carriers of any length.

Willis [1998] has stated that in response tointernational calls for hydrographic offices toexpedite the release of official ENC data setscompliant with S-57 Edition 3.0, and nationalcalls to improve the state of electronic chart-ing in the Inner Route of the Great BarrierReef, the AHO undertook to produce ENCsof the Torres Strait and Inner Route. At thetime of writing (early March 1999) the firstcells from Weipa in the Gulf of Carpentariato the western approaches to Torres Strait areready for trialling and demonstration. It isanticipated that they will be so used by AHOstaff and ships’ crew on a large commercialvessel, River Boyne, from March 1999. Pro-duction effort progresses cells through TorresStrait and down to the Queensland port ofGladstone. This undertaking has imposed anumber of significant challenges and questions that needed robust responses [Willis, 1998]:

¨ There was a need to develop a comprehensive data capture specification for the ENC.

¨ Was vectorisation of the existing paper chart the best way to present an ENC?

¨ Could we create an ENC of a long narrow strip of waterway, such as one might capture a river, withoutconverting all the paper charts covering that strip? The Inner Route of the GBR is about 1000 kms long byan average 10 – 20 kms wide.

¨ What compromise could be made in limiting the content outside the Inner Route?

¨ Should more information be included within the Inner Route from source data?

The specifications adopted by Australia within the IHO guidelines for the Inner Route ENC are:

¨ Depth contours at 1 metre intervals in critical areas derived from original source data

¨ Soundings initially only in critical areas

¨ Smaller scale charts to provide a backdrop

¨ High resolution in critical areas

¨ Coverage of the Inner Route strip

¨ Adherence to IHO Specifications and Standard Display requirements

Diagram 2


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Experiences

Paper charts

The processes for the production of paper charts are well known but it serves my purposes to recapitulate somemain aspects of those processes. Hydrographic surveys are carried out to measure the actuality of depth overtime. As a result, the chart making cartographer is faced with the task of melding multiple, disparate data setsof differing age, fidelity, accuracy and quality. These hydrographic data sets have to be interpreted at everystage (having already been interpreted by surveyors and instruments in the first place) and again melded withother disparate data sets: topography, navigation aids, Notices to Mariners, textual data, boundaries informa-tion, pilot information, hydrographic notes from all manner of sources and politico-geographical informationof the widest sense. The task facing the chart-compiling cartographer then, when faced with a blank sheet anda keen mind, is to abstract, extract, interpret, generalise and construct ultimately a cartographic representationof earthly reality. This representation follows specification yet seeks to serve every conceivable mariner whomight seek to go down to that particular part of the sea in a boat or ship.

The cartographer’s painstakingly created palimpsest is eventually affixed in a form that bears printed repro-duction, or these days, computer reproduction and becomes a document that must be maintained forever that itexists as an authorised document. The marine cartographer has been working as an interpreter, as a combina-tive agent. The result of her labours a cartographic representation of reality: a thematically biased chart fixedby its very medium. Fixed in its presentation and fixed in form and use.

Why have I laboured this point? I am endeavouring to set up in the reader’s mind the paradigm in which, untilrecently, marine cartographers working in the area of nautical charts have operated. I will now attempt toexplore the issues raised by the new paradigm for ENC production before drawing my conclusion.

Electronic Navigation Charts

The AHO experiences I have outlined earlier describe what might be seen as a transitioning from traditionalcartographic processes to a more modern process where the cartographer is returning to the original data and isattempting to interpret the data in a way that suits a more objectified presentation. At the same time, theimperatives of technology are impacting on the ability of those in the field to collect more and more new andprecise data. Laser Airborne depth sounders, digital swathe devices and data management systems are alreadypushing the limits of the most powerful graphics machines and smart graphics seem the only way humans canimpose some quality processes on the mass of data collected. So in a sense, the interpretative skills of thehydrographic surveyor have changed. Some might say they have been eroded as the data collection processbecomes more objectified. There’s some merit in this argument and it might be inevitable, but this authordisagrees that complete objective data is presently deliverable to the chart making process.

Hydrographic Offices, including the AHO in particular, have been aware for some time of the need for them toposition themselves to be able to generate ENC, raster and paper charts products from the single moderatedsource data set. They are painfully aware that the data set must be maintained, as must be the products.

So marine cartographers must focus on new ways to present chart information. Paper products have toleratedregional differences in presentation. The dream of a single worldwide ENC coverage and the rigid demands ofcomputer systems required to run these ENC databases mean that myriads of minor differences are intolerable.No longer is the chart compiler able to have some determining role as to how some “feature” might be de-picted, or even how far it might be displaced in position for aesthetic cartographic presentation, but she must befaithful to the “object”, describing it and its relationships precisely. So we are starting to see a shift in carto-graphic thinking here from the subjective to the objective. Subjectively defined graphic has given way toprecisely defined and comprehensively described real world object.


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But what of theoretical objects such as dredged channels? Clearly I do not mean that dredged channels existonly in theory but that their traditional cartographic presentation as features depicts them in a theoretical way.Sharp, precise channels with absolutely level bottoms. Modern data collecting devices soon disabuse one fromthe notion that such preciseness exists in the real world. What is traditionally depicted on charts for dredgedchannels typically is a gazetted limit with a defined (guaranteed) minimum depth and not the precise actualchannel. So where does this leave the marine cartographer grappling to define reality more precisely? Well,clearly still with cartographic objects in a real world. But the example serves to lead into the point about thechanging view of data and the synergy that modern computers unleash for others such as environmentalists,researchers, legislatures, law enforcers, searchers and rescuers, coastal zone managers and so on. This list is byno means exhaustive but illustrates a largely untapped demand for hydrographers’ data. It also serves to makethe point that the marine cartographers’ responsibilities are shifting away from “just” the mariner. As expertinterpreters of the hydrographic and navigational data, cartographers are inexorably repositioning themselvesand their professional role and obligation to society. If you think I am drawing a long bow then consider thescramble for interpretive advice arising from the requirement for nations to define their various offshore zones!

Any cartographer who has worked for a major map or chart-producing agency will be aware of the push forminimising effort for derived mapping. The push continues and is almost there conceptually in the objectoriented marine world. However, the mind processes of the cartographic as she defines objects are at oncespanning all possible uses of that object for a myriad of possible uses. So the mind is moving here from theparticular (THIS scale, THIS use, THIS presentation) to the general (ALL possible scales, ALL possible uses,ALL possible presentations). The mariner, at sea, on a cramped bridge, with terrible visibility, with immenseresponsibility, unstoppable momentum and almost certain dependency on electronics, is interested ultimatelyin a fundamental binary equation – GO or NO GO! The mariner is now able to relate precisely and absolutelyto the real world in real time. A realisation of this must be uppermost in the mind of the cartographer interpret-ing the data in the comfort of an office, particularly when making “decrees” as to issues such as usage, quality,relative accuracy. This is quite a shift in the thinking for most chart makers and requires that they thus developnew paradigms.

The mariner is not able, as we were entreated by Cervantes’ Don Quixote, to “journey all over the universe ina map, without the expense and fatigue of travelling, without suffering the inconveniences of heat, cold,hunger and thirst”. Chart makers must come out from the comfort of their offices and start to experience someof the “heat, cold, hunger and thirst” of the real world as they make their charts. This is starting to happen inAustralia.

One interesting side issue for cartographers is the increase of ephemeral mapping or charting with a concomi-tant decrease in graphic quality. So what! The world now looks at polygon colours and reports rather thanlines and text and presentation of both need to conform with emerging standards if they are going to synergisewith what already has emerged rather than reinvent wheels: chart standards, SGML, HTML, GIF, JPEG,internet etc. No longer is it be productive to argue for hours as to whether a piece of text has rounded ends, isexactly 6.0000000 points in size and 0.0001235 mm thick. Modern cartographers have all but dispensed withthat mind-set and many an eye glass has found its way to the historical artefact shrines of cartography (whichironically still adorn many an entrance to the most progressive mapping and charting enterprises). No longercan cartographers expect their images to remain extant forever though this author admits to a certain feeling ofimmortality to discover that the first chart he ever compiled remains the current Admiralty chart for the par-ticular port.

Another interesting issue for the cartographers engaged in nautical chart production is the increasing use ofdata based information such as lights, buoys, boundaries, text, photographs, attribute management, tomes andon. The actual compilation process is requiring compilers to focus more on the actual bathymetry and theconstruction of bathymetric polygons. When the aim is to include isobaths at metre or sub-metre interval, then


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the subsequent polygonisation is, to say the least, challenging. Overkill? Hardly when increasingly marinersare demanding greater and greater detail and accuracy in order to rationalise their loads to minimum underkeelclearances in critically sensitive areas such as the GBR. The challenges for quality assurance and control areimmense and are being faced as opportunities by the day!

I have already alluded to the expanding horizons for chart data interpreters and, while it might seem trite to doso, I point out that the present IHO specifications have been designed to a large extent from a cartographicperspective. To that extent they are limiting. However, future (decade plus) improvements will ultimately seeprecise interaction between dynamic data (ship’s draught, tidal models, ice edges, weather, for example) andthe databased chart information and tolerances between the GO / NO GO margin will shrink. Thus cartogra-phers need to be far reaching in their present day mind sets.

We face all the time the dilemma between the need for certainty in our specifications and processes and theneed for innovation and flexibility. Notions of multi-fuelling with various data sources, in itself a rational andtransitional option, forces compromise and stifles creativity and innovation.

When marine cartographers deliver a paper chart the medium is very much the message. Rigid and generalisedin presentation, the presentation could be said to conform to the principle that “one size fits all”! The advent ofdigital data separates the medium from the message in that the message to the mariner must come via anelectronic chart system, or ECDIS. This has spawned a number of Faustian relationships between HOs andmanufacturers with no clear lines of demarcation in respective roles. This is clearly part of the developmentconundrum, but as we progress there are signs that the market place is better realising proper roles for author-ised government agencies and the commercial imperatives of system manufacture.

Conclusions

So where does this all leave me given that it’s time to begin to draw my thoughts together?

It leaves me, I believe, arguing a case for a recognition that the cartographic paradigm for marine cartographyis shifting from a more subjective and perhaps narrower professional role to one that is more general, or wider,and more objective in its professionalism. I believe that this modern role is encapsulated in the notionalgeneral description “mapping scientist” of which traditional cartography remains an important part. Such folkwill be required to be more eclectic in their thinking and will be able to project forward as they work to themultiple uses their work will be put. I believe that I have shown that such a role is better descriptive of theessential paradigm shift in production processes that cartographers must undertake if they are to remain at theforefront of delivering geographical interpretations of the real world to modern users of such information.

So in the final instance we have got to the cartographic production bit but need to recognise that the paradigmhas changed already. We need to change as professionals to be in line! As one wit has said, “we are at thebleeding edge”! If that’s the case then the experiences are presently being written in blood, but finally, they arebeing written and we are rising to meet the challengesS!

References

Willis R J, [1998] Towards “AUS ENC ONE”, Proceedings, Institution of Surveyors 39th Australian Surveyors Con-gress, Launceston.


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Session / Séance 02-D

The Cartographic Generalization of Soundings on Chart by ArtificialNeural Network Techniques

Jia Yao WangDept. of Cartography & Geoinformatics, Zhengzhou Institute of Surveying & Mapping66,Mid-Longhai Rd. Zhengzhou, China, 450052E-mail: [email protected]

Zhen TianDept. of Marine Surveying and Mapping,Dalian Naval Academy, Dalian, China, 116018Tel: +86-411-2678355 E-mail: [email protected]

Abstract

As a main part of nautical chart cartographic generalization, the generalization of soundings is also one ofthe bottlenecks in the way of automatic chart generalization. In this article, the design of neural networkgeneralizing soundings was discussed, along with the analysis on the network’s overall structure, the workingmethods, the network factors, learning. To solve the problem of dealing with both the spatial and attributivefactors at the same time in the selection of soundings, a new set of operations is designed based on a practicalproblem-solving model called “Hierarchical Information Structure”. The experimental result is shown upon aprotocol system.

1 Generalization of Soundings on Nautical Chart

Soundings, sometimes called the notation of water depth, are the numeral symbols showing the depth of seawaterfrom depth datum to the bottom of sea, scattering in the sea area on nautical charts. For both the purposes ofmaking it practical and good-looking, soundings on nautical charts are required to form a net of approximatelydiamond-shaped, which means that the generalization of soundings deals synchronously with both spatial (thescattering pattern) and attributive(depth, and more) characteristics of the chart features.

On current Chinese nautical charts, the seabed terrain is shown mainly by soundings, with the assistance ofdepth contours and bottom natures. So the correct and reasonable generalization (selection) of soundings isessential to make a good chart, scientific and helpful to the mariners

1.1 The Requirements of Sounding Selection

1. Soundings which are at the top of a raised under-water area (shoals, rocks, etc.) have the highest priority tobe selected. Generally select the shallower prior to the deeper ones to guarantee the safety of navigation;

2. Then choose the soundings which show the waterways;3. Then choose the soundings which represent the outline of sea bottom the best;4. Choose the other soundings to fulfill the chart;5. The soundings should spread in such a way that they form a net of rhomboidal shape.


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1.2 The Difficulties

The soundings selected by the first three rules are usually scattered on the chart irregularly. When in the manualgeneralization, Cartographers have to repeat the selection procedure for several times to attain satisfactoryresult that best represents the underwater relief while soundings scatter in the required pattern. Not only theknowledge and steps of thinking for this job is highly complex, difficult to explain, thus hard to computerize inordinary ways, the processing of both depth values of soundings and scattering pattern of them interactively atsame time also cause great problems. A possible way to deal with this situation is to examine the inner motionof thinking of human beings to solve similar problems, trying to take into consideration as many factors aspossible, and then learn from the natural problem-solving method of manual work.

2 The design of Artificial Neural Network for Sounding Selection

2.1 Basic Idea

Hierarchical Information Structure (HIS)[3] is a pattern to solve theproblems with partly-known knowledge of it. The idea of problem-solving by HIS can be simply explained as the following. (1) if theknowledge is not enough to solve the whole problem, try to dividethe problem into different parts; (2) search for the answer to eachpart with what we have known now, the answer(s) will add somenew knowledge; (3) try to attack more parts of the problem by thenew extent of knowledge; (4) loop till all finished. Not very precise,but it does work.

From the main idea of HIS and theory of neural network, wedesign a method of sounding selection. Two significant pointsdistinguish our method from the usual way of sounding selection.First, we divide the whole scattering area of soundings into smallsub-area (sounding patch), the selection of soundings is gradu-ally finished, from the selection of sounding patches to the selec-tion of individual soundings. Second, in each selected soundingpatch a sounding is left on the chart and the others are omitted.So the selection or deletion will be determined not only upon thesounding itself, but also upon the surrounding terrain features.

2.2 Structure and Strategy

Many models and structures of neural network have been proposed,but none suits the generalization problem very well. Based upon theprocessing ideas above, we designed a neural network for our spe-cial purpose. The network is basically a combination of two back-propagation networks (fig. 1). The first part deals with the process-ing of sounding patches, and the upper one do the final selectionworks. Data are put forward layer by layer (serial connection), whilesome special info (such like “dangerous sounding”) can yet be passeddirectly to the upper layer (parallel connection).

Fig.1 Structure of Neural Network forSounding Selection


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2.3 Factors and Learning

The factors are those items of info about the characteristics of the soundings. The network makes selectiondecisions by working on the factors. More factors employed, the decision may get more reasonable, but on theother hand the network may become less stable. In the experiment we selected 16 factors for the process ofsoundings in each patch, and 17 factors for the evaluating of sounding patches. Some of them include:

Type (italic, upright, dangerous, etc.);

Value of depth;

Minimum distance to the fore-selected soundings;

Minimum distance to shore and inter-tidal area;

Minimum distance to obstacles;

Whether surrounded isolatedly by depth contours;

Depth difference to the surrounding depth contour;

General info of chart;

General info of sea area;

etc.

Factor set for sounding patch, which is somehow “of area type”, is slightly different to that for individualsounding. For example, those info about the area feature “in patch area”, such like the mini-terrain type (peak,range, valley, basin, or slope, etc.), sounding density, greatest depth difference, etc., are concerned.

Weight training of the network is by backpropagation algorithm. It adjust weights by[1]

W W Wk k k( ) ( ) ( )( )= + ⋅− −1 1α ∆where

∆(W) = ∇ E(W) = −=∑1

1nt W d t y t W

p t

n p

ϕ ( , )( ( ) ( , ))

which can guarantee a local optimal solution.

Result and Study

The experiment is based upon the discussions above. As the preparing work, three sheets of navigation chart ischosen to set supervised learning samples, which summed up to approximately 500 training areas. Also, some100 designed training areas are used to complete the types of patch feature.

Figure 2 shows a sea area in South China Sea, generalized by the protocol network. Fig.(a) is the source and (b)is the result. Main requirements of sounding selection have been satisfied in the result figure, yet it is hard tosay the system is powerful enough. Further research is been planning (including the combination with expertsystem, knowledge-based system and fuzzy mathematics, etc.) and we welcome cooperation and suggestions.


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Fig.2 Result of experiment

Reference

1. Fu, L.M. (1994), Neural Networks in Computer Intelligence. McGraw-Hill, Inc., New York.

2. Tian, Z., Wang, J.Y., Liang, K.L. (1997), Design of Neural Network for Automated Selection of Soundings inNautical Chart Making, Proceeding of 18th ICC, Stockholm.

3. Tian, Z. (1997), Research of the Automatic Cartographic Generalization Based on Artificial Neural Network, Ph.D.thesis, Zhengzhou Institute of Surveying and Mapping, Zhengzhou, China.

4. Ziborov, V.V., etc.(1989), Generalization of Depth in the Modeling of Bottom Relief, Mapping Science and RemoteSensing, New York


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Session / Séance 02-C

Performance Measurement of Combined Versus SeparateRadar and Electronic Chart Displays

Don C. DonderiHuman Factors North Incand McGill [email protected]

Sharon McFadden Defence and Civil Instituteof Environmental [email protected]

Abstract

There was no published evidence to say whether combining the information available in marine radar with theinformation available in electronic charts on the same display screen would help or hinder the use of thisinformation in marine navigation. We carried out a laboratory experiment in which information had to beobtained from either a radar plot or from its associated electronic chart, or had to be combined from both theplot and the chart in order to correctly respond to true-false statements like: “There is a ship return to thenorth of Ownship” (radar question), or “Radar shows a ship return approaching St. Mary’s Island” (radarand chart question), or “There is a large building at the end of Smith’s pier” (chart question). Eighteeninexperienced (college undergraduates, average age 21) and nine experienced (deck officers, average age 35)observers were given written instructions and practice in using marine radar and electronic chart displays.They then answered true-false questions about the radar and chart displays . Half of the questions were presentedwith the radar and the chart displays on separate adjacent monitors, and half were presented with the radarimage overlaid over the electronic chart information on the same display. Observers responded as rapidly asthey could consistent with being confident that their answers were correct. The pattern of results was the samefor both officers and students. They were equally accurate (71 percent correct overall), and equally accurateon the overlay and the separate displays. Officers were slower to answer than students, but officers and studentsalike were faster on the overlay displays than on the separate displays. Questions requiring radar informationalone were answered fastest; questions requiring chart information were answered next fastest, and questionsrequiring the integration of chart and radar information were answered slowest, and this was true whether theinformation was displayed on separate or overlaid displays. A measure of efficiency (percent correct/viewingtime) was at a maximum for chart-radar pairs that had an intermediate level of subjectively judged dissimilaritybetween the radar and the chart displays. We conclude that information from overlay displays is evaluated justas accurately as, and faster than, information from separate radar and chart displays regardless of what kindof information: chart, radar or a combination of both, is needed to evaluate the statements about the displays.


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Introduction

Marine navigation and piloting procedures and display standards are in flux. From the 1950s to the present,navigation and piloting has been carried out with paper charts, land-based electronic positioning systems likeLoran, and celestial fixes, aided when possible by radar ranges and bearings. Courses were planned and plottedon paper charts. The charts were corrected by hand as changes to navigation aids, soundings or topographywere collated and distributed to users by the national hydrographic services (Maloney, 1978).

An automated display of ships’ position information was added to paper charts when Loran-driven plottingpens were set to mark a ships’ track on paper charts. A similar position display was based on an inertialnavigation system that mechanically projected spot of light, locating the ship on a paper chart (Millar & Hansford,1983).

Radar technology also advanced to the point where marine radar systems can identify moving targets, extrapo-late their courses, and predict and display a calculated closest point of approach. However, research with theseadvanced radar plotting aids (ARPA) shows that large individual differences in navigation styles, encompass-ing a wide range of risk-taking tolerance, are still found among navigating officers even when using ARPA(Habberly et al, 1984), and “radar-assisted collisions” continued to occur.

Until recently no single positioning system was accurate enough to provide the necessary confidence to locatea ships’ position on a large-scale chart. Now, a combination of computer-assisted dead reckoning, Loran, localmicrowave positioning systems, and differential GPS, (a world-wide satellite network supplemented by groundstations), make it possible to produce a single navigtion display image that locates the ship on an electronicchart with an error measured in meters, and superimposes properly oriented and scaled radar returns over theship and chart image (Rolfe, 1996, Baziw, 1996). The integrated display image also contains a character-basedsummary of relevant navigation information including speed and heading, progress along a predeterminedtrack, deviation from the track, and the status of the positioning information used to locate the ship on the trackand display. These combined displays are called electronic chart display and information systems (ECDIS).They are currently installed on many Canadian lake carriers and are increasingly being installed on ferries andocean-going ships.

The task of the marine navigator or pilot can be either ameliorated or complicated by the layout of the com-mand and control equipment on the bridge (Schuffel, 1985). Driven by human factors/ergonomics researchand analysis, ships’ bridge designs have evolved over the past twenty years to allow the safe and efficientoperation of large ships by minimum navigating crews, consisting at times of only one officer (Herman, 1977;Istace, 1977; Hall & Anderson, 1980).

Most of the bridge design studies preceded the development of ECDIS displays. Many design and operationalquestions remain to be answered about the deployment and use of ECDIS displays, including: Where shouldthe display be put? What information should appear on it? In what format should the information appear? Howshould the informatin display be controlled? How should ECDIS be integrated with other navigation aids?How should navigators be trained to use ECDIS displays? In the absence of any empirical or analyticalstudies, these questions are answered by applying local expertise or local opinion whenever a decision has tobe made. The last word in bridge layout and equipment installation is almost always that of the owner’s repre-sentative, usually a senior captain, who supervises the fitting-out at the dockyard. But the optimum locationfor, the optimum format for, the optimum use of, the optimum training on, and the optimum integration ofECDIS displays into the piloting and navigation process have been neither systematically analyzed nor empiri-cally investigated, at least in the open literature.

The study reported here begins to investigate one capability the marine navigator gains from ECDIS: theability to superimpose a properly oriented and scaled version of the current radar return onto the electronicchart, with the ship’s position indicated on the chart corresponding to the origin of the radar returns. The radar


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is overlaid in a “transparent” mode so that radar returns and the chart information beneath the returns aresimulataneously visible.

The combination of a reliable ECDIS display with reliable superimposed radar might be thought to give thenavigator all the information needed. The chart display indicates the location of fixed hazards to navigation,the soundings, the recommended traffic lanes, etc, while the radar displays the transient hazards to navigationincluding other ships, icebergs, floating debris, etc, as well as the location and identity of radar-respondinglights, buoys and ranges.

But radar returns are ambiguous and may be incomplete, electronic chart information may be out-of date, thepositioning sensors may be damaged, and local aids to navigation like radar beacons, buoys, etc may have justbeen damaged or destroyed. Experienced navigating officers know that chart information and radar returns areno substitute for continuous human visual verification, both at sea and in pilotage waters.

So at the onset, ECDIS displays, even more than ARPA radar displays, offer the navigating officer the tempta-tion of sticking his or her head into the display hood and keeping it there, to the detriment of common sense andsound navigation practice. This hazard, like “radar-assisted collisions” can be avoided through proper training.The fact that a good source of information may be abused does not mean that it must be abused, and thesuperimposition of radar and ECDIS displays may very well have real advantages that outweigh these potentialhazards.

The focus of our studies was on the use of radar information and chart information either superimposed on thesame display screen, or separately on two adjacent screens. Our studies were carried out in a laboratory asopposed to a marine or marine simulator environment. Therefore there was no potential distraction from, orconflict with, other sources of information about either the ship or the navigating environment.

The reason we were interested in radar-chart superimposition is that in many circumstances display complex-ity is known to have a deleterious effect on both the accuracy and speed with which information can be ex-tracted from visual displays. Superimposing radar information on electronic chart information increases thecomplexity of the resulting display, by comparison to the two simpler original displays (radar alone and chartalone). On the other hand, it takes less head movement and fewer eye fixations to visually scan observe thesmaller area of one display screen than it does to scan the larger, disjunct areas of two screens; therefore theremay be a counterevailing advantage in displaying both radar and chart information on the same screen. Therelative advantage of one versus two screens may be also be influenced by the complexity of the superimposeddisplays, so the answer: one screen or two? may very well depend on the particular chart and radar returnsdisplayed.

The goal of this study was to determine under laboratory conditions, what differences were observable inextracting useful navigating information from one superimposed chart and radar display, as opposed to twoseparate, side-by-side displays, one of which displays radar information and the other, the matching chartinformation. We presented statements about the displays which the participants had to evaluate as either “true”or “false”, as rapidly and accurately as they could. The participant had to read the statement, decide whatinformation was needed to evaluate it, and then look for that information on the display or displays. We carriedout the study using university undergraduates who were given written information about marine radar andelectronic chart imagery, and who were then allowed to practice, before beginning the experimental tasks. Wealso recruited participants among experienced marine navigators including Canadian Navy officers and com-mercial captains and deck officers.


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Experimental Method

Displays

Fifty-two electronic chart images were obtained from a Canadian marine simulator installation. The chartscovered coastal areas of Newfoundland and Norway, and Halifax, N.S. and New York harbors. The colorrendering of these charts was corrected to IMO standards by the research team. The charts ranged from thesubjectively very simple to the subjectively very complex. (These subjective descriptions were quantified inanother study, not reported here).

Each chart image had an associated radar image. The radar images were generated by a simulator controlcomputer from a position corresponding to the “ownship” symbol on the chart. An overlay image was gener-ated for each chart-radar pair. The separate chart and radar images were carefully superimposed, and thenscaled and rotated so that radar landmarks corresponded to the appropriate chart symbols, and the radar coast-line matched as closely as possible the chart coastline. Then each superimposed pair was saved for use as achart-radar overlay display.

Presentation

The task required that the participant observe either one or two display screens. The physical arrangementconsisted of two identical 17 in SVGA display monitors (AcerVue 76e) placed side-by-side, and a single 101-key computer keyboard placed beneath the right-hand display. The keyboards and displays were placed on adesk at 72cm from the floor, and the particpant sat in front of the displays on a secretarial chair. The experi-ment was carried out under ambient illumination of 300 lux, measured at the keyboard, provided by overheadfluorescent fixtures which did not produce glare on either display screen.

Experimental Task

Statements Six different statements were written for each chart-radar display pair. Two of the statements couldbe confirmed or disconfirmed by information that could be obtained exclusively from the radar display withoutreference to the chart display, two depended on information that could be obtained exclusively from the chartdislay without reference to the radar display, and two required that information be combined from the chart andradar displays.

Displays The entire display presentation sequence was controlled by computer but was paced by the partici-pant. The sequence began with a message “Press any key to see the next question” in white characters at the topof one of the two blank (black) display screens. The screen displaying the messages was consistent for eachparticipant but randomly varied between participants. When the participant pressed a key, the statement chosenfor that trial appeared and a question duration timer started. The participant read the statement and when he orshe was ready, pressed any key to present the display and start a display duration timer. The “separate” displayson both screens were always presented with the radar on the left screen and the chart on the right screen, but theoverlay displays were presented on either the left screen or the right screen, consistently for each participantbut randomly between participants. When the participant had decided whether the statement was true or false,he or she pressed the “T” [rue] or “F” [alse] keys on the keyboard to record the response, stop the timers anderase the statement and the displays. These keys were marked with colored stickers so they were quite con-spicuous. Then the “Press any key to see the next question” message appeared at the top of the blank messagescreen, in preparation for the next trial.

Instructions All participants received written instructions at the beginning of the experiment. For the universityundergraduates, the instructions briefly explained the nature of marine radar, the nature of electronic chart


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display systems, and the purpose of the study (see Appendix 1). A glossary of chart symbols was continuouslyavailable during the experiment. The navigating officers received shorter instructions that simply explained thepurpose of the experiment. However, each officer was thoroughly debriefed after participating to elicit com-ments about both the experimental study and EDCDIS displays in general.

Randomization The fifty-two image sets were randomly assigned for each participant to three separate tasks:true-false practice, true-false test and map-matching (Map-matching results are not discussed in this paper).Ten images were assigned to the true-false practice sessions, thirty-two to the true-false task, and ten to themap-matching task.

On the true-false practice and test tasks, there were six display presentations of each image set: one presenta-tion for each of the six statements written for that set. Thus there were a total of sixty (10 x 6) presentations inthe true-false practice task and 192 (32 x 6) presentations in the true-false test. The presentations were randomizedwithin participants with respect to which image sets appeared in which part of the study (practice, true-falsetest or map-matching). They were also randomized with respect to which presentations appeared in either theoverlay or separate display conditions. Finally, the order of presentation for the displays accompanying the sixquestions for each image set was also randomized. In other words, the true-false experiment was executedusing a within-subject design in which everything was randomized across the classication variables of displaytype (separate or overlay) and question type (radar, chart, or radar+chart).

Participants

Eighteen McGill University undergraduates participated. Five were men. The average age was 22 and therange was from 20 to 27. Nine experienced navigators participated, all of whom were men. They ranged in agefrom 25 to 55. Three of them were Canadian Navy officers, ranging in rank from lieutenant-commander tolieutenant. Two were on active duty and one was a reservist. Six were commercial masters or deck officers,ranging in seniority from the captain of a lake carrier to a former second officer now enrolled in a managementprogram at McGill. Seven of the navigators were currently seagoing.

Data Recording and Analysis

The data from a practice task that consisted of the first ten samples (sixty trials) of the true-false task, were notanalyzed. Data collected from the remaining true-false tasks included the time required to read each statement,the display time for each display, and the answer returned (True or False). This made it possible to assignanother value (Right or Wrong) to the answer associated with each question presented with each display.

The classification variables were the type of display (separate or overlaid) and the type of question (radar,chart, or radar+chart). Variables associated with each display included the subjectively obtained complexityratings for the radar, chart and overlay presentations, and the subjectively judged dissimilarity of each radar-chart pair.

The general linear model of analysis of variance was used to analyze the output data from the true-false task,because as a result of the randomization of display condition (separate versus overlay), the variations in thedistribution of answers (True and False) across displays, and differences in the number of correct responses(Right or Wrong), the number of data entries per analytical cell varied across participants. In all analyses,observers were treated as a random variable.


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Results

The effects reported here are those that were consistent between officers and students. Some analysis-of-variance interactions were “significant” without being “important’, and those are left for future discussion andelaboration.

Correct Responses

Officers and students were equally accurate at the task: officers with a proportion of 0.706 correct responses,and students with a proportion of 0.707. These proportions are not significantly different. Both officers andstudents were more accurate with statements for which the correct answer was “False” (Table 1).

Table 1. Proportion Correct: Officers and Students on “True” and “False” Statements

Participant Group “True” correct answers “False” correct answersOfficers 0.6395 0.7728Students 0.6568 0.7132

There were consistent difference for both officers and students in the proportion of correct responses across thekind of information (radar, chart, or radar + chart) required to evaluate a statement, and the type of statement(correct “True” or correct “False”) (Table 2). Notice that the officers were consistently more accurate than thestudents on the “False” statements, while the students were more accurate on the “True” statements.

Table 2. Proportion Correct: Officers and Students on “True” or “False” Chart, Radar or Chart+Radar Statements

Information Radar Chart Radar+ChartType True False True False True False

Officers 0.594 0.781 0.649 0.803 0.676 0.734Students 0.671 0.764 0.663 0.754 0.702 0.687

Display Duration

Officers took longer on the average (15.43 sec) to respond to the statements than did students (12.34 sec). Thisdifference was highly significant. Officers and students took longer to respond when they were wrong (15.87sec) than when they were right (13.10 sec); again highly significant. And both officers and students took theleast time to respond to radar questions, more time to respond to chart questions, and the most time to respondto radar+chart questions (Table 3).

Table 3. Display Duration: Officers and Students on Three Types of Question

Participants Radar questions Chart questions Radar+Chart questionsOfficers 13.88 16.11 16.32Students 10.89 12.54 13.60


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Efficiency

Our measure of efficiency for every condition was the proportion of correct responses divided by the imagedisplay duration; or, in other words, accuracy achieved divided by the time taken to achieve it. On this stand-ard, the students, whose responses were much faster, were more efficient (0.067) than the officers (0.057), ahighly significant differenct. This measure aksi differed significantly for both display screen (Overlay versusSeparate) and Statement Type (Radar, Chart, or Radar+Chart), for both officers and students, as shown inTables 4 and 5

Table 4. Efficiency Measures for Separate and Overlay Screens

Participants Separate Screens Overlay ScreenOfficers .070 .063Students .061 .053

Table 5. Efficiency Measures for Radar, Chart and Radar+Chart Questions

Participants Radar questions Chart questions Radar+Chart questionsOfficers .063 .059 .050Students .075 .067 .058

Conclusions

There was no performance penalty attached to overlaying radar displays on electronic chart displays. Regard-less of whether the true-false statement that was evaluated concerned the radar display alone, the chart alone,or required a synthesis of information from those two sources to evaluate correctly, the evaluation was carriedout as accurately on the overlay as on the separate display, and it was carried out faster on the overlay displayby both officers and students. Because the accuracy of the responses to separate and overlay displays was thesame, the efficiency of the overlay displays was also higher.

As a first approximation, then, we can say — based on a laboratory study under static display conditions —that superimposing a marine radar display over an electronic chart display does not make the information ineither display harder to evaluate. There are practical limitations to our conclusions, some of them pointed outin our interesting conversations with the marine navigators who participated. All of these chart and radarimages were simulating long-range, small scale charts and radar displays. There was some clutter caused bythe Ownship return, but very little of the sea clutter that the mariners told us would likely interfere on the radardisplay with a short-range setting, and so make the chart information “under” the transparent radar displayharder to read. A static display is by nature ambiguous with respect to radar information, because much islearned by observing the changes in the radar display over time. Dynamic displays, and short-range use, mightgive different answers to the question we studied here. In the meantime, it is clear that one property of ECDISdisplays — the ability to superimpose radar and electronic chart imagery — may be a real advantage to themarine navigator.


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References

Baziw, E. (1996). Field Trials of ECPINS Vessel Positioning Algorithm. IEEE Position, Location and Navigation Sym-posium, Altanta, GA, 121-129.

Hall, J. W. & Anderson, M. D. (1980).The U.S. Coast Guard Multi-Mission Cutter: Command, Display and Control(COMDAC). Naval Engineer’s Journal, 92(35), 59-69.

Habberley, J. S., Shaddick, C. A. & Taylor, D. H. (1984). A behavioral study of the collision avoidance task in bridgewatchkeeping. Report to the Marine Directorate, Department of Transport, U.K.

Herrman, R. (1977). Two studies for optimizing operating bridges and their application in inland and sea-navigation.Human Factors in the Design and Operation of Ships: Proceedings of the First International Conference onHuman Factors in the Design and Operation of Ships, Gothenberg, Sweden,, 58-68,

Istace, H. (1977). An experimental evaluation of a “one-man control” bridge .layout. Human Factors in the Design andOperation of Ships: Proceedings of the First International Conference on Human Factors in the Design andOperation of Ships, Gothenberg, Sweden 167-173.

Maloney, E. S. (1978) Duttons’s Navigation and Piloting, 13th edition. Annapolis, Md., Naval Institute Press.

Millar, I. C. & Hansford, R. F. (1983). The ‘Manav’ integrated navigation system. Journal of Navigation, 36(1), 81-92.

Rolfe, G. A. (1996). Radar image overlay on an ECDIS system - an overview. IEEE Plans, Position Location andNavigation Symposium, Piscatawnay, NJ, 130-136

Schuffel, H. (1985). Determining effects of bridge design on ship control. Society of Naval Architects and MarineEngineers, STAR Symposium, Norfolk, Va, 275-283.


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Session / Séance 02-A

The Challenges of Production of ENC Cells and Paper Charts fromone Common Database

Tiina TuurnalaFinnish Maritime AdministrationDepartment of Hydrography and Waterways,Porkkalankatu 5, 00181 Helsinki, FinlandPhone: +358 204 48 4426Fax: +358 204 48 4620e-mail: [email protected]

Ismo LaitakariFinnish Maritime AdministrationDepartment of Hydrography and Waterways,Porkkalankatu 5, 00181 Helsinki, FinlandPhone: +358 204 48 4407Fax: +358 204 48 4620e-mail: [email protected]

Abstract

Previously, the main purpose of nautical chart databases was the production of paper charts. Advances innavigation technology, e.g. satellite positioning systems, have set new demands on data accuracy, reliabilityand the format of data. The Hydrographic Offices are required to produce more and more accurate charts andespecially electronic navigational chart (ENC) data. This rapidly increased need for electronic chart data hasled many offices to a situation where there are two separate production lines for two products, ENC cells andpaper charts. However, it is vital for the safety of navigation that the content of data is exactly the same in bothproducts and the products are not in conflict with one another. It is also a waste of time to do the same updatestwice in two different databases. Research and development in many Hydrographic Offices is now concentratedon the problem how to combine electronic and paper chart production?

The Finnish Maritime Administration is developing a new data management and chart production system. Thedevelopment project is called the HIS (Hydrographic Information System) Project. The project is divided intotwo phases, the first phase containing development of a data management system and an ENC production lineand the second phase development of a new paper chart production line which uses the new data managementsystem. At the time of writing, the data management system, project phase 1, is about to be ready for testing. Atthe Finnish Maritime Administration the question of the day is how to implement the new chart production line,which confirms that different products (ENC and paper chart) are not in conflict with one another.

This paper starts with a general description of the present state of production of nautical charts and ENC data.The paper then outlines the problems and challenges which must be solved before it is possible to producethese different kinds of products, ENC cells and paper charts, from the same database. This is done by comparingthe characteristics of the products and by introducing some solutions how to handle these differences.


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1. Introduction

1.1 Background

Navigation practices have changed dramatically over the last 10 years due to the modern global positioningtechnology. Navigation had traditionally been based on visual observations and radar measurements, whichgive an indication of current position on paper chart. This method is called ’relative navigation’. Nowadaysnavigation is to a great deal based on so called absolute methods. These satellite driven services, such as GPSand Differential GPS and Russian GLONASS are already widely available. A European option, GNSS, will beoperational in due course.

Specific requirements of nautical chart production compared to topographic map production:

• Accuracy of the data affects directly to the safety of navigation• The requirements for the correctness of the data are very high• Different nautical products must be consistent• There must be arranged a rapid updating service

New technology requirements for the nautical charts:

• the positional accuracy of the chart data must meet the increased accuracy of the positioning systems (e.g.DGPS 1 – 5 m).

• in order to fully benefit from the dynamics of the modern positioning methods, there must be availabledigital chart products parallel to the traditional paper charts. These would allow real time tracking of ship’sown position on chart display system.

• digital data contains valuable information of chart features and the navigator does not necessarily have tosearch for that information from printed nautical publications.

• there must be arranged on-line updating services for the digital products

The focus has been on pure technical development and therefore it has become evident that the effects of the newinfrastructure to the content, production processes, distribution services and use of nautical chart products has re-mained vague.

1.2 The urgency of theENC production

Shipping companies have, for sometime now, requested electronic chartsystems, which would meet the re-quirements of both the navigator andInternational Maritime Organisation’sSOLAS convention as well as properchart data for these. Relevant inter-national standards for ECDIS (Elec-tronic Chart Display and InformationSystem) and ENC (Electronic Navi-gational Chart) were issued fairly late1995 and 1996 by the respective bod-ies and this has caused difficulties infulfilling the commitments towardsthe end users.

Figure 1 Information sources of the Electronic Chart Display andInformation System


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The division of work has however been quite clear: The end user requires services, regulatory bodies announcestandards, private system manufacturers develop ECDIS and other charts systems and national hydrographicoffices put efforts into ENC production. Most of the hydrographic offices have chosen the fastest solution tothe ENC production challenges. They vectorise current paper charts as such into ENC format. Only a littleextra information is added apart from the information content of the paper chart.

In Finland we are in a situation, where approximately 50% of the national sea area is already covered by vectordata (internal Fingis format) whereas the rest of the water areas are covered by manually maintained charts.Almost all of the Finnish navigational aids (beacons etc.) are however in a common Oracle database and theinformation is available in digital form for many purposes, including chart production. We are currently takinginto production use a new system called HIS (Hydrographic Information System), which:

• uses vectorised chart data (Fingis) and navaids information (Oracle) as main source data

• allows editing, quality assurance and storing to a seamless HIS database

• enables updating, multiple scales and history management as well as other traditional database managementfunctions

• allows to produce ENC data and its feature based updates according to pre-defined product definitions

The benefits of this arrangement include the ability to exploit in the new ENC products the hard work alreadydone in processing Fingis data for the current printed chart production purposes. The key weaknesses are two-fold: The first deficiency is related to the big differences of the Fingis and ENC data structures, which cause alot of interactive work when converting Fingis files into the HIS system. The other is the need for duplicatedmaintenance and updating of chart data for both the printed chart production (making all accrued changes intoFingis files before printing) and ENC production (continuous updating of the HIS database).

1.3 Finnish Maritime Administration aims to unify ENC andprinted chart production processes

There are many good reasons to unify the production of ENC and printed charts:

• common production line increases the level of the consistency between the products. That has positiveeffects to the quality, which increases the safety of navigation

• a single, combined process flow instead of a duplicated one will make data management more efficient andreduce the costs

• it will be easier to develop the content of the products when the production line is well integrated. This willhave positive effect to the provision of the services to the mariners

We have started at the Finnish Maritime Administration a project for replacing the well served FINGIS (Finn-ish Geographic Information system) system with a new printed chart production line, which would not onlybring improvements to the production of printed charts but also facilitate closer integration with the HIS sys-tem and the ENC production.

During the system specification feasibility study we have met several problems which have to be solved beforesystem implementation. This paper outlines three remarkable ‘challenges’ which must be solved before it ispossible to produce ENC cells and paper charts from the same database.

These ‘challenges’ are as follows:

1. Cartographic presentation

2. Multiscale data management

3. The relationship between updating of printed charts and ENC cells


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2. Cartographic Presentation

2.1 Differences in printed charts and electronic navigational charts

Printed charts present all important information as chart objects with appropriate symbology and descriptivecartographic information texts and symbols. The volume of information is limited due to the size of the chart aswell as the readability aspects of it. One of the most important preparation work of the data to be published onthe printed chart is cartographic generalisation and cartographic editing of the data. This includes e.g. displace-ment, aggregation, selection, rotation and text width, font and placement [Jatkola, M. and T. Tuurnala, 1998].

ENC data is presented on the CRT display of the ECDIS. The symbology of the chart objects is determined bythe object class and its attribute values as well as very dedicated conditional symbology rules, which take intoconsideration the current navigational situation and the nature of the surrounding data. It is easy to add andremove information on the ECDIS display, the user can select which object classes he wants to be visualised onthe display (except ‘display base’ object classes) [IMO, 1996]. A large part of the attribute information doesnot affect to the symbology, and the mariner can have an access to the information by a simple spatial queryfunction. Some of the features do however have suchimportant attribute information that is displayed onthe screen as text without any separate query, if themariners choose that display option. ENC data alsouses so called meta object classes in order to providethe mariner with information about e.g. the quality ofthe chart or the direction of boyage system appliedlocally. Should tidal information or traffic restrictionsexist, these can be presented as raster images or textfiles, which are stored as ‘annexes’ to the ENC fileand opened by attribute query to the appropriate ENCobjects on the ECDIS display.

2.2 Challenges

The level of the presentation detail in ENC informa-tion is not limited by the size of the display and itsreadability aspects in a same manner as in paper chartssince the user can select which information is pre-sented at each moment. The real core of the problemis the question of how to unify the production proc-esses and data management of the two navigationalchart products i.e. ENC and printed charts.

2.3 One possible solution

Our principal hypothesis is that the major part of thesymbology of printed charts can be directly deter-mined from the information stored into ENC objectclasses and attribute values. Only a minor part, i.e.pure cartographic information, will need additionalobject classes or attribute fields apart from the stand-ardised ENC data content.


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An example of a need for additional attributation in order to provide good symbolisation in printed charts:Figures 2 and 3 present lateral marks in ECDIS symbology, where zooming of chart display helps in keepingthe view clear. Figure 4 presents the method in printed charts, i.e. rotating the spar buoys in order to allow allthe information to fit into available space. This rotation of buoys could be handled with one additional attributecompared to pure ENC object model. Another good example is the displacement of depth figure. In ENC thedepth figure has to be exactly in the correct position, but sometimes this is not possible on paper chart becauseof limited space. This can also be implemented by additional attributes (displacement, dx, dy).

3 Multiscale Data Management

3.1 Research Problem

Multiscale data management is one of today’s key research topics at the field of cartography science. Multiplerepresentation and generalisation has been regarded as one of the most difficult tasks of the cartographer. Inmultiple representation databases the same objects/features are presented in separate layers that provide vari-ous spatial resolutions and degrees of details. There are several alternative solutions to handle the problem ofmultiscale data management but however many problems at this area are still unsolved. Here the problem ofmultiscale data management is approached from the point of view of nautical charting. The multiscale datamanagement as part of the problem of integrating the production and data management of two different kind ofproducts, ENC and paper charts, makes the problem of multiscale management even more challenging.

Traditionally, digital nautical chart data has been prepared to be published at a certain unambiguously specifiedscale on printed chart. The purpose of databases has been the production of paper charts. This way the carto-graphic generalisation and visualisation of the data can be modified to serve the needs of one certain scalepaper chart. However, this traditional method is not sufficient anymore, because of a completely new kind ofproduct, electronic navigational chart. Types of paper charts published by the Finnish Maritime Administrationare presented in the Table 2.

ENC has set new demands on presentation and visualisation of the data. The data is planned to be visualised onthe screen in different scales defined by the user (zoom-in, zoom-out). ENC data is also produced in scalerelated navigational purposes. These are defined by the S-57 standard, see Table 1.

Table 1. Definitions of navigational purposes of ENC [IHO, 1996; TSMADWG, 1998]

Navigational purpose Definition

Overview Oceanic crossing and route planning for large and/or longdistance crossing – Worldwide coverage.

General Commonly used as coast is approached from the open ocean orfor sailing along the coast, frequently outer sight of the coast,between distant major ports.

Coastal Navigation along the coastline, with well offshore courses,eventually intricate and frequently in sight of the coast.

Approach Near shore navigation to gain access to major ports throughchannels or marked areas leading to a port, and navigationthrough intricate or congested coastal waters.

Harbour Navigation in harbours or smaller waterways and foranchorage.

Berthing Sufficient data to allow a vessel to berth.


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The standard does not define the resolution (except the point density of linear features) or the degree of gener-alisation for each navigational purpose. The scale of “source data”, from which the certain navigational pur-pose ENC data is produced, is decided by the Hydrographic Office. In addition to navigational purposes, thepresentation of ENC data can be managed by the scale attribute (SCAMIN), which defines the smallest scalewhere the object is visualised.

Table 2. Scales of paper charts in the FMA at the moment. [FMA, 1997]

Type of chart Scale Definition

General chart 1:100 000 – 1:500 000 Intended for high sea navigation andvoyage planning.

Coastal chart 1:50 000 Intended for navigation in thearchipelago and on the coast.

Special chart 1:5 000 – 1:25 000 Intended to facilitate harbour traffic.

It has been noticed that the generalisation level of a paper chart at a certain scale is not sufficient to be visual-ised on the screen. E.g. aids to navigation, rocks and buildings cause problems (see figures 5 and 6).

3.2 Possible Solution to be studied

Our primary aim is to produce both ENC cells and paper chartsfrom one common database. This means that the database have tobe implemented so that production of two different kinds of prod-ucts in different scales is possible. Figure 7 presents a multiscalemodel where production of ENC and printed chart has been takeninto consideration. The basic idea is that the data stored in thedatabase scale layer is generalised for certain scale printed chart.To improve the readability of ENC the attribute ‘minimum scale’has been used (SCAMIN). This means that the object is visiblewhen using the attribute value or larger scale on a certain naviga-tion purpose.

The compilation scale of each navigational purpose (e.g. Coastal:1:50 001) has been determined by experimental research. The ba-sis of our testing was to use as detailed data as possible. In otherwords each navigation purpose data is used on as small a scale as isreadable. This smallest readable scale defines the compilation scaleof the next navigation purpose. E.g. the data on navigation purposeApproach is still readable in scale 1:50 000, but not in smaller scale.This defines the compilation scale of navigation purpose Coastal(1:50 001). The use of database scale layers for each navigationalpurpose is decided in order to correspond the definitions of naviga-tional purposes (see Table 1). The test data was Finnish MaritimeAdministration’s unofficial ENC data.

Figure 5. An example of ENC data onthe screen in scale 1:50 000.

Figure 6. A copy of 1:50 000 scale paperchart from the same area.


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Figure 7. Multiscale management model for ENC and paper chart production.

4 Updating Services

4.1 Distribution service for electronic navigational charts

The co-operative body of the European hydrographic offices, the Northern Europe RENC (Regional Enc Co-ordinating Centre) has introduced a commercial ENC distribution and updating service for mariners. Thisservice covers official ENC products from most of the European hydrographic offices and they are sold undera common brand name PRIMAR (see figure 8).

4.2 The relationship between traditional updating of printed charts and modern ENC updat-ing messages

This PRIMAR service has been faced with the question of how the publication schedule of NtMs (Notices toMariners –booklet, which is mailed to mariners in order to give him instructions to make needed chart correc-tions) and the production schedule of ENC update messages would have to be synchronised. The fundamental


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question for the HydrographicOffices is what their legal li-ability is regarding the re-quirement to provide digitalENC update messages at thesame time as their paperequivalents (NtMs for printedcharts). This question is re-lated to the status of digitalchart products like ENC ver-sus a traditional printed chartproduct. Are these consideredas two sovereign products,which are also updated inde-pendently, or are they basi-cally the same nautical prod-uct in two different media, butwith a common status interms of updating frequencyand schedule toward the enduser? The opinions among the European hydrographic offices differ and the grounds for the deviations can betraced back to the national practices and circumstances. Some hydrographic offices produce their ENCs di-rectly from printed charts and use the same chart correction cycle for both products. Other offices on the otherhand compile their ENCs from many different digital sources and they end up with a navigational product,which differs from the corresponding paper charts in many respects. The updating cycle may also differ. Theuse of this wider source information may cause situations, where a need for an ENC updating message may benecessary even though the change would not affect to the paper chart in any way.

4.3 Discussion

Closer harmonisation of the ENC and printed chart data content and production processes would ease theproblem of two updating services. If all the incoming correction information was treated in only one processleading to one update to one common database, there would be less need for publishing any ENC updatemessages or NtM notices in a separate cycle. This approach, if applied, would cause a change to the currentupdating practices of the printed charts. Updating of the data for printed charts has traditionally followedprinting schedules, but now, if two production lines were unified, a real-time updating of the data would bemore feasible.

In Finland our aim is a well-synchronised updating service, since we believe that it would be advantageous forthe mariners. We do not however see it necessary to come to any specific international decisions on the legalliability aspects of the relationship of the two updating services. Each Hydrographic Office should apply themost suitable practice according to the national legislation and their chart production processes.

Figure 8. The concept for ENC distribution and updating service


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5. Conclusions

In this paper the ‘key challenges’ of production of ENC and paper chart from one common database waspresented. Cartographic presentation and multiscale management are the most challenging aspects to be con-sidered when unifying the production. Here the problems are approached by comparing the characteristics ofthe products and introducing some solutions, but however, more studies are needed. It is evident that there aremany other aspects, which have to be taken into consideration, especially concerning the implementation ofthe database (technical aspects) and the updating process of multiscale database. It also is obvious that theproduction process (workflow) and the updating services can not be the same as before. Our intention is tocontinue the research and development and publish more detailed experiences later.

References:

Finnish Maritime Administration (FMA), 1997. Finnish Nautical Charts, Hydrography and Waterways DepartmentHelsinki, 20 p.

International Maritime Organization (IMO), 1996. Performance Standards for Electronic Chart Display and Informa-tion System (ECDIS). Resolution A.817(19).

Jatkola, M. and T. Tuurnala, 1998. Multiscale Data Management as a Part of New Chart Production Process. Master’sThesis, Department of Surveying, Helsinki University of Technology, 106 p. (in Finnish)

Kilpeläinen, T, 1997. Multiple Representation and Generalization of Geo-Databases for Topographic Maps. DoctoralThesis, Finnish Geodetic Institute, Kirkkonummi 1997, 229 p.

International Hydrographic Organization (IHO), 1996. S-57 – IHO Transfer Standard for Digital Hydrographic Data,Edition 3.0

Transfer Standard Maintenance and Application Development Working Group (TSMADWG), 1998. Proposed Clarifi-cations to S-57 Appendix B1, Annex A – Use of the Object Catalogue for ENC. Proposals from SHOM – FranceClarifications, TSMADWG meeting, Monaco 19-23 October 1998.


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An expert system approach for the design and composition ofnautical charts

Lysandros TsoulosCartography Laboratory, Department of Rural and Surveying Engineering,National Technical University of Athens,9, H. Polytechneiou St., 15780 Zografos, Athens, Greece.Tel: (30+1)7722730, Fax: (30+1)7722734email: [email protected]

Konstantinos StefanakisCartography Laboratory, Department of Rural and Surveying Engineering,National Technical University of Athens,9, H. Polytechneiou St., 15780 Zografos, Athens, Greece.Tel: (30+1)7722639, Fax: (30+1)7722734email: [email protected]

Abstract

The current digital cartographic systems do not incorporate tools to support an ‘automated’ map/chart designand composition procedure. This is due to the fact that cartographic design is a complex and rather subjectiveprocess, mainly based on the cartographic knowledge, which can not be easily described algorithmically. Onthe other hand traditional cartographic knowledge is perishing and is being substituted by map/chartspecifications which do not always cover the diversity of cases appearing in map/chart design and composition.Thus the digital cartographic systems – although constitute valuable tools for the production of maps/charts –do not lead to efficient and economic solutions. The utilization of the expert systems technology to substitute -in a certain degree – the human factor and to ‘absorb’ the knowledge required for the design and compositionof maps and charts, is a very promising solution. This paper elaborates - at a conceptual level - a ‘hybrid’system utilizing the technologies of Geographic Information Systems and Expert Systems towards the productionof Nautical Charts.

Introduction

The idea of the utilization of expert systems technology in a cartographic design and production environment,is not a new one. A number of serious attempts have been made [Forrest, 1995; Freeman and Ahn, 1984;Tsoulos and Stefanakis, 1997] which were successful in solving particular cartographic problems like carto-graphic design of small scale maps, name placement, sounding selection etc. It is evident that a ‘holistic’approach to the problem is required, which will possibly address map design and composition process, as awhole. Such an approach, beyond the software components of geographic information system and expertsystem, requires the full set of specifications used for the design of the specific cartographic product, whichwill be used for the development of the knowledge base of the system. Nautical chart, is one of the cartographic


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products covered by detailed specifications agreed and adopted by the international hydrographic community.The above mentioned standardization level, along with the relatively simple design of the nautical chart,constitute an ideal paradigm for the development of an expert system leading to its production.

In the framework of this project, an expert system (Elements Environment) interfaced with a GeographicInformation System (Arc/Info) is being used. Elements Environment incorporates through its knowledge base,the design and composition methodology and handles the wide variety of entities appearing in nautical charts.Rules capture the knowledge necessary to solve particular domain problems (i.e. resolution of graphic con-flicts) and they represent among other things relations, heuristics and procedural knowledge. Rules are sym-metric so they can be processed in either a forward or backward direction. Elements Environment provideswith a number of representational structures.

There are objects and classes to describe the cartographic entities. There are properties which are character-istics of objects and classes and slots which store information about specific objects and classes. Meta-slotsdescribe how the slots behave. Properties and values can be inherited from a class or object to another class orobject. Certain meta-slots can be inherited from a class or object to another object. In conjunction with rules,the expert system supports methods and message passing. Methods can be triggered explicitly after receivinga message from a rule or other method, or they can be triggered automatically following a determination madeby the system. Methods can also inherited down the object hierarchy.

Elements Environment is an agenda-based system. The agenda is a dynamic mechanism. It is the engine of thesystem that provides the central transformation between the perception of events and the actions the systemwill take. It is modeled after the notion of attention. At any time, the complexity of the real world can bereduced to a limited set of parameters and possible decisions. In turn they will affect the world and perhaps thevery next events or actions that were planned. Agenda-based programming incorporates the notions of con-flict-resolution which is a decision between different possible inference paths and nonmonotonic reasoning.The agenda incorporates forward and backward mechanisms.

The Geographic Information System (GIS) manages the geographic entities and provides for the requiredgraphic tools and the interface with the user of the system The system utilizes the entities stored in the carto-graphic database which has been organized according to the International Hydrographic Organization TransferStandard for Digital Hydrographic Data [I.H.O., 1996].

There are various architectures that permit the integration of a rule-based system into GIS [Smith and Jiang,1991]:

· To enhance a GIS and the relevant database with rule-based system capabilities, such as knowledge acqui-sition and representation techniques.

· To employ ‘loose coupling’, in which an application is written using an ES shell.

· To employ ‘tight coupling’ to facilitate communication between the rule-based system and the GIS.

· To build a fully integrated system.

Although the ideal solution would be a fully integrated system, this is not realistic for the time being. Wetherefore focus on a ‘loosely coupled’ system not only because of the significance of this architecture in GIS,but due to the functionality of such a system which includes the following:

· The provision of the services of an Expert System

· The triggering of external actions in response to Expert System evaluation of rules

· The provision of state constraints, including referential and semantic integrity constraints.

When the efficiency of this environment is proved, this will justify the design and implementation of a fullyintegrated system.


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The chart production process

The production of a nautical chart with the utilization of the ‘system’ is implemented through the followingphases: Area Definition, Selection of Chart Information, Transformations, Identification of Portrayal Method,Graphic Conflict Resolution, Portrayal of Symbols and Texts, Generation of Supplementary Chart Information(e.g. tittle, tables, notes), Production. The degree of involvement of the expert system and of geographic infor-mation system, varies from phase to phase, due to the nature of the processes inherent to each phase.

We can generally distinguish the phases and the relevant actions of chart design and composition process tothose based on ‘knowledge’ and those based on ‘algorithms’. The first category includes the phases of Selec-tion, Identification of Portrayal Method and Graphic Conflict Resolution. These processes are being resolvedin the Expert System environment. In the following paragraphs the phases of Method of Portrayal Selection(Design) and Graphic Conflict Resolution (Composition) are elaborated.

Conceptual framework

The portrayal of cartographic entities on the chart is dictated by their degree of importance, their relationshipwith the surrounding entities and the size of the respective symbols. It is evident that the problem is a gener-alization problem.

A ‘holistic’ approach to this problem would entail the simultaneous participation of all entities to the generali-zation process at first place. This would lead to a very complex and uncontrollable process. If this approachwere substituted by a layered one, the layers and the entities assigned to them would be members of a hierarchi-cal structure implying that entities which are members of the higher levels dictate the portrayal of entitiesbelonging to the lower ones. The same logic can be applied for the entities belonging to the same layer.

The above mentioned approach must be embedded to a digital generalization model suitable for the integrationof expert systems technology. The Brassel and Weibel, model [Brassel and Weibel, 1988] consisting of struc-ture recognition, process recognition, process modeling and process execution – with minor modifications - isconsidered to be the most appropriate one, due to it’s inherent characteristics which serve efficiently the re-quired processes. The modifications refer to the operational steps (process execution) where the system pre-sented here, distinguishes the generalization at the layer level with the generalization at the object level.

Knowledge base architecture

The expert system applies two main representational paradigms: objects and rules. The system designer de-scribes the ‘world’ (the nautical chart with its entities) in terms of physical symbols (objects), generalizationsof physical objects (classes), parts of physical symbols (sub-objects) and attributes of physical objects (proper-ties). The knowledge in the domain is coded in the form of rules which constitute the ‘building’ components ofthe knowledge base. The application logic and the procedural information of the system, is described by rulesand operate on objects, classes and slots.

The knowledge base of the expert system for the design and composition of nautical charts, contains thefollowing categories of rules:

· Selection rules serve the selection from the database of those entities required for the chart production. Theselection rules generate the representations of chart entities to the object-orientated structure of the system

· Design rules give cartographic ‘substance’ to the entities of the representation


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· Composition rules make the appropriate changes to the portrayal of the chart entities in order to resolve theundesired events, according to the agreed chart specifications

· Procedural rules control of the overall process and guide the system through the various phases

The expert system enables the modularization of the knowledge base, by breaking it up into several knowledgebases. This feature is being utilized in this application, in order to provide efficiency and assist control duringthe development of the system. The selection, design, composition and procedural rules, are organized intoseparate knowledge bases which are loaded and unloaded accordingly. The central mechanism which is re-sponsible for the control of these procedures is composed of procedural rules.

The individual knowledge bases are also provided by central mechanisms. These mechanisms control theprocesses executed within their environment. These mechanisms can also control the behavior of the agenda(strategy). Rules within the same knowledge base can be grouped. The central mechanism can call sets of rulesinstead of individual rules in a specific sequence.

Method of portrayal

The identification of portrayal method for the chart entities, is generally dictated by a number of factors rel-evant to the chart (e.g. chart scale, chart category, congestion of chart information) as well as factors inherentto the entities themselves (e.g. entity characteristics and attributes). Chart specifications describe in detail themethod of portrayal for all entities which may be portrayed on a nautical chart at any scale. For instanceairports on medium scale charts are depicted by their outline, while in small scale by a point symbol. Someentities are portrayed with ‘simple’ symbols while others with more complex ones. Soundings are portrayedwith numbers representing their values, while lights are portrayed with the use of point symbols along with textdescribing their characteristics. ‘Knowledge’ encompassing the diversity of methods of portrayal, as well asthe way they are implemented on the chart, is also encoded in the form of rules.

The design process in the expert system environment, is initiated as soon as the cartographic entities which will beused for the composition of nautical chart are loaded and organized in the object-oriented model of the system.

The relational structure table-record-item implemented by the database management system and the geo-graphic information system,is mapped into the object-oriented structure class-ob-ject-property of the expertsystem.

Chart entities constitute ob-jects belonging to classes.The conditions under whichany entity is linked to theappropriate method of por-trayal, is expressed in theform of rules (design rules).The set of these rules containconditions which evaluateparameters like chart scaleand the particular attributesof the objects which may in-fluence their portrayal. The Figure 1. The method of portrayal selection for wrecks.


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evaluation of these conditions results to the method of portrayal. This is implemented by the attachment of theparticular entity objects to classes (design classes), where the various portrayal methods have been organized.The objects/entities inherit the methods of portrayal from the parent class. Figure 1 describes this process forwrecks.

The system in order to support the graphic conflict resolution, implements specific representations for the chartentities. Point, linear, areal and text entities are represented as follows (see Figure 2):

· Point entities are represented by their minimumboundary rectangles (MBRs)

· Linear entities are represented by the edges of theConstraint Triangular Irregular Network (TIN) whichis computed using their centerlines. The edges of thelinear entities have specific direction and attributes,such as the buffer distance

· Areal entities are represented by the triangles of theConstraint TIN which is based on their outlines. Eachareal entity is composed by the triangles which arelocated into it

· Text entities are represented by polygons accordingto their alignment. Texts aligned as straight lines (e.g.light characteristics) are substituted by their MBRs.Texts aligned along curves (e.g. toponyms) are sub-stituted by their bounding polygons

An object attached to a specific design class in order to inherit the method of its portrayal, inherits the param-eters which will enable its ‘abstract’ representation. In the case of point entities, objects inherit the relativecoordinates in respect to the bottom-left and top-right corner of the respective MBR. The bounding polygonsare computed for the text entities, while buffer distances are inherited for the individual linear entities.

Graphic conflict detection and resolution

Once the entities of the area to be charted are selected, assigned to the predefined layers and the way of theirportrayal is identified, the phase of conflict detection and resolution is executed. In general, cartographic enti-ties require more space than their actual dimensions dictate. Maps/charts also portray ‘abstract’ phenomenalike names (e.g. text descriptions, toponyms), isolines (e.g. contour, depth contours), heights or soundingswhich are not tangible and do not have real dimensions. These entities provide an additional source of graphicconstraints which are generally resolved through omission, simplification, exaggeration, combination and dis-placement, as well as combinations of them.

The interactions between point, linear, areal and textual entities may generate graphic conflicts. Entities arerepresented within the expert system environment as polygons (MBR is considered as a special case of poly-gon), edges and triangles of a constraint TIN. In order to detect graphic conflicts, the system searches for allpossible combinations among these representations. The graphic conflicts which are expected to be detectedand resolved are:

· Polygon vs. Polygon

· Polygon vs. Edge

· Polygon vs. Triangle

Figure 2. Representations of the chart entities


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· Edge vs. Edge

· Edge vs. Triangle

· Triangle vs. Triangle

The detection of graphic conflicts will be car-ried out through the evaluation of the conditionexpressions in the composition rules. This willtrigger the appropriate actions for their resolu-tion. The graphic conflict resolution methodsare organized into classes (conflict classes). Theindividual conflicts produce conflict-objectshaving as slots the characteristics of the entitiesinvolved. The conflict-object is attached by therule that has been detected to the relevant con-flict class, where from it inherits the appropri-ate methods for its resolution (see Figure 3).

The above mentioned methodology for the resolution of graphic conflicts must eliminate the possibility ofgeneration of new graphic conflicts. The cartographic products are generally characterized by the interrela-tions of the graphic entities. This creates serious difficulties to the design of a linear cartographic compositionprocess which is indispensable for the development of an ‘automated’ cartographic system. The design of alinear composition process is being considered here. The relatively ‘simple’ design of nautical charts, enablesthe drawing of guidelines which the system follows in order to resolve the graphic conflicts and create progres-sively the final image of the chart.

The land and sea parts of the nautical chart are processed separately. These two basic layers (or more preciselysets of layers) are adjoined along the coastline. The resolution of graphic conflicts among topographic/hydrographic entities is being executed in the respective areas. This approach minimizes the synthesis prob-lems of the individual sets of layers. Chart entities are organized in layers according to their individual charac-teristics. Homogeneous entities and entities which must be processed simultaneously, share common layers.The applied procedure composes first the layers which include entities belonging to the higher levels of hierar-chy and moves to the lower ones. For instance, the system first processes the layers containing navigationalaids or dangers and subsequently the layer of soundings which is more flexible in the sense that if a soundinggenerates a conflict, it may be omitted and an adjacent one may be portrayed instead. The sea part of nauticalcharts is generally organized into the following layers which are processed in accordance with the sequencethey appear:

· Coastline, depth contours

· Navigation dangers, navigation aids, ‘areas’ (e.g. restricted areas, anchorage areas, pipe areas)

· Depth Soundings

· Nature of seabed

In order one layer to be processed is ‘added’ to the already processed layer or layers. The scales of the originaldatabase and of the chart under construction, must be relevant. Small differences in scale do not lead to reallyproblematic situations and minimize the effects of generalization processes to topology.

Figure 3. Graphic conflict resolution process


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Conclusions

The efficient utilization of geographic information systems and expert systems technologies, provides promis-ing solutions to a number of cartographic problems. The procedures of design and composition of maps/chartscan be ‘automated’ to a considerable degree within the environment of a hybrid system. Expert systems pro-vide flexible mechanisms to detect and resolve conflicts, according to the designers needs. The implementationof such a system, requires a flexible and integrated application logic which must be embedded into it. Tailoringthis logic to a specific map type - the nautical chart – is considered essential due to the fact that rules effectivefor the design and composition of one map type, may not be effective for another. The knowledge base must becontinuously enhanced with new/refined rules without influencing the internal structure and operation of thesystem. The numerous situations which emerge, during the design and composition process, can be handledonly if the system is well designed and ‘complete’. This implies thorough analysis of the specific map/chartcharacteristics and identification of all types of constraints (structural, graphic, application, procedural) inher-ent to the specific map/chart product. Specifications for nautical charts along with its high level of standardiza-tion, constitute a sound background for the design and implementation of the system. Without ignoring theinherent difficulties and taking into account the results and experiences gained so far, we believe that such asystem is not far from its materialization.

References

Brassel, K.E., and Weibel, R. (1988). A review and conceptual framework of automated map generalization. Interna-tional Journal of Geographical Information Systems, 2(3), 229-244.

Forrest, D. (1995). Don’t break the rules or helping non-cartographers to design maps: An application for cartographicexpert systems. Proceedings, 17th International Cartographic Conference, Barcelona, Spain, 570-579.

Freeman, H., and Ahn, J. (1984). AUTONAP - an expert system for automatic name placement. Proceedings, 1st Inter-national Symposium on Spatial Data Handling, 544-569.

I.H.O. (1996). IHO transfer standard for digital hydrographic data. Edition 3.0, International Hydrographic Bureau,Monaco.

Smith, T.R., and Jiang Y. (1991). Knowledge-based approaches in GIS. In D.J. Maguire, M. Goodchild, and D.W.Rhind (Eds.). Geographical Information Systems. Principles and applications. John Wiley & Sons, New York.

Tsoulos, L., and Stefanakis, K. (1997). Sounding selection for nautical charts: An expert system approach. Proceedings,18th International Cartographic Conference, Stockholm, Sweden, 2021-2029.


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Croatian State Boundary at the Adriatic Sea

Ivka TunjicUniversity of Zagreb, Faculty of Geodesy, Kaciceva 26, 10000 Zagreb, CroatiaE-mail: [email protected]

Miljenko LapaineUniversity of Zagreb, Faculty of Geodesy, Kaciceva 26, 10000 Zagreb, CroatiaE-mail: [email protected]

Abstract

The increased possibilities of geographic information systems in spatial data management require repeatedauditing of basic presentations and measurements in spatial analyses. The paper explains the geometric way ofdetermining the outer boundary of the territorial waters. The applicability of Gauß-Krüger projection hasbeen tested in solving the given problem in the plane. The practical application of the suggested methods hasbeen illustrated in the example of the outer boundary of Croatian territorial waters.

1. Introduction

The majority of answers referring to the maritime boundary contains a statement that the “straight lines” willbe used for connecting the set of points which are given by geographic coordinates. This is one of the omis-sions that can lead to various interpretations. One should namely distinguish between the geodesics, greatcircle and loxodrome [Thamsborg, 1974]. The “distance” is for the seaman the arc length of loxodrome, but fora surveyor it is most often the length of the geodesics.

Since the maritime chart is based on the map projection, the nature of the straight line depends on the geometri-cal properties of the projection. Baezley [1982] has noticed that the Mercator projection is not very convenientfor the determination of distances, but he does not say which projection it might be. Carrera [1987] deals withthe method of delimitation with equidistant boundaries between coastal states. Mayer et al. [1992] suggest theapproximate method of determining the length of the geodesics by applying them to the maritime boundaries.From the cartographic and geodetic point of view, the most contents about the problem of the maritime bound-ary determination can be found in the book of Maling [1989].

In this paper the method for the determination of the line at the given distance from the given line at sea issuggested. One can say, that it is a modified and automated version of Shalowitz method [1962]. The researchhas included the estimation of the deviation of geodesics and loxodrome from the straight line in the particularexample of the Croatian maritime boundary determination in the Adriatic Sea.

In practice, when drawing the outer boundary of the territorial sea, one of the two following methods is ap-plied, or their combination (see Figure 1):

a) Parallel line method (tracé parallèle in French). A line determining the outer limit of the territorial sea isdrawn parallel to the baseline. This method can be applied when the coastline is relatively straight.


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b) Method of envelopes of arc of circles (méthodede la courbe tangente in French). The arcs ofcircles are drawn with the centres at the mostforward positions of land and with the radiusthat corresponds to the territorial sea breadthof the coastal state. Then, the outer parts ofthe arcs of circles, between the points of inter-sections with the neighboring arcs, representthe outer limit of the territorial sea.

At the end of the introductory part of this article,we would like to give some remarks. When talk-ing about a straight line or a circle, then it shouldbe clear that such objects generally do not existon a sphere or ellipsoid. On the other hand, ifone thinks of the representation in a plane, thenthe name and parameters defining the used mapprojection should be stated. Namely, it is wellknown that the properties of map projections re-garding the distortions of lengths, angles and areaare quite different. Regarding the methods ofenvelopes of arcs, shown at Figure 1A, one cansee that the choice of centres of circles has beenroughly estimated and probably could be refinedin some way. The parallel line (see Figure 1, Band C) is rather disputable because one don’tknow why the distance has to be measured inthe shown direction, and not in some other di-rection where the distance will be completelydifferent!

2. Method of perpendiculars or arectangle on a sphere

When talking with colleagues about the deter-mination of the outer limit of the territorial sea as a line whose each point has a property that the distance to theclosest point at the baseline is equal to the coastal state territorial sea breadth, one can usually hear that it issimple problem which can be solved by drawing the perpendiculars to the baseline. In this Chapter we willshow that it is not true. Namely, if the earth would be flat, then the problem will be really simple, and it couldbe solved by drawing the appropriate perpendiculars to the baselines. However, due to the earth’s curvature theproblem has to be solved directly on the sphere or ellipsoid, or in the plane of projection. Let us consider arectangle. It is a four-sided polygon in a plane with four right angles and its opposite sides are of equal length.

Now, let the perpendiculars AC and BD be drawn to the straight line segment AB in a plane and at the same sideof the segment (see Figure 2). If the segments AC and BD are of equal lengths, then ABDC is a rectangle, andthe length of CD is equal to the length of AB. This is known to everybody from the basic mathematics.

Figure 1. Determination of the outer limit of the territorialsea: A – method of arcs; B and C – method of drawing aparallel line to the straight baseline (B) and to the normalbaseline when the coastline is relatively straight (C); ac-cording to [Rudolf, 1985]


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Let us try to do the same on a sphere instead of doing it in the plane. For this purpose, let us take a unit sphere withgeographical coordinates f and � on it. Let AB be the arc of an orthodrome or great circle, e.g. equator, and let itslength be �� (se Figure 2). At the end points of arc AB let the perpendiculars AC and BD be drawn. If the lengthof arcs of orthodroms AC and BD are equal, then ABDC is not a rectangle because the length of arc of orthodromeCD is not equal to the length of arc of equator AB, and the angles ACD and BDC are not right angles.

Figure 2. Rectangle ABDC in a plane and “rectangle” ABDC on a sphere

The previous statement is a little bit unusual, or at least it is not obvious. Therefore, it has to be proved. Iinorder to do so, let us denote the following points A(0, �1), B(0, �2), C(�1, �1), D(�1, �2). Let the length of arc oforthodrome from the point C to the point D be ��

T1(�1, �1) and T2(�2, �2) can be computed by using formula [Lapaine, 1997]:

(1)

and in our case the length of the arc CD is

(2)

or after the appropriate trigonometric transformation

(3)

From the last relation one can see that it is ��1=0 or ��ABDC degenerates in an arc. In that way we proved that the length of the arc CD of orthodrome is generallyalways smaller than the length of the arc AB of orthodrome. Now we are going to show that the angles ACDand BDC can not be right angles.

It is known that the angle �� T1(�1, �1) and T2(�2, �2) andthe meridian passing through the point T1 is given by the expression [Lapaine, 1997]:

(4)where

(5)

(6)

λ∆ϕϕ+ϕϕ=σ coscoscossinsincos 2121

,coscossincos 12

12 λ∆ϕ+ϕ=σ

.2

sinsin2coscos 21

2 λ∆ϕ+λ∆=σ

,costancostan

sintansintantan

1221

1221

λϕ−λϕλϕ−λϕ

=β

.)cos(tantan2tantan

)sin(

212122

12

21

λ−λϕϕ−ϕ+ϕ

λ−λ=k

,1

)cos(cos

2

1

+

β−λ=γ

k


12 Index

If the orthodrome is going through the points C and D, then after substituting their coordinates in (5) and (6),the appropriate transformations can give the following:

(7)

(8)Substituting the expressions for !��k from (7) and (8) in (4), after some manipulations one can get therelation

(9)

From the last formula (9) one can see that the angle ��

C is the right angle, if and only if it is �1=0o or ��o. These are special cases when the four-sided curved

polygon ABDC degenerates in an arc. If it is for instance ��"�o, then it is ,3/1cos =γ for �1=45o, while

for �1=60o, it is .5/1cos =γ If it is for instance ��#$�o, then for any �1, it is cos ��#��o, which

means that in curved polygon ABDC two angles are 90o, and the two other 180o (see Figure 3)!

,22

21 π−λ+λ

=β

.2

coscot 1λ∆ϕ−=k

.

sin2

cot

sincos

122

1

ϕ+λ∆ϕ

=γ

From the previous elaboration it can be concluded that there are no rectangles on a sphere in the way we areused to it in a plane. On the sphere a “rectangle” ABDC can have two neighboring right angles and twoopposite sides of equal length, but two remaining angles generally will not be right angles and the other twosides will not be of equal length.

Figure 3. “Rectangle” on a sphere having two Figure 4. “Duality” of the right angle

right and two straight angles

According to that, if one moves from the point A belonging to an orthodrome and goes along a great circlemaking a right angle with the first orthodrome, then he will arrive to the point C belonging to some otherorthodrome (see Figure 4). If he moves back going from the point C along the great circle that is perpendicularto the orthodrome passing trough the point C, he will not come back to the point A. In other words, on thesphere there are no parallel “straight lines” at all.


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3. Territorial sea of Croatia

It is a surprising fact that, out of the 22 independent states which have been created since 1990, 11 are land-locked. Of the remainder, some have relatively short coastlines. Croatia is one of the most fortunate in terms ofthe length of coastline although the large number of Croatian islands makes comparison difficult. This coast-line is without question one of Croatia’s most important assets, which will have to be carefully managed andprotected [Blake, 1994].

The use of straight baselines is in international law permitted where coasts are highly indented, or fringed withislands. They are important as the baseline from which the width of the territorial sea is measured. Baselinesalso enclose internal waters, in which the coastal state enjoys the same extensive rights of sovereignty as onland.

Former Yugoslavia was one of the first states to adopt straight baselines in 1948. This system of straightbaselines was extended in 1965 to an almost continuous line, and has been praised by commentators as a modelof a modest and correctly applied straight baseline. Many states in the world have made exaggerated claims tostraight baselines, contrary to the guidelines in Article 7 of the 1982 Law of the Sea Convention. Yugoslavia’sbaselines have never been disputed by other states, and Croatia continues to apply the same baselines.

The 1982 Law of the Sea Convention entered into force on 16th November 1994, and Croatia joined it on 5thApril 1995.

Croatian Maritime Code determines the Croatian sea and seabed in details, organises safety of navigation,material and law relationships, etc. The Croatian baselines are defined in the Article 19 of the Croatian Mari-time Code [1994]:

1) lines of average low waters along the cost of land and islands,

2) straight baselines closing the entrances in ports and bays,

3) straight baselines connecting the following points at the coastlines:

a) cape Zarubaca – SE cape of island Mrkan – South cape of island Sv. Andrija – cape Gruj (island Mljet),

b) cape Korizmeni (island Mljet) – island Glavat – cape Struga (island Lastovo) – cape Velje more (islandLastovo) – SW cape of the island Kopiste – cape Velo dance (island Korcula) – cape Proizd – SW cape of theisland Vodnjak – cape Rat (island Drvenik mali) – rock Mulo – rock Blitvenica – island Purara – islandBalun – island Mrtovac – island Garmenjak veli – the point at the island Dugi otok having the coordinates43o53’12"N, 15o10’00"E,

c) cape Veli rat (island Dugi otok) – rock Masarine – cape Margarina (island Susak) – shoal Albanez – islandGrunj – rock Sv. Ivan na pucini – shoal Mramori – island Altiez – cape Kastanjija.

The baselines are drawn in the maritime chart S101 Adriatic Sea, the northern and the middle part, publishedby the State Hydrographic Institute (first edition on 1st March 1971, then supplemented editions in 1973, 1980,1986, 1990, 1996).

The Croatian territorial sea spreads from the straight baseline towards the continental shelf boundary up to thedistance of 12 nautical miles (1 nautical mile = 1852 m). In its southern part, the territorial sea is measuredfrom several islands (Jabuka, Svetac, Palagruza etc.), and not from the straight baseline. At the places wherethe straight baseline is not drawn the territorial waters are measured from the low water mark along the coast.The outer limit of the territorial sea is the line that has each point 12 nautical miles away from the nearest pointof the baseline.


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4. Gauß-Krüger projection

The official map projection for the territory of former Yugoslavia was Gauß-Krüger projection by means ofwhich the entire state territory was mapped in three zones. Prof. N. Francula from the Institute for Cartographyat the Faculty of Geodesy, University of Zagreb has suggested the Gauß-Krüger projection for the maps of theentire Croatia at the scale of 1:300 000, or smaller, with the central meridian 16o30’E (Francula 1973, 1981). Inorder to reduce the linear distortions, the linear scale 0.9997 has been introduced on the central meridian.

The question is raised whether the same projection could be applied in the determination of the outer boundaryof the Croatian territorial sea. This question will be answered in the next Chapter.

5. Replacement of a geodesics or loxodrome with a straight line

In order to examine the possibility of replacing the geodesics image with the portion of the straight line, threepoints have been chosen. The point T

1 lies in the northern part of the Adriatic Sea, point T

2 in the middle, and

point T3 in the southern part of the Adriatic Sea (see Figure 5). The circles with the radius of 12 nautical miles

are delineated around the images of these points in Gauß-Krüger projection. On each of these circles 180equally arranged points have been selected. For these points their geographic coordinates have been computed.Then, it was possible to compute the length of the geodesics on the Bessel’s ellipsoid from a single point of thecircle to the corresponding centre.

The analysis of the obtained results shows that the difference between the length of the geodesics on theellipsoid and the length of the straight line in the plane of projection never goes over 10 m (see Figure 6). Thesame conclusion can be made after applying the formula for computing the linear distortion d that is defined as

(10),1−=ds

dSd

where dS is the infinitesimal linear element in the plane of projection, and ds corresponding linear element onthe ellipsoid. According to Borcic (1976), there is in Gauß-Krüger projection:

(11),1242

14

4

2

2

0 −

++=

R

y

R

ymd

where the linear scale on the central meridian for the selected projection is m0=0.9997, R the mean radius of the

ellipsoid at a point, and y the ordinate of the observed point. Although the previous formula gives the amountof the linear distortion in the point, this formula can be used also for the computing the linear distortion ofrelatively short segments. R and y can thereby be taken in the middle point of the segment.

From the performed research it can be concluded that if we are satisfied with the accuracy of 10 m, then a partof the straight line can be used instead of the geodesics in the selected Gauß-Krüger projection. We shallfurthermore take this as a presumption, and thus have the possibility of solving the problem in the plane.

A similar procedure has been done with a loxodrome in place of geodesics. The results show that for thedistance of 12 NM the length of geodesics and the length of loxodrome differ less than 0,01 m that is certainlynegligible regarding the error introduced by map projection. This result was confirmed by computing the mostremote point of loxodrome from orthodrome. The computation was based on the formulas derived by Viherand Lapaine [1998] and showed that the most remote point of loxodrome from an orthodrome between twopoints at the distance of 12 NM never goes over 10 m. Therefrom it can be concluded that in the frame of givenaccuracy, and in the selected Gauß-Krüger projection there are no differences between a geodesics and aloxodrome. That means that we are able to perform further geometrical research in a plane.


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Figure 5. The circles in the Gauß-Krüger projection Figure 6. Residuals of geodesics lengths in threefrom 12NM points on the ellipsoid surface

6. Mathematical definition of the territorial sea boundary

On the basis of the previous explanations we can give an abstract definition of the territorial sea boundary. Weshall say that G is the boundary of the territorial sea with the width d of some set A in the plane if for each pointT belonging to the boundary G there is a point P from the set A so that the distance between the points T and Pis equal d. More precisely,

(12){ }{ }dAPPTdTdAG =∈= ),(min),(

Thereby d(T, P) means the euclidean distance between the points T and P.

Figure 7. Boundary G of the territ. sea of the point A Figure 8. Boundary G of the territ. sea of the linesegment A

When the baseline would consist of only one point A, then the boundary G of the territorial sea would be thecircle with the centre in the point A and with the radius d (see Figure 7). If the baseline is the line segment A, theboundary G of its territorial sea is the curve consisting of two semi-circles and two straight line segments (seeFigure 8). If the baseline is a polyline A composed of two line segments, as shown in the Figure 9, then theboundary G of its territorial sea is more complex and consists of two semi-circles, one circle arc and fourstraight line segments.


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Let us imagine that the baseline A is the polyline consisting of a larger number of segments. The boundary Gof its territorial sea will consist of circle arcs and straight line segments. Circle arcs have the centre always inthe breaking points of the baseline and the radius d. The parts of the boundary G that are straight lines segmentsare located at the distance d from a single segment of the baseline.

Figure 9. Boundary G of the territorial sea of the polygonal line A

A geographic information system (GIS) is a system for capture, storage, retrieval, analysis, and display ofspatial data. A GIS usually enables to develop topologies, which means a series of defined relationships be-tween nodes, links, and polygonal regions. This information can be analysed to provide data on spatial rela-tionships. Topologies are also a very efficient way to store polygonal or area-based data.

Using buffer analysis, or buffering, one can easily identify objects within a specified offset of elements innode, network, and polygon topologies. A buffer is a zone that is drawn around a topology. For example, onecan specify a buffer on either side of a river to show the extent of a flood plain. By specifying a buffer offset anew polygon topology is created from an existing node, network, or polygon topology.

To conclude, the determination of territorial sea limit can be interpreted as a construction of a buffer of a givenwidth around a network topology made of polygons representing the baselines of a state.

7. Construction of the territorial sea boundary of Croatia by using network topology

As it has already been stated in Chapter 2, the Croatian Maritime Code brought in 1994 defines in its 19 Articlethe baseline as well. However, this definition is of a descriptive character and as such inconvenient for compu-tations. Since we have not received the list of the coordinates of the baseline points from the state institutions,we have taken them from the diploma thesis (Javorovic, 1993). The list was made by digitising the map S101Territorial Sea Boundary of SFRJ and the Republic Italy, and the forbidden areas along the Yugoslav coast atthe scale of 1:650 000 in Mercator projection. Knowing the standard parallel of the used Mercator projection,it was possible to compute the belonging geographic coordinates with regard to the Bessel’s ellipsoid.

The list of coordinates makes a discrete record of the baseline. By applying direct equations of any projection,this baseline can be drawn. We have used known equations of the Gauß-Krüger projection with the scale on thecentral meridian m

0=0.9997 (see Chapter 4). Coastlines of Croatia and Italy and the islands in the Adriatic Sea

have been acquired analogously in a few seminars and diploma thesis by digitising from the maps at the scaleof 1:1 000 000 to 1:50 000. For the official purpose of determination of outer limit of Croatian territorial sea,one will need to have better numerically defined Croatian baselines.

Our list of points of the baseline together with a few islands located separately (see Figure 10), contains 850points. Drawing the territorial sea boundary manually, by using the definition from the Chapter 6, would really


12 Index

be rather hard work. In a previous paper (Tunjic, Lapaine 1998) the method of solving the entire problem byusing AutoCAD has been described.

Figure 10. Croatian baselines and the application Figure 11. Croatian baselines and the outer limit ofof network topology with the the Croatian territorial seaappropriate buffer

Due to the AutoCAD Map (Autodesk, 1997), a mapping version of AutoCAD, the whole story can be short-ened. By creating the appropriate network topology and defining a buffer with 12 NM width, AutoCAD Mapdraws the buffer presented in the Figure 10 in a few seconds. Hence, simply by erasing the unnecessary partsone can easily come to the final solution (see Figure 11).

References

Autodesk (1997). AutoCAD Map, Release 2, Using AutoCAD Map, User’s Guide.

Baezley, P. B. (1982). Maritime Boundaries, International Hydrographic Review, Vol. 59, No. 1, 149-159.

Blake, G. (1993/94). Croatia’s Maritime Boundaries. In: Croatia – a New European State, Proceedings of the Sympo-sium held in Zagreb and Cakovec, 1993, Department for Geography and Spatial Planning, Faculty of Science,University of Zagreb, 39-46.

Borcic, B. (1976). Gauß-Krüger Projection of Meridian Zones (in Croatian), University of Zagreb, Zagreb.

Carrera, G. (1987). A Method for the Delimitation of an Equidistant Boundary Between Coastal States on the Surfaceof a Geodetic Ellipsoid, International Hydrographic Review, Vol. 64, No. 1, 147-159.

Francula, N. (1973). Mathematical Basis and Numerical Procedures in the Map Production of SR Croatia at the Scale of1:1000 000 (in Croatian), Symposium Cartography in Spatial Planning, Ljubljana, A4/1-9.

Francula, N. (1981). Application of Computers in the Map Production of SR Croatia (in Croatian), Faculty of Geodesy,University of Zagreb, Zagreb, Proceedings, Series D, Volume 2.

Javorovic, I. (1993). Digital Map of Waters of Croatia and Bosnia and Herzegovina (in Croatian), Diploma thesis,Faculty of Geodesy, University of Zagreb.

Lapaine, M. (1997). Vector Analysis (in Croatian), University of Zagreb, Faculty of Geodesy.

Maling, D. H. (1989). Measurements from Maps, Principles and Methods of Cartometry, Pergamon Press, Oxford, NewYork.


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Maritime Code (in Croatian), Narodne novine No. 17 of 7 March 1994, 404-503.

Mayer, F., Szychta, D., Cravacuore, M., and Veron, D. (1992). Algorithm for the Calculation of Geodetic Distances forMaritime Jurisdictional Boundaries, International Hydrographic Review, Vol. 69, No. 1, 133-141.

Rudolf, D. (1985). The International Law of the Sea (in Croatian), JAZU, Zagreb.

Shalowitz, A. L. (1962). Shore and Sea Boundary, U.S. Dept. of Commerce, Coast & Geodetic Survey Publication 10-1, 2 Vols. Washington, Government Printing Office.

Thamsborg, M. (1974). Geodetic Hydrography as Related to Maritime Boundary Problems, International HydrographicReview, Vol. 51, 157-173.

Tunjic, I., and Lapaine, M. (1998). Croatian State Boundary at the Sea, 8th International Conference on EngineeringComputer Graphics and Descriptive Geometry, Austin, Texas, Proceedings, Vol. 3, 716-720.

Viher, R., and Lapaine, M. (1998). The Most Remote Point of Loxodrome from Orthodrome (in Croatian), Geodetskilist, Vol. 52 (75), No. 1, 13-21.


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Production of Thematic Nautical Charts and Handbooksfor the Sea Area of the Eastern Adriatic Coast

Slavko Horvat, Zeljko ZeleznjakMinistry of Defense,Zvonimirova 4, 10 000 Zagreb, CroatiaPhone: +3851 4567426, Fax: +3851 4567973,e-mail: [email protected]

Tea DuplancicHydrographic Institute of the Republic of Croatia,Zrinsko-Frankopanska 161, 21 000 Split, CroatiaPhone: +38521 361840, Fax: +38521 47242,e-mail: [email protected]

Abstract

This paper briefly reviews the maritime hydrographic and nautical cartographic activities in the Republic ofCroatia through history and nowadays, especially considering the production of thematic nautical charts andhandbooks for military purposes.

1. INTRODUCTION

The Adriatic Sea is an elongated basin (ca 800 km long and 200 km wide). The northern part of the basin is aconcave-shaped shelf, whose maximum depths (around 280 m) occur in the Jabuka Pit. The bottom rises atPalagruza Sill (130 m), then deepens in the southern part – the South Adriatic Pit – to about 1200 m, and risesagain in the Otranto Strait (780 m). The western coast of the adriatic Sea is smooth, isobaths run parallel to it,and depth increases gradually seaward. The eastern coast is composed of many islands and headlands risingabruptly from the deep coastal water.

A thousand islands and more than 5000 km of coastline, numberless straits, passages and other areas danger-ous for navigation along the east coast of the Adriatic Sea, causes this area to be an exceptionally complexnavigational whole. Adriatic subsea topography, as a part of the macrotectonic origin subsea valley betweenthe Apennines, Alps and Dinarides.

Such area needs constant hydrographic and oceanographic survey, as well as production of high quality nauti-cal charts, handbooks and publications, and various thematic charts and handbooks.


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2. SHORT HISTORICAL REVIEW OF HYDROGRAPHIC AND CARTOGRAPHICACTIVITIES

Organized and systematic hydrographic and nautical chart production for the east coast of the Adriatic Sea hasa long tradition. French hydrographer Charles – François Beautemps Beaupré performed the first hydrographicsurvey along the east coast of the Adriatic Sea (Figure 1). From 1806 to 1809 during his campaign, he surveyedthe most significant Croatian harbours, performing also astronomic, geodetic, hydrographic and geomagneticmeasurements. An atlas with 15 maritime plans and 2 panoramas was given as the result of this campaign(Duplancic, 1999).

Figure 1. – A part of Beautemps Beaupré’s maritime atlas

During the campaign from 1822 to 1824 Austro – Hungarian Navy performed a systematic survey of the eastcoast of the Adriatic Sea. The result of campaign were 2 general charts, 22 sailing charts and 7 harbour pano-ramas. The Kingdom of Austria – Hungary established the first Hydrographic Office in Trieste during 1861,which moved to Pula the next year. Since then till nowadays hydrographic service has had almost a century anda half of continuous activity (with breaks during world wars) over the east coast of the Adriatic Sea. Over 1000hydrographic originals on different scales in Gauss – Kruger’s projection according Bessel 1841 were pro-duced during that period of time.

Few hydrographic institutions could boast such a long hydrographic, oceanographic and cartographic activi-ties. From 1991 hydrographic service take place in Hydrographic Institute of the Republic of Croatia (HHI).

3. HYDROGRAPHIC AND CARTOGRAPHIC ACTIVITIES NOWDAYS

Nowadays, hydrographic survey uses integrated hydrographic systems with DGPS positioning methods, whichprovides exceptional accuracy. Specific topography of the sea bottom is given by side-scan sonar image cor-rection survey, as well as multibeam technique survey. Hydrographic information system – HIDRIS is used to


12 Index

collect and process the collected hydrographic and oceanographic data. Hydrographic survey data are partlymeasured in the local coordinate system and partly in WGS 84.

Solution for all cartographic activities, for civil maritime economy as well for the Croatian Navy, are certainlythe existing interactive computer graphical systems within HHI, with modern hardware / software equipment.Wide cartographic data bank, analogue and digital, is the basis of cartographic information system – CIS.

Croatian Hydrographic Institute covered the Adriatic Sea with 8 general charts (scales from 1:750 000 to 1:2500 000), 30 sailing charts (scales from 1:150 000 to 1:300 000), 21 coastal charts (scales from 1:50 000 to1:100 000), INT charts (scales 1 : 250 000) and various plans on scales 1:3 000 to 1:40 000 in several editionsand publications. Apart from nautical charts this Institute provides numerous different informative, auxiliaryand special thematic charts.

Cartographic activity, apart from new analogue and digital chart production, proceeds in several mutuallyconnected directions: transfer of all analogue charts to digital form, digitalization of hydrographic originals,cartographic data bank production, IHO’s recommendation standardization for display on charts, solving prob-lem of incompatible nautical charts of HHI’s production towards the neighbouring countries nautical chartproduction. These are the significant steps nowadays.

4. MILITARY CARTOGRAPHIC SYSTEM PRODUCTION

C3I (Command Control Communication and Intelligence) system optimized a quantity of information on theAdriatic Sea area. The developed military hydrographic – cartographic information system essentially followsand processes battle activities, using the most advanced computer technologies (Horvat, 1992).

At the moment, the production of this system is in the phase of initialization. New maritime navigation charts,publications and handbooks are produced in digital form together with formerly published nautical charts andpublications, which are to be slightly modified and involved in the system.

For military purposes HHI produces special charts in analogue and digital form, as well as various handbooksand other products such as: navigational handbooks, nautical – topographic charts scaled 1: 25 000, rastersystem of coastal, sailing charts, plans and sedimentologic charts of the Adriatic Sea.

4.1. NAVIGATIONAL HANDBOOK

Navigational handbook is produced both in analogue and digital form. Handbook is the result of systematicdata collection in the hydrographic, oceanographic and nautical survey, as well as cartographic processing ofthe collected data. Handbook displays all harbours and marinas, most of the bays, anchorages, quays, berthingfacilities and other navigational objects within Croatian part of the Adriatic Sea.

Besides graphical display handbook includes the data necessary to get the knowledge of local characteristics:orientation, meteorological data, currents, sea transparency, high and low waters, possibilities of entering ports,mooring and anchoring possibilities, repair service, coastline descriptions, offshore coastline description, strand-ing points, food and water supply, medical insurance, travel guide to neighbouring places, harbour installations(cranes, dock entrances, workshops), heights of quays and other data.

4.2. NAUTICAL – TOPOGRAPHIC CHARTS, SCALE 1 : 25 000

For areas of special navigational interest, HHI produces nautical – topographic charts, scaled 1:25 000. Detaildisplay of land contents on these charts uses standards valid for topographic chart production, as well assymbols valid for topographic contents. Nautical contents are displayed with details according to rules that are


12 Index

valid for nautical chart production, with the symbols used on nautical charts.

Till now, 12 of the planned 37 charts have been produced in analogue form (Figure 2). These nautical - topo-graphic charts are produced on Gauss – Kruger’s projection, according to Bessel 1841 data. Formerly pro-duced charts have been modified by overprinting the cartographic grid in magenta, according to WGS 84. Newcharts are produced in vector form with the cartographic grid within the state coordinate system and accordingto WGS 84.

Figure 2. – Part of maritime – topographic chart

4.3. SEDIMENTOLOGIC CHARTS

The features and structure of the Adriatic seabed are not sufficiently displayed on sedimentologic charts asrequested by economic, scientific, military and other reasons (Juracic, 1993). For the entire Adriatic Sea area,sedimentologic chart scaled 1 : 1 000 000 was produced as well as on four leafs scaled 1 : 750 000. Fornavigational areas of special interest, 10 charts scaled 1 : 100 000 and 1 : 25 000 are produced in Gauss –Kruger’s projection in analogue form (Figure 3).


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Figure 3. A part of sedimentologic chart

4.4. NAVIGATION CHARTS IN RASTER FORM (RCDS) PRODUCTION

Due to limited funds for ECDIS production, as a transitional stage for military purposes a system of nauticalcharts in raster form (RCDS) is being developed. The existing INT charts, sailing charts scaled 1: 300 000,coastal charts scaled 1: 100 000 and 1: 50 000, sedimentologic charts scaled 1: 100 000 and 1: 25 000 as wellas plans are scanned with 127 dpi resolution and geocoded, e.g. transferred from Mercator’s projection toGauss – Kruger’s projection.

5. CONCLUSION

Hydrographic and cartographic activity in the Republic of Croatia has a long tradition. The existing nauticalcharts, publications and handbooks provide safe navigation and help in carrying out other activities within theCroatian part of the Adriatic Sea, also representing the base for the ECDIS military command system produc-tion, as well as for production of other projects.

In the following period, full implementation of the standards in hydrographic and cartographic activities ac-cording to the IHO and IMO recommendations is planned.


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REFERENCES

Canadian Hydrographic Service (1997): S - 57 ENC Product Specification, Version 1.1, CHS,

Duplancic, T. (1999): Electronic charts in nautical cartography, M.Sc. Thesis, Geodetski fakultet Sveucilista u Zagrebu,Zagreb (in Croatian).

Horvat, S. (1992): Digitalization of hidrographics originals as basis for formating digital cartographic data base, M.Sc.Thesis, Geodetski fakultet Sveucilista u Zagrebu, Zagreb (in Croatian).

IHO (1990): Chart Specifications of the IHO and Regulations of the IHO for International (INT) Charts, InternationalHydrographic Organization, Monaco.

IHO (1994): Hydrographic Dictionary – Special Publication No.32, V Edition, International Hydrographic Organiza-tion, Monaco.

IHO (1996): Specifications for Chart Content and Display Aspects of ECDIS, International Hydrographic Organiza-tion, Monaco.

IHO (1997): Glossary of ECDIS – Related Terms, III Edition, International Hydrographic Organization, Monaco.

Juracic M. (1993): Prolegomena za izradu geoloskih karata dna Jadranskog mora, Vijesti Hrvatskog geološkog drustva,Vol. 30, No. 2, Zagreb.

Vidovic, B. (1998): Automatization of activities in complex data bases, M.Sc. Thesis, Fakultet elektrotehnike i racunarstvaSveucilista u Zagrebu, (in Croatian).


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Session / Séance 06-A

The use of global mathematical models in the cartography of marinesandbanks

Tom Vande WieleRUMACOG - Research Unit for Marine and Coastal GeomorphologyUniversteit GentVakgroep GeografieKrijgslaan 281 - S89000 GentBelgiumE-mail : [email protected]

Abstract

For the mapping of sandbanks we will make use of global mathematical models. The general models availableare the trendsurfaces (algebraic) and the double Fourier series (trigonometric).

The justification why to use these models falls within the framework of a general research on the influence ofpoint patterns on different models for the representation of the relief of submarine sandbanks. Our hypothesesstates that these global methods are less subject to the influence of certain point patterns with as result thatthese models can serve as a base for a further mapping. A second justification is that there is always a generaltrend in the data, which can be described by global models.

For the interpretation of these mathematical methods we state that the deviations with respect to the model aresignificant and thus represent a local component. This gives the opportunity to map the differences betweenthe data and the model with local methods, like the classical interpolation models.

The research module now tries to determine to which extent the models can be used for mapping, whereby theinfluence of certain settings are examined. By settings we not just mean parameters as the power of theequation (in the case of trend surfaces) or the number of terms in the series or the fundamental wavelengths (inthe case of double Fourier series), but also the orientation of the axis and the size of the research area (thiswith respect to the possible edge effects).

One of the tools we will use to test the effectiveness of the model is the semivariogram. Thereby we foresee thepossible use of kriging as the local interpolation technique. When the global methods enable us to predict thetrend, then a simplification of the semivariogram (with zonal and geometric anisotropy) must be the result.This was one of the obstacles to use the kriging technique for mapping the submarine sandbanks.

Double Fourier Series

A function can be approximated by an infinite trigonometric series. If we consider the relief as an unambigu-ous finite continuous and periodic function of x and y, then the following equation can be used for the represen-tation of that relief.


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Zn x m y

n x m y

n x m y

n x m y

ij nmi j

mn

nmi j

mn

nmi j

mn

nmi j

=

∑∑

+

∑∑

+

∑∑

+

=

∞

=

∞

=

∞

=

∞

=

∞

=

∞

απλ

πλ

βπλ

πλ

γπλ

πλ

δπλ

πλ

cos cos

cos sin

sin cos

sin sin

2 2

2 2

2 2

2 2

1 211

1 211

1 211

1 2

∑∑

=

∞

=

∞

mn 11

The unknown parameters are the fundamental wavelengths λ1 and λ

2, together with the coefficients α

nm, β

nm,

γnm

and δnm

. To put this theory into practice, some simplifications and approximations are necessary. Thismeans among other things that the fundamental wavelengths are approximated by the distances L

1 and L

2,

which makes it possible to avoid the repeating behavior by choosing these distances greater than the selectedarea of study. A second, obvious, approximation concerns the number of terms of the series. This has a directeffect on the necessary computing time.

Two important questions arise now. First, how do we adapt our data to the equation, and secondly how do weinterpret the deviations from the calculated equation ?

Concerning the first question, we will make use of the least square method, which states that the square devia-tions must be minimal. As for the interpretation, we consider that the deviations from the equation are com-posed of a significant local component and a small error component.

( )z f x y Li T i i i i= + +, ε

The data.

The area of study is situated before the Belgian coast. It is part of the Kwintebank, which forms part of theFlemish Banks. The sandbank is characterized by his asymmetric form, steepest slope faced NW, and theoccurrence of sandwaves and megaripples.

The data acquisition is performed with the research vessel Belgica by making use of the Sercell DGPS posi-tioning system and the Deso 20 echosounder in combination with the TSS heave compensator.

The data itself exists out of 60 SW - NE oriented tracks and 30 NW - SE oriented tracks. The distance betweenthe tracks is about 50 m while the distance between points on the track amounts to about 2.5 m. Besides thisdata set for the construction of the model, we also have a data set for testing the model performances. This dataset is obtained during a sediment survey in the same area. Because a sediment survey is performed at a muchlower speed the distance between two successive data points is only 0.9 m.

Out of the first data set, different patterns can be derived. The first parameter we will make use of to distinctthe different patterns, is the orientation. In this way we can derive two main patterns, according to the directionof the tracks sailed and a third one as a combination of the two preceding patterns.

The second parameter that can be used is the distance between the tracks, this is achieved by a systematicreduction of tracks in the pattern.


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Hypothesis and method.

The parameters we want to examine with regard to the Double Fourier Series model, consists of model proper-ties (like n, m, L

1 and L

2) as well as the properties of the data set used for the calculation of the best fitting

equation.

Figure 1. Hypothesis.

The diagram shows a test method and a test set. The latter we described already in the previous paragraph. Thetest method will now compare the values predicted bythe model with the observed values in the test set. Thepredicted values are acquired by importing the x, y -coordinates into the model.

Results and analyses.

The first results include a comparison between the dif-ferent patterns and this in function of the number ofFourier coefficients. To get an overall impression onthe model performances we have chosen to usePearson’s product moment correlation. This coeffi-cient gives the correlation between the predicted val-ues by the model and the observed values. This firstgraph compares 3 patterns (differing in distance be-tween tracks) based on SW - NE oriented tracks.

As we expected, the use of more terms leads to a better performance. And secondly there seems no influenceof the pattern on the results. These conclusions can also been drawn for the other oriented patterns.

This could lead to a rather rash conclusion about the influence of the point pattern. The influence of thepatterns is not shown as a model improvement but acts on the stability of the model. This can easily be provenby the next diagram which shows the same results, but now with more (10 x 10) terms used.

Figure 2. r-correlation pattern 1.


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Here we can see when the modelbecomes unstable. This phe-nomenon is related to the dis-tance between the tracks, thegreater this distance is, thesooner the instability occurs.We can also remark that com-bining the two track directionsresults in a positive effect on thestability of the model.

Like I mentioned in the begin-ning of this paper, we have todo with a best fitting equationor surface. This means that theperformance can’t decrease withan increasing number of terms.Why this occurs anyway has todo with the test set used. If welet the model predict the datathat has been used for the cal-culation of the equation (theconstruction set) and plot theseresults together with those ob-tained by the test set, then thedifference between both resultsmust be clear.

The explanation of these differ-ences can be shown by meansof a map that plots these devia-tions as they occur in space.The map also shows the reliefand the data set used.

The relation between the dataset used and the results obtainedmust be very clear now. Thelargest deviations occur precisely between the meshes of the data net. It is also remarkable that they occur atthe edges of the area and are successively positive and negative.

The next step in our research concerns the influence of the point density in the pattern. We have chosen toperform the calculations on the pattern that consists of both directions and with the smallest distance betweenthe track. The results obtained with 100%, 50%, 25%, 10%, 5% and 1% of the total data set are shown in thenext graph.

The use of even 5% of the available data doesn’t result in a performance decrease of the model. However whenwe make use of only 1% of the data, the model becomes unstable. The big advantage of low percentages ofdata expresses itself in shorter calculation times.

Figure 3. r-correlation all patterns.

Figure 4. Influence test set.


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Figure 5. Deviations map - lt4.

Figure 6. Influence of point density on track.


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Conclusion.

About the use of the model we have made the following conclusions. Fistwe will consider the model for a direct mapping. The most importantfactor is then the accuracy of the mapping that can be achieved with themodel.

For the model based on the total data set and with the settings : m = 10, n= 10, L

1 = 3500 and L

2 = 3000, the results can be found in the preceding

table. Important are of course the extreme deviations, which are in thiscase -1.80 m and 1.35 m. In spite of the very high correlation r = 0.9972,these deviations are not to tolerate, and we are interested were these de-viations occur. Therefore we mapped these deviations together with therelief, as can be seen in the following figure.

This map shows that there is an explanation for the larger deviations. They are as it happens related to therelief, and more particularly with the occurrence of sandwaves on the sand bank. With the exception of thesestructures (the sandwaves) the model is capable to restrict the deviations to the interval [-0.20, +0.20]. Fromwhich we must conclude that the model is able to map the general structure of the bank, but not the smallerstructures that occur on the sandbank.

This leads us to a next step, were we see the model as a tool for a further and more accurate mapping by meansof local interpolation methods like kriging.

Table 1. Parameters model 10x10 lt1.

Mean D 0.20Variance D 0.36

Min D -1.80Max D 1.35MAE 0.3328

RMSE 0.4161RMSEs 0.2039RMSEu 0.3627

a 0.1611b 0.9973r 0.9972d 0.9982


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Figure 7. Deviations map - lt1.

References.

Bracewell, R. (1965) The Fourier Transform and Its Applications. McGraw-Hill.

Davis, J. (1986) Statistics and data analysis in geology. J. Wiley, New York.

Hwei P. Hsu. (1967) Fourier Analysis. Simon and Schuster, New York.

Kreyszig, E. (1988) Advanced engineering mathematics. John Wiley & Sons.

Tokstov, G. P. (1962) Fourier Series. Prentice-Hall, Englewood Cliffs, New Jersey.

Willmott, C. (1984) On the evaluation of model performance in physical geography. Spatial statistics and models. D.Reidel publishing company, p443-460.


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Session / Séance C6-C

Making practical and effective electronic aeronautical charts

Sonia RivestDMR Consulting Group [email protected]

Rupert BrooksCanada Centre for Remote Sensing, Geomatics [email protected]

Bob JohnsonAeronautical and Technical Services, Geomatics [email protected]

Abstract

In order to take advantage of the opportunities presented by new display technologies, Aeronautical and TechnicalServices (ATS) was involved in research to determine the best way to reproduce and distribute digital chartswhich are based on the current paper charts produced by ATS.

These charts had to be designed to meet many difficult constraints, while still maintaining the overall goals ofclarity, accuracy and aesthetics. Safety and integrity of data is a major concern when producing aeronauticalcharts. Not only does the electronic version have to contain all the same information as the paper chart, itmust also be easily perceived by the end user to be of the same quality and authority as the paper version. Thebest way to accomplish this is to make the electronic chart look as much as possible like the paper chart. Theresulting charts had to be transferable across a network or by CDRom media with only minor modifications,and be compatible with all major computing platforms. At the same time, software and hardware costs neededto be kept to a minimum, particularly for the client viewing the chart. Finally, the disruption to the existingpaper chart production environment needed to be minimised.

Many different software packages can be used to produce charts to be visualised on a screen. The choice isbased on many criteria like the users’ needs and the existing chart production process. At Aeronautical andTechnical Services, Adobe’s portable document format (PDF) was chosen and a combination of software wasused to transform the digital files used for the paper chart production to PDF digital files. The transformationprocess was designed in order to fulfil all the requirements described previously. The process ensures aconsistency between the paper and the electronic charts because they are produced from the same digital files.

In addition to overcoming the cartographic challenges of a screen medium as opposed to a paper medium, thenew electronic charting technology can enhance the capabilities of a chart. Elements on charts were linked toother charts, publications and databases, using the interactive capabilities of the PDF. This interactivitygreatly enhances the usefulness of a chart, by placing more information at the user’s fingertips more quickly.Creating a system to provide this information reliably in the face of frequent changes requires a fundamentalunderstanding of the technology behind the scenes.

This paper will describe the work that is ongoing in the Aeronautical Charting group in this area, and willdiscuss the achievements to date. How a screen medium differs from a paper medium, how the electronicaeronautical charts have been designed and how digital charts can exploit their connections to the databaseboth on and off the Internet will be discussed.


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Introduction

In 1997, Aeronautical and Technical Services (ATS) began actively researching and developing technology forelectronic distribution of aeronautical charts. ATS produces many different types of aeronautical charts anddocuments but the research focused on the Enroute charts, the Canada Flight Supplement (CFS) and the CanadaAir Pilot (CAP) which are actually being produced digitally.

The Enroute charts are used for instrument flying. They cover large areas, and show little to no topographicbase information, but show copious amounts of airspace, navigational aid beacon and airport information. TheCFS is a handbook describing all the airfields in Canada, with the information that a pilot might need. TheCAP describes approaches to each airport. There are corresponding military publications for each of these thatdiffer slightly in form and contain a bit more information. All information was put online in this project, butwe will continue to refer to these publications by their common, civilian names. This paper first presents thefundamental differences between paper and digital charts. The second section explains the specific require-ments that the new digital documents would need to fulfil. Then, details about the technology available duringthe research are given. The final section presents the process developed and implemented at ATS.

Screen vs. Paper: What is the digital medium?

Like many other aspects of communication, the art and science of cartography has been revolutionised by theuse of computers. Maps are not only produced and analysed on computers, but they are increasingly beingviewed on computers, and it is not uncommon for a map product to be heavily used yet never put on paper. Itis clear that the production of a map for computer use is not as simple as just displaying a picture of the papermap on a computer screen, but how it should be done is still not well understood [Petersen, 1995].

This change in the medium of expression has led inevitably to a change in the methods of using the map[McLuhan, 1964]. Despite this change, the ultimate purpose of cartography remains unchanged. The intent isstill to communicate information about a spatially defined set of information to the map user. Furthermore,maps have traditionally been documents to be studied intensely with the user learning more the longer theyspend examining it. This type of use is still valid, although the way the user interacts with a map has changedgreatly from the paper to the screen. Because of differences in the capabilities and methods of using a map onthe screen, there are differences in the effective cartographic techniques for each medium.

The screen-based map has forgone the high resolution of paper, but has gained instead the potential ofinteractivity. Although computer screens are being improved all the time, their effective resolution is still onlya fraction of the detail that can be shown on a piece of paper. Furthermore, the average computer screen isbetween 15 and 21 inches on the diagonal, while paper maps are usually on the order of 2 to 3 times that size.Fortunately, the computer gives the capability of zooming in, and changing the level of detail if necessary. Theuser can also make queries of objects on the map, which changes greatly the need for labelling. The capabili-ties of zooming and querying change the whole process of cartography. Scale – once a defining characteristicof the paper map – has now become arbitrary, and a whole host of information that used to be implied by scale(such as accuracy) now must be made explicit. Furthermore, the requirements of generalisation have changed.In the paper map, generalisation was driven by the requirement of readability, printability and the desire tocreate an accurate summary. On the screen, generalisation is still related to readability, but in an entirelydifferent fashion. The printability criterion has been replaced by a need to conserve bandwidth. Nevertheless,the final criterion, which is to create an accurate summary, remains the same.

To add further difficulty to the cartographer’s task, it is often required to produce paper and digital versions ofeffectively the same map from the same source information. While the requirements of the end products are


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quite different, it is necessary to use the same processes wherever possible to minimise error, and to enhanceefficiency. Also while it might be ideal for technical reasons to completely change the appearance of the charton the screen from the one on the paper, this would not be practical for most users. The average user ofaeronautical charts has been trained on paper charts, and if the differences between paper and screen are tooradical, they will lose confidence in the chart, or worse still, be unable to interpret it quickly and correctly.

Requirements at ATS

When publishing to a digital medium, the potential seems limitless. However, there are a number of practicalissues that should guide any design. One of the most important is the clients intended use, and the machinesand software that they use. In the case under discussion, however, it was found that the possible client plat-forms were diverse. The intended platforms for use of digital aeronautical charts ranged from high-poweredUNIX workstations isolated from external networks, to Web-aware desktop PC’s. Furthermore, although itwas not explicitly part of the design, some thought was given to in-flight displays. ATS believed that whatevertechnology was chosen should not lock out that possibility. This range of target systems had a profoundinfluence on the technology chosen.

Secondly, ATS produces different types of aeronautical products designed for different users. Each productnecessitates a particular production process. Since 1994, the Enroute charts have been digitally produced on a56-day cycle basis, in accordance with the International Civil Aviation Organisation (ICAO) publication cycle.The effective date of a chart is fixed and the deadline cannot be moved. During the first 28 days of every cycle,changes in the aeronautical information, provided by Transport Canada, NAV Canada and the Department ofNational Defence, are validated and included in the Canadian Aeronautical Charting (CANAC) database. Thechanges are then extracted and symbolised in digital vector files using a suite of software designed exclusivelyfor aeronautical charting. A manual cleaning is done on every vector file in order to integrate the changes tothe previous version of the chart. Only the changes are extracted from cycle to cycle in order to reduce thecleaning operation. The aeronautical charting software then combines the vector files and transforms them toraster files to produce the negatives. Once these are printed, the paper charts are finally ready to be distributed.The CAP and CFS are also revised and published every 56 days. Because the time requirements for theproduction of the paper documents (charts and books) are very tight, the new digital document productionprocess would have to be integrated with the existing process as much as possible. This would help minimisethe production costs and would require minimal extra effort from the product specialists. Also, in order tomake sure that the digital documents contain the same information as the paper documents, both would have tobe produced from the same source of information. This is a very important safety factor.

As in any project, cost was an important requirement. There are three main sources of cost in digital publica-tion. These are the production of the data and software, licensing fees, and support costs. As the data wasalready being produced, the costs were managed by integrating the digital production as tightly as possible tothe existing paper process. A COTS (Commercial Off The Shelf) software solution was preferred for cost-effectiveness and speed of implementation. When licensing software products for publishing, there are twomajor ways of applying the costs. One method requires a large outlay for software that will be used to producethe media, but special viewing software, if needed at all, is free. Thus there is no per user seat licensing costwith such a system. Because ATS expected a large client base, this type of solution was considered the mostappropriate. Alternatively, there are systems with lower up front cost, but which require a license fee or royaltyto be paid for each user who ends up using the client software. Clearly, as the number of users increases, thisbecomes a less appropriate option. Finally, the support costs may be extremely difficult to quantify. Thesemay include opportunity costs of lost business due to product failure.


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Also, the design of the new digital documents would have to take into account the need for clarity. This couldbe implemented by using a level of detail appropriate for the zoom level. On a computer screen, it is notpossible to show everything that is on the paper chart at the same time, so it is important to allow the users tochoose the information they need or want to see. It is also important that the users feel comfortable with thenew charts. These should then have the same or similar colours and symbols as the paper documents.

Finally, the digital aeronautical document production process would have to be adaptable to other ATS prod-ucts like the Air Traffic Control (ATC) charts. These ATC charts are produced on demand and contain a subsetof the elements found on the Enroute charts.

Investigation of Available Technology

The World Wide Web (WWW) has shown tremendous success in the realm of electronically distributing infor-mation. It has grown astronomically in the short time since its development. Working under the assumptionthat the WWW must be doing something right, ATS had decided to investigate “web-enabled” technologies foruse in publishing these digital products. As research progressed, it became apparent that there were a numberof related technologies involved in the web’s success, and they shared several attributes that contributed to theweb’s effectiveness. By understanding and harnessing those attributes, ATS has been able to develop a veryflexible and expandable process for publishing electronic aeronautical charts.

In common usage, the term “the web” refers to a vague collection of technologies. Some of these technologiesare protocols, some are languages, some data formats, and some are proprietary software. There were twoimportant and independent aspects of these technologies that related to the core of the problem of producingdigital aeronautical documents. One was the use of open, widely understood data formats, and the other wasthe use of client-server computing. Both of these concepts are well tested in practice, and ATS has woventhese ideas into the core of the digital chart design.

Open, Widely Understood Data Formats

There are a number of data formats, for different types of data, which are closely associated with the Web.Examples include hypertext markup language (HTML) [Raggett et al., 1998], joint photographic experts groupimage format (JPEG) [CCITT, 1992], and ECMAScript (better known as JavaScript or Jscript) [ECMA, 1997].These examples run the gamut from describing formats for rich text, to programming languages, but they sharea number of common attributes.

· Client-Side platform independence

Notwithstanding the efforts of many software companies, there are many different computer hardware sys-tems, operating systems, and viewing software. As mentioned, the potential clients for any digital electroniccharts would have a diverse number of different platforms. The exact details of how a programming orscripting language can be platform independent are beyond the scope of this paper. In general, it is accom-plished through the use of an abstract virtual machine to isolate the programming environment from thediverse hardware on which it may exist. More detail may be found in McComb et al. [1997] and ECMA[1997]. The popularity of these formats is attributable to the availability of software to work on them on anyplatform.

· Open standards

The standards for each of these formats is publicly available to any interested party, and may be freely usedwithout patent or copyright infringement. In part, this enables client-side platform independence, becauseany company or individual can create or adapt software to work with these formats. Furthermore, the open-


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ness of the standard allows experts to evaluate and comment on the technical details, which can reveal flaws,or provide insight.

· Inexpensive viewing software

The openness of the standards involved encourages the proliferation of software to deal with information inthat format. In each case, either through competition, or the explicit creation by promoters of the format,tools to view and work with the format are widely available.

· Wide usage

Partly because of the client-side platform independence, but mainly because of the availability of inexpen-sive software, these formats are in wide use. This wide use means that the overhead of maintaining theviewing software becomes very low, because of familiarity, and because of its use for many purposes.

Aeronautical charts contain symbolised geographic objects, which are described in a very abstract way. Theseare ideally represented as a vector GIS dataset. To date, however, the web formats do not include any vectorformat. This greatly limited the choice of formats available to ATS to use for digital aeronautical charts. In allcases, some software that was not, strictly speaking, a web standard, would have to be used. Any format mustbe supported on the machine used to view it by some software. It was certainly not reasonable to ask all ATSclients to support an entire GIS system just to view digital aeronautical charts. Therefore some vector formatwhich met the criteria listed above was required to allow keeping all the advantages of the client-server com-puting involved in the web, while using the advantages of the format.

There has been much excitement about using plugin components that understand GIS type data to view spatialdatasets in a web browser environment. Because of ATS requirement for extremely fast production time, thisapproach showed great promise. The transformation from the GIS data formats used internally in ATS werenot too severe, and were easily automated. In fact, the Intergraph GeoMedia Web Map Version 1 plugin systemwas used during the first phase of the project. However, none of the plugin systems available from the majorGIS / drafting vendors has cross-platform support at this time and all have only limited graphics flexibility[Limp, 1997]. (Note that Autodesk has very recently added Java-based cross-platform compatibility to theirsystem.) This severely weakened the viability of this approach for ATS, as the client base was known to use awide variety of machines and operating systems. There are XML based vector graphic being developed cur-rently, which show great promise, but are not yet ready for implementation. There was only the Adobe PDFformat available which possessed the attributes considered necessary to produce an effective product.

Portable Document Format (PDF)

The Portable Document Format (PDF) was developed by Adobe Systems Inc. to provide a means of displayinggraphically rich, page-based information. Although originally not intended to support maps, the paradigmused by PDF easily adapted to this use. PDF is a page description language which uses a subset of the Post-script drawing engine to produce graphical representations on screen which maintain the layout, colour andgraphic design of the original document [Adobe Systems Inc., 1997]. The format is open for public review,and the viewing software is free, and available on a wide variety of platforms. Due to its use of the PostScriptdrawing model, PDF presents very high quality graphics and text and is very flexible on the colours and fontsside. It is a hybrid raster - vector format, and its support of vector information allowed for effective productionof small files. Every single element of the document is described separately in the file so it is possible tomanipulate it, for example to create customised links. Finally, the format supports the description of http basedhyperlinking, and the use of ECMAScript / JavaScript to provide custom interactivity. This means that the useof this format does not in anyway preclude the use of client-server computing or possible future development.


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Client-Server Computing

The client-server model of computing involves the division of computing processes into client and serverprocesses. Server processes listen for and respond to requests from the client processes. A client and a serverprocess may reside on the same machine, or on greatly separated machines connected by a network [Taylor,1997]. The use of client-server processing by the WWW involves the use of the HTTP protocol to requestservice from servers that may be widely separated from the client processes [McComb et al, 1997]. This iscompletely independent of the use of the data formats described in the preceding section. The HTTP protocolcan be used to distribute any type of data, and there is no requirement to use a standard web port (80) or to usea web browser to make requests [Fielding et al, 1997].

The primary advantage of client server computing is that it allows an author to create a division of labourbetween client machines, which can be extremely diverse, and server machines, which the author may havefull control of. The alternative is to have all required software running on and developed for, the end user’smachine. When the end user may be using any one of a diverse variety of platforms, developing customsoftware to run on all of them becomes a tremendous chore. Nevertheless there are advantages and disadvan-tages to both methods.

Having all the software located on the end users machine has two major advantages. The resulting productwill be self-contained, and independent of any network connections. Furthermore, once the product is pro-duced it requires no further effort. It can be stored and distributed on a fixed medium, and will continue towork even if the producer is not actively supporting the machines involved. The disadvantages of this method,however, can be severe. ATS was in a situation where the potential users operated a wide variety of systems,and developing custom software for all of these systems would have been prohibitively expensive. This meantthat for this solution to work, all the desired functionality would have to be available in a COTS solution.

Using a client-server approach provides the major advantage that most or all custom programming can be doneon the server side of the system. This means that the programs can be written for a very specific machine, or setof machines, which the developer has access to and control over. Furthermore, it may be easier to restrictaccess to the server to authorised users. However, the convenience of this server has a price. It is up to thepublisher to maintain it, and keep it running and up to date.

Clearly, using a server only becomes an advantage when custom programming is required. Custom program-ming will be required when the author desires functions from the published product which are not explicitlyavailable in viewers for the format, and cannot be precalculated and prepared in advance. For example, webbrowsers support the viewing of images, but do not support zooming. For an author to support zooming into animage in this environment, they must either have a program that will do the zooming, or they must pregenerateall possible zoom levels, and generate the links to them within the data.

Some types of interactivity, therefore, require custom programming and can add greatly to the cost and diffi-culty of a project. When planning interactivity in a digital publication, it is critical to differentiate betweeninteractivity that is implied by the medium, and is therefore packaged for free with existing software viewers,and interactivity that must be programmed by the author. The differences are subtle, because some of theformats being discussed are actually programming languages that may have a great deal of functionality. Thekey to making this differentiation lies in the level of abstraction of the language, and how successfully platformdetails have been hidden from it.

Viewing, zooming and panning and linking is available with the software for any of the formats that ATS wasconsidering. The capability of querying was the area where issues of customisation came to the forefront.There are two approaches to querying. In one, all query results are precalculated and treated as links. This typeof interactivity is still quite simple to implement. However, it requires the author to imagine all possible userqueries in advance, which may not be possible. Even when all possible queries can be accurately imagined, the


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implementation of such a plan may be impossible because the number of possible queries (and therefore an-swers which must be precomputed) may quickly become astronomical. The other approach is to be able tospecify a query that requires processed at run-time. This query could be either spatial or non-spatial in nature.For this type of interactivity some programming must be done. The processing can be done either at the clientend or the server end or with some combination thereof. On the whole, the choice of whether or not to use aclient-server approach depends on what types of queries would be supported, and to what degree the responsesto them can be precalculated.

Experimentation, Development and Implementation

ATS possesses a large database of information about airports and other objects on the aeronautical charts. Inaddition, two publications, the CFS and the CAP encapsulate the information about airports in a book format.ATS was able to experiment with both a database query approach, and a pregenerated approach..

In the database query approach, the database was loaded onto a machine with an http server, and CommonGateway Interface (CGI) programs were used to provide a query service. By passing the name of an airport,for instance, to the CGI process, the database would be queried, and relevant information formatted and re-turned. The advantages of this approach were that it was low in cost, as the database was already beingmaintained, and it was quick and effective. When using a plugin based approach, the links to the database keywere already present because the geographic data was already linked to the database.

It was also possible to use the precalculated approach because of the existence of the CAP and CFS publica-tions. The individual pages of the CAP and CFS books were already prepared in postscript format for thepress. It was a simple matter to convert these to PDF format for online viewing. As the CAP/CFS pages werealready identified by airport, it was fairly simple to establish the link to them from the database. As the data-base was associated with the plugin-based chart, this provided a nice binding between the different productsand information available, and placed all information that a user might desire within one or two mouse clicks.In the beginning of the research, a plugin approach was used, and this required a server process to be runningcontinually. This prevented the precalculated queries from reaching their full effectiveness at this stage.

The plugin approach, however, was seriously flawed by its lack of graphic flexibility, its platform dependence,and its requirement for a server process even for precalculated responses. For that reason, ATS chose to lookat the PDF option for publishing digital charts. This option resolved both the platform dependence and carto-graphic appearance issues, but as a visual representation was no longer directly linked to the database. It wasnecessary to re-establish the link between the chart, and the database.

In the beginning, this appeared to be a technical headache to overcome, but it allowed even further flexibilityin the long run. It is possible to define a link within the local filesystem in the PDF file, and this enabled thesystem to be free of its network dependence for those queries that had precalculated answers. Because the PDFformat supported HTTP based hyperlinking, using PDF did not rule out using client-server based queries. Asthe necessary information to create these links was completely represented in the database already, it was onlynecessary to generate the link information for each chart, and to insert that link into the PDF file.

Based on this choice, an appropriate process had to be designed to transform the three types of documentsunder study into the PDF format. The actual paper document production processes used at ATS facilitated thedevelopment of the new process. For the Enroute charts, the software that actually produces the digital vectorfiles during the extraction and symbolisation has the capability of plotting files in postscript. Having docu-ments in this format, it is very simple to produce the corresponding PDF files. Also, the CAP and CFS are bothproduced directly in the postscript format.


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Figure 1: Web browser interface

The final prototype system that has been developed allows PDF charts to be linked as stand-alone documents,or to be viewed through a web browser interface. The web browser interface also allows the use of the IntergraphGeomedia Web Map plugin for viewing data. Many queries can be handled in a precalculated way, but iffurther sophistication is required, there is no reason why a server cannot be used. The web browser interface isshown in Figure 1.

Digital Enroute Charts production process

In order to minimise the duplication of efforts, the transformation process starts with the cleaned vector files.A copy of these files is transferred to the digital charts production process while the original paper chartproduction process remains unchanged. The cleaned files are then customised prior to the postscript plotting.This customisation step is necessary because the colours and symbols originally used for the paper chartsproduction process need to be changed to reflect the printed paper charts. The postscript files are then pro-duced, transformed into PDF files and an application is run to generate the links to the database. The resultingPDF files can also be linked together and to other digital publications. This digital Enroute charts productionprocess can be completely automated and can be adapted to produce the new digital CAP and CFS as well.Figure 2 shows the integration of the digital charts production process within the paper charts productionprocess. The two processes can work in parallel.

Design details

The design of the visual representation of the new digital Enroute charts addresses many aspects. The mainones are the colours and the levels of details. The choice of colours was primarily based on the colour stand-ards actually used for the paper charts. Each colour has a particular signification and it was important to keepthis association when designing the new digital charts, so these are easy to read by current paper charts users.On the paper charts, aeronautical information is coded in shades of green and grey. The same colours have


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been used on the digital charts. The important symbols like the airports and navigational aids have been madebrighter so they are easily distinguishable from the background [Kaufmann, 1987]. Also, a light backgroundhas been used as it facilitates the colour perception of symbols [Eaton, 1993]. In order to make the chartclearer, three levels of details have been defined. The first one contains only the features needed to locate thearea of interest. The second level adds the aeronautical information symbols and the last one includes all thetext. Figure 3 shows an example of PDF chart.

Figure 2. Actual Enroute charts production process

Figure 3. Sample of an Enroute paper chart (left) and of an Enroute digital chart (right)


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Conclusion

After investigation and experimentation, the PDF format appeared to fulfil all the requirements of the Aero-nautical and Technical Services for the online publication of aeronautical information. The PDF format isplatform independent, it allows high quality graphics and text as it is derived from the postscript and the vieweris free. This format has the ability to contain links and because of its support of the JavaScript / ECMAScriptlanguage, it allows the creation of customised interactive functions.

The process developed at ATS integrates into the existing paper document production process. The digitaldocuments are produced from the same digital files as the paper products, so they contain the same informa-tion. This guarantees the integrity and consistency of the aeronautical information. This process is flexibleand can be adaptable to other charts and publications that ATS produces with minor modifications. A proto-type system has been developed that allows the charts and publications to be linked together as a stand-aloneproduct with some query capability, or to be integrated into a web browser environment using server processesto do more sophisticated queries.

References

Adobe Systems Inc. (1990). Postscript Languages Reference Manual 2nd Edition. Addison Wesley.

Adobe Systems Inc. (1997). Portable Document Format Reference Manual, Version 1.2. Available from www.adobe.com.

CCITT, (1992). Information Technology – Digital Compression And Coding Of Continuous-Tone Still Images – Re-quirements And Guidelines. CCITT (the International Telegraph and Telephone Consultative Committee)recomendation T.81. Also known as ISO/IEC International Standard 10918-1. Commonly known as JPEGimage format specification.

Eaton, R.M. (1993). Designing the electronic chart display. The Cartographic Journal, 30, 184-187.

ECMA, (1997). ECMAScript Language Specification. ECMA - European association for standardizing information andcommunication systems. http://www.ecma.ch

Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Berners-Lee, T. (1997). RFC2068 Hypertext Transfer Protocol — HTTP/1.1. http://www.cis.ohio-state.edu/htbin/rfc/rfc2068.html.

Kaufmann, R. (1987). Colour considerations for electronic charts. Technical Memorandum, Department of NationalDefense, Canada.

Limp, W. F. (1997). Weave Maps Across the Web. GIS World. September, 1997 pp. 46-55.

McComb, G., Bower, M., Robinson, M. (1997). Web Programming Languages Sourcebook. John Wiley & Sons.

McLuhan, M. (1964). Understanding Media: The extensions of man. McGraw-Hill, Toronto.

Netscape, Inc. (1997). Netscape DevEdge Library Documentation. http://developer.netscape.com/library/documenta-tion/index.html

Peterson, Michael P. (1995). Interactive and animated cartography. Prentice Hall, Englewood Cliffs, N.J. ; Toronto

Raggett, D., Le Hors, A., Jacobs, I. (Eds.)(1998). HTML 4.0 Specification. World Wide Web Consortium recommenda-tion. http://www.w3.org/TR/REC-html40/

Taylor, L. (1997). Client / Server Frequently Asked Questions. http://www.abs.net/~lloyd/csfaq.txt


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Session / Séance 06-D

Environmental Mapping of Russia’s Seas Using GIS

I. Suetova and L. UshakovaDept. of Cartography and Geoinformatics,Faculty of Geography, Moscow State University,Vorob’evy Gory, Moscow, 119899 RussiaPhone: 7(095) 939 37 93 Fax: 7(095) 932 88 36E-mail: [email protected]

Preface

The intensive anthropogenic impact on Russia’s inland and adjacent seas in the process of utilization of theirresources in recent decades resulted in the pollution of some of their areas, disturbance of the entire complex ofnatural conditions, and decrease in the natural ability of sea ecosystems for autopurification.

The information system for observation and analysis of the state of natural environment, first of all, of thepollution and its effect in the biosphere, brought the investigation of natural phenomena to a new level. Thestudy of the ecological results of the human economic activities at the seas takes two forms. One of these is thegeochemical monitoring of sea environment, which involves the monitoring of abiotic factors including thehydrographic ones such as the temperature, salinity and pH value of sea water, the biogenic elements such asoxygen, nitrogen, phosphates and silica, and the monitoring of the factors of anthropogenic impact such as thespreading of chlorinated hydrocarbons, pesticides, petroleum hydrocarbons, heavy metals. The other form isthe biological monitoring of sea environment, i.e., the analysis of the behavior of sea ecosystems under theseconditions.

The inadequate amounts of available information add to the importance of monitoring and of the accumulateddata base from the standpoint of analysis of both the natural processes, such as the seasonal and annual changesin sea ecosystems and hydrodynamic and climatic variations, and the anthropogenic impact on the sea surfaceslocated in different latitudes.

Because the local pollution and its negative results at the seas may have a large-scale and even global effect,GIS mapping of the seas, which enables one to take into account the natural relationship between elements ofsea ecosystems and the dynamics of natural phenomena, assumes special importance in developing the systemof integrated ecological monitoring.

Mapping of the Active Sea Zones

The results of numerous investigations of recent years demonstrate that the sea pollutants come from atmos-pheric precipitation and river and terrigenous runoffs. Along with large masses of industrial and sanitary sew-age that flow to the sea year after year without any purification, major sources of pollution include irrigationsystems, agricultural washoff, coastal and offshore oil and gas fields, water engineering, and emergency dump-ing of oil from tankers and pipelines.

The seas are polluted the year round with harmful pollutants such as oil, phenols, detergents, heavy metals,biogenic elements.


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The pollutants are distributed nonuniformly in the seas and form high-level zones in the top euphotic layer, inlittoral areas, and in the regions of convergence of water masses, that is, in the ecologically important seabiotopes in which the bulk of biological products are created.

In mapping inland and adjacent seas, special attention should be given to the active zones, i.e., places of higherintensity of geographic processes, in view of the fact that the intensity of the processes corresponds to theintensity of transformation of matter and energy.

The zones of higher transformation of matter and energy as a result of hydrodynamic, physical, chemical, andbiological processes usually emerge at places of intersection of several boundary surfaces. These are coastalzones such as the ice edge (Arctic seas) or frontal zones such as places where water masses of different originsand different characteristics meet. The regions of development of the most active hydrodynamic and thermo-dynamic processes in the atmosphere and on the see surface include submerged springs, volcanoes and wells,river mouths, canyons, straits. They serve as channels for intensive exchange of matter between the sea anddeep-lying layers of lithosphere (for example, emergency dumping of oil in the Caspian Sea may cause localecological shocks).

River mouths are places in which slow global cycles of matter accelerate and the concentration of matteroccurs, and where the role of industrial waste is rather important. The estuaries and coastal sea waters are themost fertile places in the world. In the canyons, matter is transported from the coastal surface zone to the deepsea regions. The dynamics of the coastal zone, the shore destruction or accretion, the migration of river mouths,the balance of pollutants depend in places on the magnitude of this runoff. Straits and submerged rapids are ofunique importance to the circulation of sea water, redistribution of heat, slats and dissolved gases.

Description of Environmental and Anthropogenic Factors

The following environmental and anthropogenic factors have been treated in mapping Russia’s seas.

- The main oceanographic features: the temperature, salinity, and density of water of the surface sea layers, aswell as dissolved oxygen that plays an important part in the distribution of biomass and primary productivityof the seas being explored.

- The oceanologic conditions such as sea currents, circulation of water, hydrofronts of the upwelling zone.The pollutants coming to the shelf are redistributed there and then carried out to the sea. The sea circulationand hydrofronts of the upwelling zone play an important part in the transfer of pollutants.

- The biogenic elements that form the basis of mineral nutrition of algae in the process of photosynthesis.These are phosphates, total phosphorus, nitrogen (nitrite, ammonia, total), and silicon.

- The coastal processes responsible for the delivery of material to the littoral areas; special attention is given toshoal, where secondary pollution takes place as a result of the wave and wind activities.

- The bottom sediments form the zone of special critical intensity, in which the coefficients of accumulation ofpollutants are much higher than their concentration in surrounding water. Most of pollutants, such as heavymetals, molecularly stable chemical compounds, are sorted in the mass of water on settling particles, passthrough this mass, accumulate in the bottom sediments and in benthos.

- Atmospheric circulation, especially, on the land-sea boundary. The contribution by atmospheric pollutants tothe overall balance of anthropogenic pollution of the sea environment is compared at present with riverdischarge. Higher concentrations of pollutants, involved in biological cycles, have been discovered in sur-face water and, especially, in the surface microplankton.

- The biological sea and coastal resources as a measure of stability of sea ecosystems. The correlation betweenthe ecosystem biomass and primary productivity is calculated by the actual data on a unified scale for landand sea. The ecosystems of the coastal zone are most productive.


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The most significant anthropogenic factors are as follows:

- The industry, especially, that related to mineral resources (oil, gas, coal, uranium ore in the coastal zone andon the shelf) and transport in the coastal zone, its types and load capacity. The industrial centers are classifiedby the combination of branches of industry, degree of hazard, and the values of maximum permissible con-centration of air pollutants. The low, moderate, increased, high, and very high ecological levels of intensityare identified for industrial centers.

- The level of river pollution in mouth areas, defining the influx of pollutants to the seas, the overall volumesof their discharge, and the volumes of purified and polluted sewage.

- The level and sources of sewage pollution of the sea water surfaces proper.- The main sources of atmospheric pollution, their structure, volumes of emissions in the coastal zone.- Three levels of ecological hazard are identified for transportation centers and communications, namely,

moderate, high, and very high, with due regard for freight turnover and traffic, frequency of train movement,presence of polluting freight. Special attention is given to sea waterways, oil pipelines, bases of merchantand fishing fleet.

- Potential sources of pollutants such as objects that present the hazard of radioactive contamination of theenvironment, places of dumping and burial of solid and liquid radioactive waste at sea, bases of atomic fleet,nuclear reactors, and uranium mining and processing plants.

- Population density.

Investigation Methods and Results

The systems ecological analysis is usually based on a large body of data about the characteristics of the envi-ronment. The data storage is a necessary, but not sufficient, part of the project. The data must be readilyaccessible on request. The information from different sources must be correlated, compared, analyzed, andvisualized in the form of a table, scheme, map, or chart. The modern GIS technology provides the frameworkfor such studies and offers diverse possibilities for the acquisition, integration and analysis of spatial data.

Base layers of spatial information were automated using ARC/INFO. GIS ARC/INFO has a topological vectordata model. The topology creation is accompanied by the creation of the attribute table for each coverage. Theattribute table contains information about the type of the object, area and perimeter for polygons and lengthsfor linear objects, the internal and user identification number of the object. Such data model enables one toperform various spatial topological operations and correlate data of different types using location in space asthe common key.

Subsequent work (visualization, editing, combining and analyzing different layers of information, modeling,creating and editing legends and attribute tables, charts, layouts) was done in ArcView GIS 3.1.

A geographic map on the 1:10 000 000 scale was used as the base map when drawing the ecologo-geographicmap of the Arctic seas. This map was automated. ARC/INFO coverages included layers such as hydrography,sea shore, populated areas, latitude and longitude grid. The outlines of the polygon features, which representedthe basic thematic content of the map were likewise automated from separate paper maps. Such informationlayers on the topological vector data model of ARC/INFO represented sea areas with different stability of seaecosystems, sea shore stability, geomorphology of the sea shores, water quality of the streams, potential ofatmospheric pollution, location of wells and platforms on the shelf, areas of dumping of waste, industrial andmining centers. Linear coverages represented sea ice borders, ice openings, sea water circulation. Based onthese layers, a digital map composition of the ecologo-geographic map was compiled in ARC/INFO.

The Digital Chart of the World (DCW) was used as the base map for spatial location and modeling of distribu-tion of the point data about pollution of the Caspian Sea. This chart is a comprehensive, 1:1 000 000-scale,


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vector base map of the world, which consists of 17 geographic thematic layers, attribute and textual data thatmay be accessed, queried, displayed and modified using ARC/INFO software.

ArcView was used to create tables in DBF format, containing data on the concentration of different pollutantsin different years for different points of the sea areas, as well as the geographic coordinates of the samplingpoints. The use of the ArcView Spatial Analyst extension containing a wide range of new powerful tools formodeling and analysis of spatial data enabled us to calculate grid themes (georeferenced matrices of the distri-bution of different pollution parameters) from point themes. We used spline interpolation (with the tensionparameter) and IDW interpolation to compile maps of the distribution density of different pollutants in theCaspian Sea.

As a result, maps and diagrams of pollution by industrial sewage, oil, detergents, phenols, heavy metals, andpesticides were compiled, as well as maps of the dynamics of the water pollution index. The analysis of theresulting maps and diagrams for a ten-year period (1985-1996) revealed the dynamics and regularities ofdistribution of the sources and streams of pollutants in the sea.

At present, all of the results of ecologo-geographic mapping are in the ArcView GIS environment, whichmakes possible a multilayer map analysis. These maps are open for editing, union, and transformation into newmaps, as well as for operative updating.

The next important stage of environmental mapping is the estimation of negative ecological results of theanthropogenic impact on the sea environment. The results of anthropogenic influence on sea ecosystems mayshow up as changes in the average biomass of plankton and benthos, a simpler community structure and poorervariety of species, a larger number of indicator species of microorganisms, disappearance of the bottom fauna,reorganization of cenoses and appearance of species-installators, eutrophication and supereutrophication ofwater in coastal areas, gulfs, and bays.

The empirical scale of qualitative criteria of the ecological state of sea ecosystems includes four grades, namely,stable, transitional (from stable to critical), critical, and catastrophic.

In the process of ecologo-geographic mapping of Arctic seas and of the Caspian Sea (Dagestan coast), anattempt was made at assessing the state of sea ecosystems using the above-identified hydrochemical andhydrobiological indicators characterizing the sea environment and its ecosystems. The final estimate that char-acterizes the ecological intensity of the sea water surfaces being investigated involves the following indicators.

1. The water pollution index. There are five grades of the state of water, namely, relatively clear, moderatelypolluted, polluted, dirty, and extremely dirty.

2. The amount of basic pollutants in fractions of maximum permissible concentration for fishing. These in-clude petroleum products, phenols, detergents, heavy metals, pesticides, and biogenic products.

3. The oxygen regime.4. The changes in the average biomass of plankton and benthos.5. The simpler community structure and poorer variety of species.6. The growth of the number of indicator species of microorganisms.7. The disappearance of the bottom fauna.8. The reorganization of cenoses and appearance of species-installators.9. The eutrophication and supereutrophication of water, especially, in coastal areas, gulfs, and bays.

The integrated geographic analysis of the ecologo-geographic mapping reveals the ecological situation charac-terized by a rapid increase of concentration of pollutants in the coastal areas and by low concentration ofpollutants in the distant deep sea zones.

As regards the pollution level, the explored part of the Caspian Sea may be divided into three conventionalzones, namely, those of the most, medium, and least concentration of pollutants. The zone subjected to themaximum anthropogenic impact borders on the coast line and on the 10-meter isobathe on the outside.


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The hydrological regime of the Caspian Sea promotes the concentration of pollutants and their propagationwith sea currents along the coastal area. The zone of medium concentration (off-shore) is characterized by amore homogeneous composition of pollutants compared with the coastal area and is located between the 10-and 25-meter isobathes. The water surface zone between the 25-meter isobathe and open sea is characterizedby the minimum concentration of pollutants.

The analysis of the ecological situation of the Dagestan coast and Caspian Sea reveals that sea water in thecoastal area is polluted dangerously. Water in this area is characterized as “dirty” or “polluted” based on theintegrated estimation of the hydrochemical index of water quality. For the past ten years, the copper contentincreased eight times, that of zinc - ten times, lead - seven times, and of cadmium - five times. During the sameperiod, the content of mercury, petroleum hydrocarbons (up to seven times the maximum permissible concen-tration), and phenols (up to 13 times the maximum permissible concentration) increased as well.

The eutrophication of water, accompanied by plankton bloom and subsequent dying off, covers the entireCaspian coastal zone.

The most dangerous ecological situation is observed at the mouth and off-shore of River Terek. The amounts ofammonia nitrogen and copper pollutants coming from farming lands to the Terek mouth demonstrate that thisriver water cannot be used for fish breeding without preliminary purification.

Waste water from oil-processing and nonferrous metallurgy discharged from River Terek into the Caspian Sealed to the creation of zones of biological death in this area. The ecological situation deteriorated appreciably inthe regions of the towns of Makhachkala, Caspiisk, Derbent, and Izberbash, and at the mouths of Rivers Sulakand Samur. One can describe the ecological situation of the northern part of the Caspian Sea as a small distur-bance.

The ecologo-geographic mapping of Arctic seas made it possible to identify different classes of anthropogenicimpact on the water surface and coastal zones. The regions with the catastrophic state of ecosystems includethe Teribersk Inlet, the Barents Sea, the Bulunkan Gulf of Tiksi Bay in the Laptev Sea.

For the Dvina and Onega Gulfs in the White Sea and for the southern areas of the Ob’ and Tazovsk Inlets, thestate of ecosystems may be described as transitional from catastrophic to critical. The regions with the criticalstate of ecosystems include the water surfaces of the Kandalaksha and Mezen’ Gulfs in the White Sea, thecentral part of the Ob’ Inlet, Chaun Inlet, Pevek Channel, and the coastal zone of the Chukchee Sea.

The ecological situation of the water surface near the Novosibirsk Isles, west of Novaya Zemlya, in the north-ern parts of the Ob’ and Enisei Inlets, and in the central part of the White Sea may be described as transitionalfrom stable to critical. The situation of the water surface of the coastal areas and open sea in the East SiberianSea, and in the central part of the Chukchee, Laptev, Kara and Barents Seas may be described as favorable.

As a result of analysis of the geoecological map of Russia’s Far Eastern seas, the following may be regarded asecological risk regions: in the Sea of Okhotsk - the north-eastern shelf of Sakhalin, the Terpeniya, Aniva andTauiskaya Bays, and the water surface near the Oktyabr’skii settlement; in the Bering Sea - the Kamchatka andAvachinskii Gulfs and the Anadyr’ Lagoon; and in the Sea of Japan - the Gulf of Tatary and the inner part of thePeter the Great Bay.

Serious disturbances of the land ecological balance, which affected directly or indirectly the sea water surfaceconditions, were observed in the north-eastern and southern parts of Sakhalin, in the south of the Far-Easternregion, in the mining regions between the Amur and Khabarovsk Provinces, in the upper reaches of the Indigirkaand Kolyma rivers, in the vicinity of the towns of Petropavlovsk-Kamchatskii and Anadyr’.

The environmental mapping of Russia’s seas using GIS will help assess the results of human activities indifferent natural zones for subsequent ecological monitoring.


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Airborne remote sensing for water quality mappingon the coastal zone of Abruzzo (Italy)

Claudio ConeseI.A.T.A. – C.N.R., Via Caproni n. 8, 50145 Firenze (Italy)e-mail: [email protected]

Marco BenvenutiCe.S.I.A. – Accademia dei Georgofili, Via Caproni n. 8, 50145 Firenze (Italy)

Paola GrandeCe.S.I.A. – Accademia dei Georgofili, Via Caproni n. 8, 50145 Firenze (Italy)

The main goal of this work is to monitor the coastal environment of Abruzzo, a central Italy region, by meansof airborne remote sensing techniques. In particular the physical and biological dynamics of both natural andanthropogenic phenomena are pointed out. This work puts in evidence the importance of remote sensing inmapping and managing the territory and the environmental resources. Some processing methodologies definedto support the creation of a coastal monitoring service will be shown. The IATA and the CeSIA institutesdeveloped algorithms and analysis procedures of airborne remote sensing data to provide methodologies formapping the sea water quality along the Abruzzo coast. The airborne multispectral scanner, VIRS 200 (VisibleInfraRed Scanner), was used to collect images on different sites of the coast near the principal rivers foci inorder to monitor the presence and the distribution of water pollutants. The airborne system acquires in thevisible and near-infrared bands (400-1000 nm) and the channels are properly set for marine applications. Aseries of sea truth campaigns was carried out to collect the physical and bio-chemical parameters. For thispurpose the multiparametric probe IDROMAR IM51 was used. The measured parameters were correlatedwith synthetic indices, obtained from the remote sensed data, putting in evidence environmental phenomena.

Furthermore, the thermal camera ETS 512, detecting the thermal emission in the 8-12 mm band, was used inorder to create the thermal maps near some mouths of rivers. The temperature gradient between river-waterand sea-water allows to evaluate the distribution of the fresh-water into the sea.

Both VIRS 200 and ETS 512 was produced by Officine Galileo, Florence (Italy) and were available at theEnvironmental Control Centre of Atri (Italy). The two acquisition systems have spectral, radiometric andspatial characteristics useful for a detailed analysis of the environmental parameters.

Study area

The study area is located along the coast of Abruzzo, a central region of Italy, on the Adriatic sea, in proximityof the mouths of the following rivers: Alento, Pescara and Sangro.

The coast is characterised by the presence of breakwater, built during the last twenty years, in order to preventthe erosion phenomenon that reduces the width of the beach. This resolution has brought, as a consequence, tothe permanence of the water pollutants and the sediments, transported by the river to the sea, nearby the rivers


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mouths. The problem of water pollution can be studied by processingremote sensing images, acquired in the opportune spectral bands withthe desired spatial resolution. The remote sensing approach allows tocollect in a simple way information about different sites in severaldates, that can be related to the measured parameters providing a de-scription of the observed phenomenon (in this case the distribution ofwater pollutants). The environmental problem increases near the ports,where the pollution is due also to the maritime traffic. Pescara rivermouth is located near the port creating a channel extended up to thesea, and it is characterised by an offshore dam. This particular struc-ture of the port has produced a pollutants distribution with a typical“mushroom” shape.

The acquisition systems

The used airborne multispectral systemis the VIRS 200, designed and pro-duced by Officine Galileo of Florence(Italy) for environmental monitoring. Itis characterised by an high spatial andspectral resolution. The VIRS 200 is apassive system, able to detect andrecord the spectral radiance scatteredfrom the ground in the 400-1000 nmband of the electromagnetic spectrum.It is possible to program 20 channels,with a minimum band-width of 2.5 nm,among 240 possible channels, whosechoice depending on the specific appli-cation.

This system is a line scanner using a CCD (Charge-Coupled Device) matrix of 240 arrays of 512 pixels. Eacharray is sensible to a particular band. Only twenty arrays among the 240 available can be selected and, conse-quently, the resulting multispectral image has 20 bands. The image is digitised and recorded on a magnetic tapein a Band Interleaved Line format.

The spatial resolution of an airborne acquisition system depends on the flight altitude and is determined with

the relation: )2

arctg(*)(IFOV

hHl −=

where:

l: pixel dimension;

H: absolute altitude of the aeroplane;

h: elevation of the observed surface;

IFOV: Instantaneous Field Of View.

Thus, the flight altitude is established in function of the elevation of the observed area and of the requiredspatial resolution.

Figure 1. Geographic location ofAbruzzo

Figure 2. VIRS 200 system.


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The system consists of two principal components: the avionic section and the ground section. The avioniccomponent includes the detection unit, the acquisition and control unit and the data recorder, while the groundpart is the device used to read digital data and the software used to record the image on a computer in acompatible format.

Table 1. VIRS characteristics.

Spectral range 400-1000 nm Scanning PushbroomSpectral resolution 2.5 nm Pixels per line 512 pixelsSelectable spectral bands 20 over 240 Dynamic range 10 bitField of View (FOV) 37.6° Roll stabilisation 0.1 mrad rms (±15°)Instantaneous FOV (IFOV) 1.66 mrad Recorder data rate 1 Mbyte/sec

Table 2. VIRS spectral channels selection.

Channel λ0 (nm) Channel λ0 (nm) Channel λ0 (nm) Channel λ0 (nm)

1 448.75 6 521.25 11 641.25 16 801.252 451.25 7 531.25 12 661.25 17 831.253 461.25 8 558.75 13 681.25 18 858.754 483.75 9 578.75 14 721.25 19 901.255 501.25 10 601.25 15 771.25 20 961.25

The thermal camera ETS 512 (Environmental Thermal Surveyor) is a system for airborne remote sensing forenvironmental monitoring. The sensor acquires the thermal emission in the 8-12 mm band. The scanningformat adopted to create the image is the standard television one and the acquired images are recorded on avideotape. The IR images on the surveyed territory are partially overlapped because of aeroplane motion. Theflights are performed at constant altitude and are parallel and rectilinear. The infrared camera is located on theaeroplane in order to carry out a nadir view of the surveyed territory. The system is characterised by:

• high spatial resolution;

• high radiometric resolution;

• high field of view;

• thermal references of the instrument.

Table 3. ETS characteristics.

Spectral range 8-12 µmHoriz. Field of View (FOV) 38°Vert. Field of View (FOV) 28°Instantaneous FOV (IFOV) 1.5 mradPixels per line 512 pixelsPrecision < ±0.5 °CAccuracy < ±0.5 °C


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The two thermal references are provided by two thermoelectric elements based on the Peltier effect, for whicha junction of two different conductors (in this case drugged semiconductors), crossed by the current, producesan increase of the temperature in one side of the junction and a decrease of the temperature in the other side.The precision and the accuracy of the thermal references are better than ±0.5 °C.

The complete system is formed by the avionic subsystem and the ground subsystem. The first one includes thethermal camera, the control electronic unit, the remote control panel and the recording system. The groundsection, including the hardware necessary for the vision of the acquired images, allows to convert the signalfrom analogue to digital, to record the images line by line and to process them by means of a computingsystem.

Truth campaigns

The sea and rivers truth campaigns have taken place at the same time of the remote sensing campaign, becauseof the very rapid dynamics of the observed physical and bio-chemical parameters. The collected data werecompared to the multispectral data acquired by the VIRS 200 in the different selected bands and to syntheticindices, calculated by combining the spectral bands. The sampling points along the coast were chosen in orderto collect data in the nearby of the rivers mouths and along the coast considering how far from the foci the riverwater arrives but also taking into account the width of the swath observed by the sensor.

3.1 River campaign

The mouth river campaigns described in this paper took place in the following dates:

• 10.03.97: Vomano river (mouth survey);

Pescara river(mouth survey);

• 11.03.97: Sangro river (mouth survey).

The following methodology was applied for each river:

1. the multiparametric probe IDROMAR IM51 was used to monitor continuously for an hour the parameters:pH, temperature, dissolved oxygen (concentration and percentage), conductivity, turbidity, salinity;

2. acquisition of two samples for each measurement point and laboratory analysis of the typical chemical andphysical water parameters.

3.2 Sea campaign (14.03.97)

The coastal water campaign was conducted by using an equipped boat. Twenty sampling and measurementstations were determined and the surveys were carried out as follow:

· n. 2 transepts with sampling points at 150, 300, 1000 and 2000 m from the coastal line, in correspondence ofthe Saline and Pescara rivers;

• n. 2 transepts with sampling points at 150, 300 and 1000 m from the coastal line, in correspondence of S.Silvestro zone (Pescara sud) and Alento river (mouth);

• n. 3 transepts with sampling points at 150 and 300 m from the coastal line, in correspondence of Zanni zone(Pescara nord), Montesilvano sud and Silvi Marina zone.

The methodology used for the survey is:

1. the multiparametric probe IDROMAR IM51 was used, with a survey of a vertical profile on each station,on the following parameters:


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pH, temperature, dissolved oxygen (concentration and percentage), conductivity, turbidity, salinity, rela-tive density, chlorophyll “a” (through coupled fluorometer);

2. determination of 2 samples for each measure point (surface and floor) and laboratory analysis on someparameters.

The monitoring programme produced quite positive results although the sea conditions were not optimal. Dataacquisition was useful for the setting of the airborne equipment used during the remote sensing mission.

4. Methodology

The VIRS images of the Pescara port and the Alento mouth were acquired on 11.04.97. The platform altitudewas 3000 m and the consequent average ground resolution was about 3 m. A series of pre-processing tech-niques were applied in order to obtain corrected images useful for the subsequent processing. The consideredimages presented a strong periodical noise, called “striping”, more evident in the lower bands, in particular inthe blue band, more sensible to the absorption of the atmosphere. An algorithm, based on the FFT (Fast FourierTransform) is able to determine the particular frequencies (that in the frequency domain appear like straightlines) producing the striping. Afterwards these frequencies were eliminated by applying an Hanning filter andthan the IFFT (Inverse Fast Fourier Transform) was performed. The so obtained image is almost completelywithout striping noise and sharper. The georeferencing procedure belongs to the pre-processing techniques andallows to gives map coordinates to each point of the image. The used geographic reference projection is theUTM, ellipsoid International 1909, datum European 1950, zone 33. For the projection the orthophoto (ed.1982, Abruzzo Region), at scale 1:10000 was used in order to determine the Ground Control Points.

Principally two indices were calculated, the turbidity and the sediment concentration, making use of the spec-tral bands previously corrected. On the basis of the results of the spectral profiles analysis, it was possible tofind the correlation formulas defining the two indices:

)2(* 8710 ++= RLogbaturbidity

where a=12.729677, b=-46.020389, R87

=(B8-B7)/(B8+B7).

For the turbidity the bands 7 and 8 resulted more correlated to the sampling data. In Figure 3 and Figure 4 theturbidity maps for Pescara and Alento mouths are shown.

Figure 3. Turbidity - Pescara mouth. Figure 4. Turbidity - Alento mouth.


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The turbidity unit is the FTU (Formazine Turbidity Unit - ISO). Figure 5 shows the experimental relationshipbetween the turbidity samples, collected during the sea truth campaigns, and the coast distance. It is possibleto observe that there is a rapid decrease of the turbidity with an increase of the coast distance. Obviously thehighest values are reached near the river mouth or where the water is rather still (near the breakwater).

CoastDistance

Salinemouth

Pescaramouth

Alentomouth

150 58.43 46.985 9.655300 56.44 53.95 4.181000 6.97 25.11 6.0152000 5.24 13.14

Figure 5. Relation between measured Table 4. Turbidity values (in FTU) on the transepts.turbidity and coast distance for three rivers.

As concern the soil suspended index the experimental founded formula, using the band 1 and the band 8 of theVIRS image, is:

bBLnassi += )(* 18

where a=-0.0409, b=-0.7893, B18

=(B8-B1)/(B8+B1).

From the sediments concentration, measured during the river campaign, in sampling points located at differentdistance from the coast, a sediments index was extracted:

Figure 6. Suspended Solid Index (Alento river).


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The ETS 512 flied on march ’97, covering all the coast of Abruzzo. The flight altitude was 1000 m on sea level,with a swath of about 660 m and a spatial resolution of 1.5 m.

Figure 7. Thermal map (March ’93). Figure 8. Thermal map (March ’97).

Conclusions

The described activities were carried on to define a methodological approach able to provide regular andobjective information about the water quality parameters. In fact, the use of remote sensing techniques, vali-dated by the acquisition of truth data, can be useful to provide systematic and comparable information on alarge area. Thanks to the possibility of the VIRS instrument of setting the spectral position of the twentyacquisition channels, the system and the developed methodology can be tuned depending on the specific needs.The study shown how the combined use of a multispectral high resolution scanner and thermal camera canrepresent a very useful tool to monitor the coastal environment and, in particular, the water parameters. Aninteresting result of this research arise from the multitemporal comparison of the thermal images collected onthe Pescara. This analysis shown the different distribution of the freshwater into the sea before and after theoffshore dam in front of the port was built up (see Figure 7 and 8). This phenomenon is quite evident also in theresult of the multispectral image processing (Figure 3). From this analysis arise that the dams and the breakwa-ter placed along the coast to reduce the coastal erosion process, can be considered as one of main the causes ofthe increase of suspended solid concentration and water pollutants along some portions of the Abruzzo coast.

An important role is played by the truth campaigns necessary to collect the real parameters for the calibrationof the correlation models to be applied to the remote sensed images in order to have a spatialisation of therelated index and, consequently, a global view of the studied phenomena.

However, some problems came from the absence of an automatic georeferencing system on the used remotesensing equipment, problem that is much more heavy in marine environment where it can be very difficult tofind the reference points necessary for the registration of the acquired image on respect to a cartographicreference.


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References

Alberotanza, L., Masserotti, M.V., (1992). Fondamenti del telerilevamento ed applicazioni all’ambioente marino. AIT

Lillesand, T.M., Kiefer, R.W. (1994). Remote Sensing and Image Interpretation. John Wiley & Sons Inc., New York

Slater, P.N., (1980). Remote Sensing: Optics and Optical Systems. Addison-Wesley Publishing Co., Reading Massa-chusetts

Morel, A., Prieur, L. (1977). Analysis of variation in ocean color, Limnology and Oceanography.

Toselli, F., Bodechtel, J., (1992). Imaging spectroscopy: fundamentals and prospective applications. Klwer AcademicPublisher, London

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