tutorial: vector analysis operations - · pdf filepage 4 vector analysis operations topology...

Vector AnalysisOperations

with

TNTmips®

TutorialVECTOR

ANALYSIS

ORACLE

SPATIAL

DXF

MDB

Vector Analysis Operations

Before Getting StartedThis booklet introduces techniques used for common GIS tasks, such as updat-ing vector objects, generating buffer zones, dissolving boundaries between poly-gons with similar attributes, and using one vector as a cookie cutter for another.Through a series of exercises, it familiarizes you with the basic tools in thepowerful vector analysis processes that are part of TNTmips® from MicroImages,Inc. These tools are not available in TNTview® or TNTedit™.

Prerequisite Skills This booklet assumes you have completed the exercises inthe Displaying Geospatial Data and TNT Product Concepts tutorial booklets.Those exercises introduce essential skills and basic techniques that are not cov-ered again here. Please consult these booklets for any review you need.

Sample Data The exercises presented in this booklet use sample data distrib-uted with the TNT products. If you do not have access to a TNT products DVD,you can download the data from MicroImages’ web site. The first exercises inthis booklet use the VAO Project File in the VECTORAN directory of DATA. The objectsin the NE_DLG and EASTNGULFCOAST Project Files in this directory are also used as isare objects from some of the Project Files in the CB_DATA directory. There are alsoquery (*.qry) files that are needed for the exercises. Make a read-write copy ofall the sample data in the VECTORAN directory and CB_ELEV on your hard drive sochanges can be saved when you use these objects.

More Documentation This booklet is intended only as an introduction to thevector analysis functions in TNTmips. Consult the online materials atwww.microimages.com for more information.

TNTmips® Pro and TNTmips Free TNTmips (the Map and Image ProcessingSystem) comes in three versions: the professional version of TNTmips (TNTmipsPro), the low cost TNTmips Basic version, and the TNTmips Free version. Allversions run exactly the same code from the TNT products DVD. If you did notpurchase the professional version (which requires a software license key) orTNTmips Basic, then TNTmips operates in TNTmips Free mode. This bookletrefers to TNTmips, TNTedit, TNTmips Free, and TNTview as “TNT.”

You can print or read this booklet from MicroImages’ web site or from theversion you install. The web site is your source of the newest tutorial bookletson this and other topics. You can also download an installation guide, sampledata, and the latest version of TNTmips Free.

http://www.microimages.com

Merri P. Skrdla, Ph.D., 15 February 2012© MicroImages, Inc., 1999–2012


Vector Analysis OperationsA variety of TNTmips processes are involved intopological vector analysis. The processes consid-ered here include creating a subset of elements froman existing vector object, generating simple andmore complex buffer zones, polygon fitting toswarms of vector points, merging and combiningvector objects in a variety of ways, dissolving adja-cent polygons based on shared attributes, rastergeneration based on point density, and grid analy-sis operations.

These processes use georeference information toposition objects relative to one another. All appro-priate transformations are applied so that the ob-jects need not be in the same map projection. Ob-ject coordinates are used for positioning if none ofthe objects are georeferenced.

Typically in TNTmips, there is more than one wayto reach a result. You could, for example, get thesame results as the first exercise (Extracting VectorElements) by using the designated region to copythe same elements in TNT’s spatial Editor and past-ing them into a new vector object. You can get thesame results from the Vector Merge process as fromthe Add operation in Vector Combinations, but Vec-tor Combinations also provides the flexibility toselect a subset of the vector elements and / or lessthan the full object extents.

This booklet begins with an explanation of vectortopology types then moves to an exercise in whichyou use the Vector Extract process to extract partof a vector object for use in generating buffer zonesand subsequent vector combination operations.There are also exercises in Polygon Fitting and youare introduced to Point Density Rasters and GridAnalysis. These operations let you deal with a vari-ety of Geographic Information System (GIS) analy-sis and management issues.

STEPS

launch TNTmips

if not already installed,copy the sample datafiles for this booklet (seepage 2) to your harddrive

Vocabulary: Polygonalvector topology isrigorously maintained inTNTmips. Polygonaltopology requires that anypoint be in at most onepolygon and a node beplaced at each lineintersection (and at thebeginning and end of eachline). Other topologycomponents maintained byTNTmips include the linesthat originate from eachnode, polygon elements oneither side of a line, the lineelements that form eachpolygon, island polygonswithin a polygon, and theparent polygon for eachisland. Other topologytypes, which are describedon the following two pages,are also supported byTNTmips.


Topology TypesTNTmips offers three levels of vector topology:polygonal, planar, and network. Polygonal is thehighest, or strictest, level of topology. It requiresthat no two nodes have the same X and Y coordi-nates, all lines start and end in nodes, lines do notintersect other lines or themselves (nodes are in-serted where lines would otherwise cross), enclosedareas are defined as polygons, and any point can be

in at most one polygon. Polygonal to-pology is necessary if you want groundarea measurements, but it takes time andrigor to maintain, which may be unneces-sary depending on your application.

Planar topology requires that all lines start and endin nodes and no two lines cross, as with polygonaltopology. However, polygon information is notmaintained. With the exception of polygon fill-ing, planar and polygonal objects appear the same.Note the presence of nodes (red) at every positionwhere lines would otherwise cross as well as at thedangling ends, in the roads at the left.

Polygonal and planar objects can be 2Dor 3D; topology is maintained in the XYplane for these object types (polygonaldimensions and positions of nodes sepa-rating lines that would otherwise cross are

determined by projecting onto the XY plane).

Network topology places nodes at the start and endof all lines, but lines may cross themselves or otherlines. As with planar topology, there are no poly-gons. Note the absence of nodes where the linescross in the grid at the left. Although nodes neednot occur where lines cross, they can be present at

any intersection and are necessary for use innetwork analysis. The constraints imposedby 2D topology on 3D objects are eliminatedby network topology, which allows two nodesto have the same X and Y coordinates.

Polygonal Topology

File ManagerObject Properties

Planar Topology

Network Topology


Topology Applications and BehaviorMany classic GIS problems are related to defininggeographic areas, such as land ownership polygonsor protected site boundaries. Such applications re-quire rigorous polygonal topology. (Imagine theuproar if a point on the ground could fall into twodifferent ownership polygons.)

Planar topology may be appropriate for hydrologyif no lakes are present. Planar topology may also beappropriate for road systems that lack underpassesand overpasses (or other features that require net-work topology for proper representation).

Network topology is desirable for network analysistasks (routing and allocation) and other 3D projectsthat benefit from maintaining lines that representfeatures that do not intersect in the real world ascontinuous lines, such as an overpass / underpass

Polygonal,Planar, orNetwork Topology

Extract Insideand Clip

or

crossing.

Additional differences between object types be-come apparent when you perform vector opera-tions. In an extract operation, as at the right, pla-nar and network objects give similar results, but

Z

in a 3D combine operation, the results from polygo-nal and planar objects are more alike (see below).

Operator(over Source)

3D view of two polygonal, planar,or network objects; same as 3Dview of single merged networkobject.

Hydrology

Ground Water Surface

If polygons are present, poly-gons are main-

tained by the clippingboundary to retainattributes.

node Zvalues

interpolated

Merging 3D polygonal or planarobjects places nodes wherelines intersect when projectedonto the XY plane. The Z valuesare interpolated from those ofthe nearest vertices in the lines the node separates.

Below, the view at the near left has been tilted toward the viewer.

polygonalplanar ornetwork


STEPS

choose Geometric /Extract to / Vector fromthe main TNTmips menu

click on [Select] andchoose the HYDROLOGY

object from the VAO

Project File

set the Region optionmenu to Partially Insideand click on the Selectbutton to its right

click on the Regionicon in the ExtractionArea Definition Toolswindow, then click onthe Add icon inthe panel that dropsdown, and selectHYDROEXTRACTREG from theVAO Project File

click on the Includein Extraction Areaicon

click on [Accept] in theSelect Region window

click on [Run] in theExtract To Vector window

create a new file in thesame directory as thefiles you copied for thistutorial booklet

append the default objectname with EXTRCT andclick [OK]

Extracting Vector ElementsThere is a variety of methods for selecting vectorelements to extract. You can limit the elementtypes, use attributes or a query, or select elementsfrom the screen with the mouse or using a region.

You can also limit thearea to extract from.These methods can beused in combination aswell (for example, selectpoints by attribute andlines by query within aregion of interest youdefine).

Separate settings forlines and polygons let

you use the attributes of either or both for selectionand eliminate lines not part of polygons if desired.Polygons formed by selected lines are created whentopology is built for the extracted vector object ifthe input object had polygonal topology.

When you click on the Select button for the area toextract, two windows open (the Select Region andExtraction Area Definition Tools windows). Theinput vector is displayed in the Select Region win-dow. You use the tools in the Extraction Area Defi-nition Tools window to construct the boundary forextraction.

The Extraction Area Definition Tools window expands to includeRegion Manager functions when you click on the Region icon.

input vector input vector andselected region

extractedvector

turn all threeof theseoptions on


STEPS

choose Geometric /Compute / Buffer Zones

click on [Object] andselect the HYDROLOGY

EXTRCT object you made inthe previous exercise

on the Parameterstabbed panel set theTarget to Vector and theBuffer Type option menuto Multiple Equal, theStarting Distance to 100,the Ending Distance to500, and the Interval to100

check that the Save asSingle Object toggle is off

click on [Apply]

change the Target toCAD on the Parameterspanel and turn on theSave As Single Objecttoggle

click on [Apply]

click on [Yes] whenprompted to save, namea new file and pressenter, then click on [Auto-Name] and [OK]

click on [Save As] thencreate a new object inthe same file

keep this process openfor the next exercise

Generating Buffer ZonesThe Buffer Zone Generation process creates poly-gons at a specified setback distance from the ele-ments selected for buffering. You can select all or alimited number of element types for buffering. Youcan use attributes or a script or select elements fromthe screen with the mouse or using a region. Whenbuffering polygons, you can elect to generate thebuffer zones using setbacks on the interior or theexterior of the polygons.

You can generate multiple buffer zones in a singlepass with equal intervals or unequal intervals thatyou specify. You can elect to have your output ineither vector or CAD format and, if generating mul-tiple buffer zones, to save each individually or in asingle object. When generated in CAD format, mul-tiple buffer zones are drawn in different colors.

Note that the setting for saving multiple buffer zonesas a single or as multiple objects is in effect whenthe buffer zones are generated. Changing the set-ting after the buffer zones are generated but beforethey are saved does not affect the number of objectssaved.

input vectorresulting vector

buffer zones

resulting CADbuffer

zones


Separating Buffer Zones by AttributeIn this exercise, you will learn about separating bufferzones by attribute, transferring attributes, and us-ing a script to provide different buffer distances ac-cording to attached attributes. Separating bufferzones by attribute means that you get separate bufferpolygons for elements that have different values forthe selected attribute. Buffer zones for differentattribute values often overlap. If saved in vectorform, these areas of overlap must be resolved tomaintain polygonal topology. When saved in CADform, you get a separate polygon or multi-polygonelement for each attribute value. When generatedwith the parameters used in this exercise, you get asingle polygon for the portion of the perennial streamyou extracted and a multi-polygon element made upof seven polygons for the intermittent streams.

Vector buffer zone polygons will have more thanone record attached when transferring attributes ifthe polygon was created from overlapping bufferzones with different attributes. CAD buffer zoneswill have the same number of records attached asthe element they were generated from.

STEPS

set the Buffer Type toSingle, then click theSource tab and select ByScript from the Distanceoption menu, click onthe Specify icon to itsright, then on theOpen icon; chooseOpen FIle (*.qry),

select BUFZONE.QRY, andclick [OK] in the ScriptEditor window

select By Attribute fromthe Separate menu andturn on the TransferAttributes toggle

click on the Specifyicon to the right of theAttribute field, and selectClass for the Table andDescription for the Field,then click [OK] in theSelect Table/Field window

click [Apply]

click on the Select tool inthe View window

click on the bufferpolygon around one ofthe thinner lines, note thatall polygons aroundthinner lines are high-lighted, and that intermit-tent stream or wash isthe single attachedattribute

click on the Parameterstab and change theTarget to Vector, click[Apply], then click [No]

click on the LayerControls icon thenopen the CLASS table in thepolygon database

click on a number ofpolygons and note theattached attributes

CAD output

vector output

vector input


STEPS

choose Geometric/Combine

set the Operation optionmenu to Intersect (AND)

click on [Select] in theSource panel andchoose CBSOILSEXTRACT

from the VAO Project File

click on [Vector] in theOperator panel, andchoose the BUFFERZONE1vector you made in theexercise on page 7

click on [Run], select theProject File with yourbuffer zone output andchange the last 7 lettersof the default name toINT_ALL

when the processfinishes, set the secondSelect option menu inthe Operator Panel to ByElement

click on [Select]

left-click in the largebuffer zone polygon,then click on [Accept]

click on [Run], select thefile with your previousoutput, and change thedefault name to end withINTERS

view yourresults inthe Displayprocess

Vector Combinations: Intersect (AND)The Vector Combinations process lets you combinevector objects mathematically by georeference (orobject coordinates if georeferencing is absent).Combination by geographic extent is a very pow-erful feature that lets you admix vector objects cre-ated at different scales and in different map projec-tions into a single vector object.

There are two types of input objects for vector com-binations: the source and the operator. Simplisti-cally, the operator can be thought of as a cookiecutter and the source as the rolled dough from whichthe cookies will be cut. There are many differentcombination operations; in some the output is thecookie, in others it is the dough from which thecookie has been re-moved, in still others,it is both the cookieand the surroundingdough. The vectorcombinations processincludes 14 differentoperations so there aremany variations onthis simplistic descrip-tion. Our first opera-tion will produce thecookie as output. Youwill run the processtwice, once with alloperator elements selected and once with only thearea that falls inside the buffer zones selected.

source operator geographic overlay

result (All)

result (without islands)


STEPS

repeat steps 1, 3, and 4from the previousexercise (if you exitedthe process)

set the Operation optionmenu to Union (OR)

set the second Selectoption menu in theOperator panel to All

click on [Run], select theProject File with yourIntersect output, andchange the default nameto end with UNION

when the processfinishes, set theOperation option menu toExclusive Union (XOR)

set the Select optionmenu in the Operatorpanel to By Element, andclick on [Select]

click on the large bufferzone polygon, then clickon [Accept] (or Cancel ifthe polygon is alreadyselected)

click on [Run], select theProject File with yourprevious output, andchange the default nameto end with XOR

view your results in theDisplay process

Union (OR) and Exclusive Union (XOR)Some vector combinations are best explained byset theory. The sets are defined by elements andtheir geographic positions. The three set opera-tions available in the Vector Combinations processare Intersect, Union, and Exclusive Union. The re-sults from all three of these operations may haveelements and attributes from both the source andthe operator.

The Union operation produces the same results asAdd with resulting elements having attributes fromthe source, the operator, or both. The results of theIntersect operation appear the same as for Extractand Clip, however, attributes from the operator areassociated with the output for the Intersect (or Add)operation and are not associated with the elementsfrom Extract operations. The Exclusive Union op-eration is the inverse of Intersect with output ele-ments coming only from the area where the sourceand operator do not overlap. As such, individualoutput elements will have attributes from either thesource or the operator, but not both.

When viewing the results, note the effect of notselecting the island polygons in the buffer zone forthe Exclusive Union operation. How would theresults have differed if all operator elements hadbeen selected? (Check your prediction if you’renot sure.) Would selecting only the buffer zonepolygon and not its islands effect the elements out-put for the Union operation?

Union Exclusive Union


Subtract OperationThe Subtract operation removes source elementsthat fall within the area of the operator. The out-put object does not have attributes contributed bythe operator, because there are no elements left inthe area of overlap to attach them to. The Subtractoperation is generally used to remove elements inpart of an object prior to updating. With the vectorset used in this example, you might want to re-move the soil polygons in the buffer zone area be-fore merging the result with the hydrology used tocreate the buffer zones.

The decision of whether or not to include islandswhen applying the Subtract operation, as well asother operations, depends on your intended lateruse for the data and also likely on the size of theislands themselves. Islands are easily selected byquery (Internal.Inside==1 to select island polygons).You can build up a selected set of elements fromthe source or operator by combining one or morequeries and mouse click selections after choosingBy Element as the selection method. To build sucha selection set, be sure that the selection mode iconin the Select Element View window is set to ToggleMarked rather than Exclusive.

STEPS

choose Geometric /Combine [if you didn’t exitthe Vector Combinationsprocess after theprevious exercise, youneed only change theOperation to Subtractbefore you click on Run(step 8)]

set the Operation optionmenu to Subtract

click on [Select] in theSource panel andchoose CBSOILSEXTRACT

from the VAO Project File

click on [Vector] in theOperator panel, andchoose the BUFFERZONE1vector you made in theexercise on page 7

set the Select optionmenu in the OperatorPanel to By Element

click on [Select]

click on the large bufferzone polygon, then clickon [Accept]

click on [Run], select theProject File with yourbuffer zone output andchange the default nameto end with SUBTRCT

view your results in theDisplay process

islands notselected as partof operator

islands includedin operator

Subtraction results withand without islandsincluded in the operatorare shown at the left(although you are onlyinstructed to run theSubtract operationwithout the islands forthis exercise).


Extract OperationsThe Extract operations differ from most other opera-tions in the Vector Combinations process by usingthe operator only as a cookie cutter and not as asource of elements or attributes. You will, however,get line elements from the operator if the operatorextends beyond the source and you choose one ofthe Add Border options.

The options you choose, as always, are determinedby the use you want to make of the result, but when

STEPS

set the operation toExtract Completely Insidein the Vector Combina-tions window

select the same sourceand operator used in theprevious exercise if youhad exited the process

limit the selected operatorelements to the bufferzone polygons (steps 5–7 in previous exercise) ifyou exited after the lastexercise

set the Line and Labeloption buttons to None

click on [Run] and namethe output ECI

when the process isdone, change theOperation to ExtractPartially Inside, click on[Run], and name theoutput EPI

when the process isdone, change theOperation to ExtractCompletely Outside, clickon [Run], and name theoutput ECO

when the process isdone, change theOperation to ExtractOutside and Add Border,click on [Run], and namethe output EOAB

click on [Remove] in theSource panel

ExtractCompletelyInside

your source object is polygon data,you likely want to turn off selec-tion of lines and labels. The resultmay include labels not associatedwith polygons and lines that origi-

nally formed part of a polygon boundary if you don’tturn these selections off.

This exercise does not have you do all eight extractoperations, but you can certainly try them all if youare curious. Extract Outside and Clip has purpose-fully been omitted because the results are exactlythe same as for the Subtract option used in the pre-vious exercise. Also recall that the results for Ex-tract Inside and Clip are the same as for Intersectexcept the former result has attributes only from thesource, while the latter has attributes from both thesource and operator.

ExtractCompletely

Outside

Extract OutsideAdd Border

ExtractPartiallyInside


Using Lines as the OperatorSTEPS

set the operation in theVector Combine processto Intersect (AND)

click on [Select] in theSource panel and chooseHYDROLOGY from the VAO

Project File

click on [Vector] in theOperator panel andchoose ROADS from the VAO

Project File

choose Line from theOperator element typeoption menu

check that the TableJoining Options menu isset to If Same TableName and Structure

click on [Run] and namethe output objectLINETOLINE, saving it to thesame file you’ve beenusing for new objectsgenerated by theexercises in this booklet

examine your results inthe Display process; clickon New, choose 2DDisplay, select yourresults, open the LayerControls, click on [Styles]

on the Object paneland selectPointStyle from theVAO Project File,click on the Pointspanel and set Styleto By Script, clickon the Open icon,choose Open File(*.qry) and selectthe POINTS.QRY file,click [OK] in theScript Editor andVector LayerControls windows

Two of the vector combination operations, Inter-sect and Union, allow selection of lines as the op-erator. Intersecting operator lines with points, lines,and / or polygons from the source produces an out-put object that contains points, each of which rep-resent the location where an operator line crossesan element in the source. Using the vector objectsprovided in this exercise, the resulting points havetwo records attached from the Class table. One ofthe records identifies the road type where the hy-drology and roads intersect, the other identifies thehydrology class. You could also choose not to jointhe tables. You would then end up with a Classand a Class1 table, each with one record attachedto each point.

A style object and a query file are included in theVECTORAN directory to demonstrate assigning draw-ing styles using both of the attached attributes. Inthe script, symbol shape and size are determined bythe attached hydrology attribute and symbol coloris determined by the road type. The style object isnecessary because styles are specified by name inthe script.

vectors used forline to line intersect

output points usingstyle object andquery provided


Merge Overlapping Vector ObjectsSTEPS

choose Geometric /Merge to / Vector

click on [Select] andchoose the ROADS,RAILROADS, and MISCELLA-NEOUS objects in theNE_DLG Project File

check that the TableJoining Options menu isset to If Same TableName and Structure

check that RemoveUnattached Records andRemove DuplicateRecords are toggled on

click on [Run], accept thedefault name, and save itto the same file you’vebeen using for newobjects generated by theexercises in this booklet

examine your results inthe Display process(choose style from theline Style option menu)

You can choose any number of vector, CAD, re-gion, or shape objects to merge into a single vectorobject. All database tables associated with the in-put objects are transferred to the output, with theoption to join tables if they have the same struc-ture. You also have the option of removing recordsnot attached to elements from all tables and dupli-cate records from joined tables during the process.

The Merge process lets you choose the elementsyou want to include and the region you want to usefrom each of the input objects. If a subset of ele-ments is desired, it can be selected by attribute, byscript, or using the interactive selection tools. Themethod of selection can be specified differently foreach element type and object if desired. The re-gion to use can also be different for each input ob-ject. Thus, you do not need to extract your vectorsbefore merging them; it can be done as part of themerge process. The defaults are to select all of eachelement type with the full extents for the region. Ifyou want to extract as part of the merge process,

Three objects are merged so thatthe roads, railroads, and landingstrip are all in one object.

railroads

landing strip

roads

remember to set these options for eachinput object.


The Sourceobject isgeoreferenced toLat / Lon and theOperator to UTM.

Source

Operator

result ofReplaceoperation

Replace OperationSTEPS

choose Geometric /Combine

set the Operation optionmenu to Replace

click on [Select] in theSource panel and choosethe HIWAYSSTATEBOND objectfrom the NE_DLG ProjectFile

click on [Vector] in theOperator panel andselect the MERGE objectyou made on p. 14

click on [Run] andname the outputobject REPLACE,saving it to the fileyou’ve used for newobjects throughoutthis booklet

examine yourresults in the Displayprocess (choose stylefrom the line Style optionmenu)

The Replace operation uses the operator to replacethe area of the source that falls within the (selected)polygons in the operator. The source object isclipped where it meets the operator, and all sourceelements that fall within (selected) operator poly-gons are removed. As with other vector analysisoperations, the input objects need not all be in thesame map projection to get correct geographicplacement of selected elements.

In this exercise we use the Replace operation tointroduce a small area of greater detail into a largermap. Currently, theReplace Operationonly incorporates Op-erator polygons intothe output. For manyobjects, such as thatchosen for this exer-cise, all the lines hap-pen to be part of poly-gons, so the lines andtheir attributes are inthe result.


Merge Adjacent Vector ObjectsSTEPS

choose Geometric /Merge to / Vector

click on [Select] andchoose CBSOILSEXTRACT

then CBSOILSEXTRCT2 fromthe VAO Project File

check that the OutputReference System isGeographic, the TableJoining Options button isset to If Same TableName and Structure

check that the RemoveUnattached Records andRemove DuplicateRecords buttons aretoggled on

click on [Run] and namethe output MERGE2, savingit to the same file you’vebeen using for newobjects generated by theexercises in this booklet

examine your results inthe Display process(check that allpolygons areselected fordisplay byattribute[ClassStyle])

You can use the Merge process to combine vectorobjects that represent different data layers, such ascounty boundaries, transportation, and hydrology.You can also merge adjacent objects as we do inthis exercise.

Vector objects that represent adjoining ground ar-eas are likely to have elements on either side of theboundary that represent a single entity, such as asoil type polygon split at the edge of a soil map, orroads or hydrology that continue from one map quad-rangle to the next. You can create single polygonsfrom such split polygons provided both have theircommon attributes stored in a database table withthe same structure as demonstrated in the next exer-cise. Lines that continue from one map to anotherwith identical attributes are automatically joined intoa single line when the topology is validated as thelast step in the merge process (unless a node is re-quired because another line emerges at the junc-tion). If lines that are a continuation of one anotherare offset and do not join when you run the Mergeprocess, use TNT’s Editor to join the lines end to

end then run the RemoveExcess Nodes filter andreshape the line acrossthe gap if needed. (Seethe later exercise GettingMismatched Lines toMeet.)

The style objectis copied fromthe first selectedobject.


Dissolve PolygonsThe Dissolve Polygon filter lets you select one ormore attributes to use in evaluating whether thepolygons on either side of a line should be joinedinto a single polygon. We will use a single attribute,soil class, in this example. Once the vector objectis selected, all of its tables are listed in the lefthandlist. As you click on tables in the list, all of thefields for the highlighted table are shown in themiddle list. There is also an <<All>> choice if thetable has more than one field. If you click on<<All>> the attribute values for every field in thetable must be the same for two adjacent polygonsto be merged.

You can select asmany fields from asmany tables as de-sired. A commonreason to dissolveboundaries betweenadjacent polygons isto join polygonsthat were split be-cause they wereoriginally on separate maps or one was initiallymisclassified. You can also make a significantlydifferent map by choosing an attribute that is notdirectly related to the original polygon boundaries,such as dissolving soil class polygons by suitabil-ity as wildlife habitat.

STEPS

choose Geometric / Filter

click on [Select] andchoose the merged soilmap you made on p.16

click on the Add Filtericon, choose Dis-solve Polygons, thenclick on the Show Detailsicon if details are notshown

click on CLASS in theTable list, then on Class

Merged vectors have lines that mark the edges of theinput vectors (left),which can be dis-solved if the polygonson either side of theline share attributes(center). You can alsouse this filter to re-configure a map usingsome other attributethan initially used togenerate the polygons(right).

in the Field list, andthen on [Add-->]

click on the AddFilter icon andchoose RemoveExcess Nodes

click on [Run],name the outputDISSOLVE, saving itto the same file

click [View LogFile] in theStatus windowwhen theprocess is done,

note the numberof lines and nodesremoved, then click[Close] and [Exit]

examine your results inthe Display process


Getting Mismatched Lines to MeetSTEPS

choose Main / Edit

click on the Add Ref-erence Objects iconand select the REFERENCE

LINE object from the VAO

Project File

click on the OpenObject for Editingicon and select theMERGED_WITH_GAP vectorobject in the same file

click on the Snapicon in the Opera-tions panel of the VectorTools window

set the Snap To option toNode, Snap From to BothVertices, and Snap Typeto Add Vertex

zoom up until you can seeone of the gaps clearly

set the Snap Distance to300 Vector Units

click on the line on theright of one of the gapsthen click on Apply Oper-ation to [Active] or right-click; repeat for the othertwo gaps

click on the RemoveExcess Nodes iconin the Filters panel of theVector Tools window andclick on [All], or right-clickon the editable layer in theLayer Manager andchoose Remove ExcessNodes

Merged vectors often need a little editing to makelines that cross seams meet as they should. Theobject provided for this exercise has three gaps thatshould be joined. If you join two lines by movingthe endpoint of one, in this case using the snapoperation, you don’t need to concern yourself withassigning attributes, as you would if you add a lineto bridge the gap (if attributes are the same on eitherside of a node, removing excess nodes makes thetwo lines into one).

A reference line in CAD format is provided so youcan easily locate the lines that should be joined (thepositions and enlargements of the gaps are shownbelow). The Snap Distance can be specified in anyof the standard distance units or in pixels or vectorunits. If specified in pixels, the actual distance var-ies depending on the zoom factor. You can alsochoose the Edit function and drag the unattachedvertex of one of the lines to meet the other. Consultthe Editing Vector Geodata booklet for more infor-mation on editing vector objects.

You work with both ofthe windows shownand the Editor Viewwindow to edit vectorobjects.

Find and edit thethree gaps that fallalong the referenceline.

oddbehav-ior#20063


Polygon Fitting

ce2000t.MAL2FEM > 100

Distance Factor 0.10

STEPS

choose Geometric /Compute / Polygon Fitting

click on [Input Vector],select the vector in theENGCOAST Project File, andset the method toMinimum Polygon

click on the LayerControls icon in theView window if theLayer Manager windowis not open

expand the vector layerthen right-click on thepoints row and chooseMark by Query

on the Script panel* enterthe query exactly asshown, and click [Apply]in the Mark Points byQuery window

type 0.05 in the DistanceFactor field and click[Apply] in the PolygonFitting window

note the result, then type0.1 into the DistanceFactor field, and click[Apply]

note the difference

keep this process openfor the next exercise

Distance Factor 0.05

The Polygon Fitting algorithms were originally de-veloped to identify animal home ranges (polygons)from large numbers of observation points. PolygonFitting can readily be applied to point observationsfor a variety of other applications, such as epidemi-ology and archaeology. TNTmips provides a num-ber of different methods and parameters that deter-mine how the polygons are generated.

The Polygon Fitting process works either on allpoints or on selected points. If any points are se-lected, they are automatically used as the points forfitting. Your points may be observations of a singletype, such as a single animal or a single year of aparticular disease outbreak, or they may representobservations of multiple types, such as a number ofanimals or years of disease reports.

The database information used for selection in thisand the next two exercises is from the National Atlasof the United States web site (http://nationalatlas.gov). The database tables include the FIPS code foreach county record so they can be related to anyvector object that has a table with the FIPS codefield as the primary key. In this exercise, you select

the points where themale population ex-ceeds the femalepopulation. Inter-estingly, this occursfor only 309 of the1500 points.

* You can also use theBuilder panel to constructthe query.


Separating by Attribute in Polygon FittingYou look at the spread of West Nile Virus (WNV)from 2000 to 2001 in this exercise. In order use theSeparate by Attribute feature to polygon fit sepa-rately to the occurrences in 2000 and those in 2001,the data required some massaging, which was doneby adding virtual fields to the National Atlas tables.First you want to select only those points that rep-resent occurrences of WNV. The National Atlas fieldthat reports the occurrences of WNV is a string field,but we need a numeric field to easily select those

points where WNV occurred,so we use the StrToNum func-

tion, which returns the numerical value of a stringwith numbers and zero if the string is not a number.

The data for 2000 and 2001 are in separate tables,but Separate by Attribute works on a single field ina single table. A second virtual field was added tothe 2000 table that contains the year of the WNVoccurrence reported. To incorporate a new year anduse it for polygon fitting separated by attribute,you can simply copy or link to the new table directlyin the Polygon Fitting process, edit the definition ofthe new table to include a virtual field that convertsstrings to numeric values, and add to the script forthe virtual field that returns the year.

STEPS

turn on the Separate byAttribute and TransferAttributes toggles

click on the Specifybutton to the right ofthe Attribute field

click on WNVHUMT in theTable column and WHEN inthe Field column, thenclick [OK]

change the queryin the Mark Pointsby Query windowto be exactly as shown,and click Apply in thatwindow

type 0.5 in the DistanceFactor field, change SaveOutput As to Vector, andclick [Apply] in thePolygon Fitting window

note the result, then type0.25 into the DistanceFactor field, and click[Apply]

note the difference

click on Save As andname the objectWNV20002001

note that there is nowanother vector layer inthe Layer Managerwindow

show details for the topvector layer, open theWNVHUMT and W01HUMT

tables

(w01humt.StrToNum > 0) or(wnvhumt.StrToNum > 0);


Point Density RastersA point density raster is a reflection of the distribu-tion of points within a vector object. You may lookat point data that covers a wide area and see nearlycontinuous coverage. However, if these points rep-resent some naturally occurring feature or phenom-enon, rather than a regular sampling, there will beareas where the points are denser than others.

A point density raster is created from a collection ofvector points by determining the number of pointsthat fall within a specified radius of each raster cell.The points may either simply be counted to producethe cell value or an attribute can be specified to pro-vide the value for each point. Using attribute infor-mation rather than a raw point count may or maynot change how the density raster appears, but itcertainly will change its cell values. Be sure toconsider the potential values for the sum of pointattributes within the designated radius when choos-ing your output data type.

The ideal radius will find at least one point for eachcell within the extents of the points and more thanone for most cells. You want the smallest radius thatleaves no holes within the area of point coverage. Ifyou want to compare point density rasters for differ-ent attributes of the same points, you may have tocompromise on a radius that produces some holes.The radius should always be larger than the cellsize. For more details on this process, consult thecolor plate entitled Point Density Rasters on Micro-Images’ web site.

STEPS

choose Geometric /Compute / Point DensityRaster, click on [InputVector] and select theEastandGlfCoast vectorfrom the previousexercise

set the Value to Table,click on [Specify], andchoose CE2000T in theTable column andPOP00SQMIL in the Fieldcolumn

change the Units option tokilometers, then changethe radius to 60

change the Data Type to16-bit unsigned

click on Run and namethe output POPDENSITY

click on [Specify] for thevalue and selectcrimesp020.MURD00

compare your results inthe Display process

Population densityby county in 2000

This National Atlasdata was extractedto be usable inTNTmips Free.

Murders bycounty in 2000


Use these option menuswhen you want to limit theelements selected forprocessing to those withparticular attributes, thatsatisfy a specific query,or are selected fromdisplayed elements.

Element and Area SelectionVector analysis operations in TNTmips let you se-lect a subset of elements or a specific area for use inthe operation. This exercise provides a few point-ers on element selection and area specification, par-ticularly with reference to regions.

When you want to limit the area selected for a vec-tor operation, make a selection other than Full fromthe Region option menu and click on the Selectbutton to define the limited region. When you wantto restrict the elements selected within the desig-nated region, choose the desired option from theelement option menu and click on Select. You cancombine selection by query with mouse selectedelements if you choose By Element and apply thequery from the Element Selection Layer Managerwindow, then use other selection tools.

Use this option menu whenyou want to limit the areafrom which elements areselected for processing.

STEPS

choose Geometric /Extract to / Vector

select the HYDROLOGY

object from the VAO

Project File

set the Region optionmenu to Clip Inside andclick [Select]

pull out a rectangle in theupper right

click on Include inExtraction Area icon

click on the Circletool icon and draw acircle in the upper middle(overlap the rectangle alittle)

click on Include inExtraction Area icon

click on the Regiontool then on the AddRegion icon andselect the smallestbuffer zone you made inthe exercise on p. 7

click on the Include inExtraction Area iconthen on [Accept] inthe Select Regionwindow

click on [Run], andaccept the default name

Extraction area with inputobject for reference

Extraction areaalone

You can use as many of the toolsas you like while building up theextraction area. Just be sure toclick on the Include in ExtractionArea icon after drawing a compo-nent you want to add to the area.You can change the color andthickness of the extraction areaoutline using the Layer Controls forthe region layer.


Grid AnalysisGrid Analysis provides a flexible means to partitionpolygons. Grid analysis can be used for samplingprocedures in agriculture, ecology, forestry, biology,and related renewable resources. Partitioning subdi-vides larger existing polygon area(s) into smaller regu-lar sample polygon cells. These smaller cells can thenbe used as a graphical structure to which attributescan be attached to represent discrete geo-samplescollected at many points within the larger polygons.

Precision farming involves managing different partsof each field differently. To achieve this end, youdivide each field into smaller subfields, or manage-ment zones. The practical approach to determiningthe size of these zonestakes into considerationthe accuracy of yourGPS device, the re-sponse time of your vari-able rate applicationequipment, what you canafford in terms of sam-pling, and even the widthof your normal applica-tion equipment. The size ofyour management zone de-termines your managementresolution, which can be in-creased or decreased depending on yield results.

There are a number of different cell shapes to choosefrom for your grid. Hexagons are probably best formanagement zones; they better represent the aver-age values for attributes associated with an area.The orientation tool lets you set the direction of thegrid cells to align with a field boundary.

Once your grid is generated, you can create samplepoints within the grid at the center or randomlypositioned within the cell. Use these coordinates todirect your collection of soil samples, yields, andother data.

STEPS

choose Geometric /Compute / Grids

choose Source ByPolygon and selectBOUNDARY from the BORDER

Project File

on the Cell Shape panel,choose Hexagon for theCell Shape

set the units for the AreaParameter to acres,enter 0.25, and click on[Apply]*

click on [Save As]

Generating the points (notshown) using Geometric/

Compute/Sample Pointsprovideslocations forcollectingsamples in eachof the polygons.

* turn this toggle onbefore clicking [Apply]


Grids for ExtractionSTEPS

choose Geometric /Compute / Grids

set Source to MatchObject and selectCBSOILS_LITE from theCBSOILSGRID Project File

on the Cell Shape tabbedpanel, set theArea Param-eter to acresand enter 400

click on[Apply], then[Save As]

chooseGeometric / Attributes /Transfer Attributes

click on [Source] andchoose CBSOILS_LITE, thenon [Destination] andchoose the grid yousaved in step 4

set the Operation toPartially Within, and click[Run], then [OK], and[Exit]

choose Image / Extract,and select _16BIT_RGB

from the CB_COMP ProjectFile

on the Extract tabbedpanel set Select to ByPolygons, choose thevector from step 7, andselect a field from theGRIDENUM table as theattribute for defaultnames

click on [Run], selectyour output file, then clickon [Auto-Name]

view your results (bothraster and vector) inDisplay being sure toview vector attributes aswell

You can create a grid for use in extracting piecesfrom a raster or other object type. You might, forexample, want to extract TNTmips Free-sized piecesfor reference use in the field. A rectangular grid isrecommended for extracting rasters so that largeareas are not left as null. You can, however, createhexagonal rasters if desired for effect.

You can use all of the poly-gons in the grid for extractingor you can select certain poly-gons by query or with themouse and extract only the ar-eas underlying those grid

polygons. You choose one attribute to provide thedefault names for the extracted objects, which youcan modify if desired.

Six of the gridpolygons wereselected toproduce the sixseparate rasterobjects showntogether incorrectgeographicposition below.

This exerciseshould create 24separate rasters that, whendisplayed together, look likethe upper left of the originalraster. You can alsoexperiment with choosing alimited number of polygons forextracting by clicking on theModify button.

turn on this option


Grids and Surface PropertiesSTEPS

choose Geometric /Attributes / SurfaceProperties

click on [Input Raster]and choose OTOE_DEM_CLIP

from the BORDER ProjectFile

click on [Input Vector]and choose the vectoryou generated andsaved on p. 23

set the Reference Levelto 1096, and click on Run

click on [OK] for both ofthe table naming prompts

click on the LayerControls icon in theView window

expand the grid cell layer,and its lines andpolygons, then open theLINESURFACEPROP andPOLYSURFACEPROP tables

choose Select from theTool menu in the Viewwindow and examine thesurface properties forsome of the gridpolygons

The Surface Properties process computes 2D and3D properties for the lines and polygons in areas ofinterest designated by an existing vector object orby polygons you draw. In this exercise, you gener-ate surface properties for the management zones youcreated in the first Grid Analysis exercise.

Polygon surface properties are calculated relativeto a reference level (Z value) that you designate.Each cell on the surface is projected to a correspond-ing cell on the horizontal plane defined by the ref-erence level. The reference level is arbitrary; youcould pick the minimum or maximum elevation ofyour raster, sea level, or the median value, as donehere. Depending on your selection, polygons mayhave only a negative volume, only a positive vol-ume, or both positive and negative volumes.

Surface properties are also calculated for lines.These include surface length, which will be differ-ent than the length in the standard statistics tableunless the line has only a single Z value.

You have the option ofincluding or excludingislands from the surfaceproperties calculation. Youcan run it both ways ifdesired.

The BoundMinSlope and BoundMaxSlopefields report values for all the lines that boundthe selected polygon.


Vectors and SurfacesSTEPS

choose Convert / 2DVector to 3D Vector

click on [ReferenceRaster], and selectDEM_16BIT from theCB_ELEV Project File

click on [Select] andchoose HYDROLOGY fromthe VAO Project File

click on [Run] andsave the object in thesame file you have beenusing, then Exit

choose Main / Edit andopen the object you justsaved for editing

expand the layer andright-click on the line row,choose Mark by Query,enter Internal.MinZ==0,and click Apply

click on EditElement, then on [Edit]

toggle on ManualEntry, find a vertexwith Z of 0 (first or lastgenerally), click Delete*,then click [Save]

click on the NextMarked icon, then on[Edit], repeat step 8 andthis step until all Z of 0vertices have beendeleted (reapply thequery to be sure)

save the result

There are two kinds of 3D vectors: 3D X-Y and 3DX-Y-Z. Contour or other isolines are 3D X-Y vec-tors—the Z value for the line is constant and is notstored with each vertex of the line. Vectors with Z

values that vary fromvertex to vertex are 3DX-Y-Z vectors, whichmeans that all three co-ordinates are stored foreach vertex. Both kinds

of 3D vectors can be used as input for the SurfaceModeling process, which generates elevation ras-ters. 3D X-Y vectors are generated by the Contour-ing operation in the Surface Modeling process.

Elevation rasters can be used to assign Z coordi-nates to a vector from the cell value at each point orline vertex. It often turns out that the extents of theraster and the vector are not quite the same. If theextents of the raster are smaller than the vector, thereis a question of how to assign Z values for elementsoutside the raster area. The process lets you enter avalue to be assigned to all such elements. The low-est value in the elevation raster might be a goodchoice or you can leave it at zero and take care ofany problems in the Editor. In this exercise, a fewlines have their end nodes outside the raster. Leav-ing the outsidevalue at zeromakes theselines easy toidentify.

* Alternatively, youcould change the Zvalue to that of the closestnon-zero vertex.


Other Analysis ProcessesThere are a variety of other processesavailable in TNTmips to assist invector analysis. Standard attributesand fuzzy properties can be gener-ated and stored in database form withthe vectors for use in selection anddisplay or in other processes, suchas Network Analysis.

The Directional Analysis process(also called Lineament Analysis)provides a statistical analysis, whichis displayed as a rose diagram, of thedirectional properties of the lines in an object. Anumber of different methods for computing thesestatistics are provided. You can also create a newvector object containing only those lines that havethe specified directional prop-erties.

TNTmips also has a process tocreate distance rasters fromvector objects with cell valuesthat represent the distance fromthe selected vector elements.The raster surface produced canbe planar, a DEM, or a cost ras-ter (the latter two require reference raster input).These rasters can, in turn, be used as input for theGradient Descent Path process or to generate re-gions that are greater than a specified distancefrom the elements used to generate the distanceraster. You can also generate regions less than aspecified distance from these elements, but thatis just as easily accomplished using buffer zones.

You can view allrecords or only therecords associatedwith selectedelements in tabularview. Single recordview shows therecord associatedwith the activeelement only.

Rose diagram using theNode to Node method forDirectional Analysis on theHYDROLOGY vector used in anumber of exercises in thisbooklet (shown on facingpage).

This distance raster was generated from the samehydrology vector object used to create the rose

diagram, above, and for generation of the two tablesshown above.

distance raster

Advanced Software for Geospatial Analysis

MicroImages, Inc.

VECTOR

ANALYSIS

11th Floor – Sharp Tower USA

www.microimages.com

Index3D vectors ...................................... 4, 5, 26area selection .......................................... 22buffer zones .......................................... 7–8directional analysis ................................. 27dissolve polygons .................................... 17distance raster ......................................... 27editing vectors ........................................ 18exclusive union (XOR) ........................... 10extract operations .................................. 12Extract Vector ................................... 6, 22filter log ................................................... 17fuzzy properties ...................................... 27gradient descent path ............................. 27grid analysis ...................................... 23–25intersection (AND) ........................... 9, 13line to line intersection ......................... 13merging vectors ............................... 14, 16mismatched lines .................................... 18National Atlas of the United States19–21network topology ................................ 4, 5object information ................................... 4

planar topology ................................... 4, 5point density rasters ............................... 21polygonal topology ......................... 3, 4, 5polygon fitting ................................. 19–20polygon properties ................................. 25regions ................................................. 6, 22remove excess nodes ....................... 17, 18replace operation .................................... 15rose diagrams ........................................... 27separating by attribute ...................... 8, 20snapping lines .......................................... 18standard attributes .................................. 27subtract .................................................... 11surfaces ............................................. 25–26table joining ................................. 9, 13, 14topology applications .............................. 5topology types .......................................... 4union (OR) .............................................. 10vector combinations .................. 9–13, 15vector filters .................................... 17, 18

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