geoportals for providing interoperability infrastructure · 2013-09-19 · of spatial data,...

GeoPortals for Providing Interoperability Infrastructure

FATĐH SARI, ALĐ ERDĐ Geomatics Engineering

Seljuk University Selçuklu, Konya

Turkey [email protected] http://www.fatihsari.selcuk.edu.tr

Abstract: -Accessing to the spatial data is one of the most prominent demands of the information age, which causes constituting information systems by institutes and organizations in local, regional and national scales. Together with the technological developments, raised process capacity with spatial data, considerable increase of spatial data quantity and developments of multi-disciplinary projects reveals the interoperability concept. Developments of national spatial data infrastructures provided implementation of spatial data standards largely and at the same time GeoPortal systems have become a functional and effective way for sharing and accessing spatial data instantly. GeoPortal system as defined a visible interface of national spatial data infrastructures provides effective solutions to the interoperability thanks to the innovations about sharing, serving and presenting spatial data. In this study, a GeoPortal design is constituted to provide Interoperability infrastructure for organizations and institutes, which produce/use spatial data. This GeoPortal is also an implementation of interoperability INSPIRE and ISO for spatial data. Technical structure of GeoPortal is an implementation of OGC and W3C technologies and standards.

Key-Words: - GeoPortal, WebGIS, Standards, Web Services, INSPIRE, Spatial Data Infrastructures

1 Introduction Nowadays, GeoPortal systems are extensively used to implement Spatial Data Infrastructures (SDI) at local, regional and National scales [1]. Because of GeoPortals are visible part of SDI’s and establish a bridge between users and SDI, it is considered as a continuous development systems and emphasizes the significance of SDI’s. In the early 2000’s, this growing importance has led to activities increased in the field of standards, interoperability, visualization of spatial data, metadata services, administrative policies and geodatabases to use SDI’s effectively [20].

SDI’s are interoperability infrastructure for spatial data management [7]. In SDI definition made by [10], “instant reaching to spatial data” expression is used. On the other hand, nowadays instant accessing to spatial data is no longer achieved by serving spatial data directly. Instead of this approach, web services are being served to the user. Thus, system designers could specify user demands by providing multi- web services from different data sources. In this way, providing quick, economic and high quality service to the users will be achieved with Service Oriented Structures (SOA). Basically, SOA structure is interactive working of sharing metadata and standardized web services to provide interoperability [5].

One of the main objectives of constituting SDI is

planning access tools to spatial data that will allow interoperability. The United States National Research Council’s Mapping Sciences Committee defined SDI in 1993 as a tool, which will provide the integration of attribute data and spatial data with daily phenomena. Committee also declared that technical infrastructure and processes, which allow users to access spatial data should be, exist in SDI structure [13], [20]. Referred technical infrastructure and entire processes are being GeoPortal systems.

GeoPortal Systems are generated to provide reaching, querying, visualizing functions of spatial data. There are many different GeoPortal definitions are available in literature and highlights “accessing spatial data via web” expression. BEA systems are defined GeoPortal as “a web site which is only one way to access spatial data and its applications” [6]. Java Portlet is defined GeoPortal as “personal or common web applications which are combining spatial data from different sources or data providers”. According to the ESRI, GeoPortal is “a system to access spatial data without depending to location, format and data types” [9]. Open Geospatial Consortium (OGC) defines GeoPortal as a “human interface to collect online spatial data sources, spatial datasets and services together” [16].

Recent Advances in Geodesy and Geomatics Engineering

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GeoPortal systems are divided into two groups as application and catalogue GeoPortals. Catalogue GeoPortals are working as a metadata provider or spatial data list that allows query inside spatial datasets [14]. With a querying system, a keyword could be queried inside SDI and matching spatial datasets are integrated into a list. Thus, the presence of spatial data can be displayed on web pages with its technical attributes (metadata). If required, users may be contact with data providers according to the information detailed in metadata. Nowadays, most of the SDI GeoPortals are working as catalogue GeoPortals.

Application GeoPortals are providing more functional interface, which includes visualization, advanced query tools, attribute data of spatial data, metadata services, Print services and Spatial Analysis. In application GeoPortals, users can be more interact with spatial data sets. Application and catalogue GeoPortals must worked together to provide interoperability in SDI [12].

In this study, A GeoPortal interface is constituted to access spatial data by considering international Standards. GeoPortal infrastructure, components related standard organizations and their directives are explained to establish interoperability. As an application GeoPortal, metadata service is integrated and component details are explained.

2 International Standards to

Constitute GeoPortal Infrastructure The need for spatial data and due to developing internet technologies, working with distributed databases, web service compositions, data sharing and accessing data is being more important for users in the concept of interoperability. On the other hand, these components are required standards in the field of produce, sharing, accessing and analyzing spatial data. Standards are the main object of interoperability concept in every field of establishment stage.

Standardization studies started in the field of spatial data in 1990. In 1991spatial data standard formation started with the name of CEN/TC 287 and this formation is still working as ISO/TC 211 in international area [22]. ISO/TC 211 Technical Committee is preparing standards for spatial data under 19100 Geographical data catalogue.

Open Geospatial Consortium (OGC) is one of the most important organizations that work for ISO/TC 211 standards more applicable. OGC members are developing essential technologies for

spatial data to use more effectively and provide interoperability.

Main aim of OGC is collecting institutes and organizations, which need for spatial data, inside a technical platform by constituting human interface and applications and providing all standards to be applicable. Standards are defining encodings, numerations and technical specifications and include service standards, which are prepared by ISO TC/211 independent from application platform. The standards, which include important specifications and definitions for interoperability, are available for everyone [8].

INSPIRE organization is working around Europe to define features that spatial data should have. Because of INSPIRE aimed to constitute European Spatial Data Infrastructure, specification and classifications are created by considering the structure of European countries. INSPIRE specifications are defining attribute information of spatial data, form and geometry of spatial data and enumerations and encodings of geographical features.

The World Wide Web Consortium (W3C) is an international organization working to create web standards with member organizations. The main aim of the W3C is developing protocols for full potential web and demonstrates the rules, which will provide and support long-term development of web [23]. 2.1 INSPIRE Infrastructure for Spatial Information in the European Community (INSPIRE), is founded in 15 May 2007 to establish European Spatial Data Infrastructure. INSPIRE is consisted from 27 member countries and 34 spatial data catalogue, which includes application technical Specifications and components. INSPIRE is defined spatial data catalogues to identify spatial data and applicable technical structure. Spatial data catalogues are also useful to specify working groups and prepare detailed specifications for spatial data. 34 spatial data catalogues are divided into three groups as Annex-I, II and III. Annex-I is 9, Annex-II is 4 and Annex III is including 21 spatial data catalogue and specifications. In each spatial data catalogue, enumerations, data types, encodings and attribute information are defined. 2.2 Open GeoSpatial Consortium OGC Standards are technical documents, which define Human interfaces and encodings. Software programmers are using technical details defined in technical documents when developing interfaces. These technical documents constitute the core object


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of OGC. OGC standards are developed to use in World Wide Web (WWW) applications [24].

OGC is using web services to provide using of spatial data via web pages. Every web service is forming a different standard of OGC. Although standards are similar to each other, service parameters, data types, request URL and interfaces are differs [17]. In Table 1, OGC web service standards are given. WMS, WFS and WCS are using to server spatial data through internet. These standards are differs in the field of spatial data format and functions. WPS is providing an infrastructure to analyze and process spatial data through internet and defines the protocols. SLD is an important standard for web services to specify symbology.

Table.1 OGC standards

WMS Web Map Service WFS Web Feature Service WCS Web Coverage Service WPS Web Processing Service SLD Styled Layer Descriptor

Each standard of OGC is defining requests to

interact with spatial data on web pages. Requests are also determining the function of processes and behave as like a bridge between server and client.

Each request has different parameters to retrieve spatial data from server and these parameters are explained in OGC standards. All of the request parameters are integrated into URL to start request-response traffic. OGC requests are,

GetMap: retrieve map from server with user defined parameters GetFeatureInfo: retrieve Attribute data of spatial data from server GetLegendGraphic: downloads Legend image from server GetCapabilities: downloads information about server capabilities

2.3 International Standard Organization

(ISO) ISO is developing Standards for Geographical Information to increase spatial data quality and provide spatial data sharing systems with ISO/TC 211 technical committee. In this concept, ISO is generating standards for sharing, visualizing, serving and retrieving spatial data. ISO TC/211 “Geographic Information/Geomatics” committee is

founded in 1994 with the support of Europe Standard Committee CEN- “Commité Europeen du Normes” ‘in CEN/TC 287 “Geographic information”. ISO Standards are divided into groups and ISO 19100 series is named “Geographic Information”. CEN/TC 287 defines first 20 standard name of ISO 19100. ISO is working with the combination of organizations, institutes, universities and personal corporations to develop Standards [2]. In Table 2 ISO Standards are given which can be used to develop GeoPortal. Applying Data Quality standard is important to establish usable and effective GeoPortal systems. Metadata is one of the vital component of GeoPortal systems to define spatial datasets.

Table.2 ISO standards

19115 Metadata 19136 GML 19138 Data Quality 19119 Services 19128 Web Map server interface

2.4 W3C W3C is developing Standards only to use in web applications. W3C aimed to develop quick, effective and user friend web concept without distinguishing Simple web Pages or advanced scripts [21]. In Table 3, W3C Standards are given which can be used to develop GeoPortal. HTML is used to specify components and facilities of GeoPortal and works with CSS files to define the visual effects and seem of web pages. HTML codes are also carrying the CSS and PHP codes to client computers. WSDL is important to define web service facilities for clients and web server users. XML is mostly used to generate web services, attribute data and related metadata transfer.

Table. 3 W3C standards

CSS Cascading Style Sheets HTML Hyper Text Markup Language SOAP Simple Object Access Protocol SVG Scalable Vector Graphics XML Extensible Markup Language WSDL Web Service Description Language XMLS XML Schema


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3 GeoPortal Components GeoPortal systems are consisting of a combination of several components. These components are server, client, software, hardware, spatial data and spatial data providers. Components are sharing the same technical platform by adapting them together with scripting technologies and building the whole system structure. Harmony of the components with each other, supports, demands and performance relevance issues are most important issues for GeoPortal system structure and should be considered before GeoPortal system design to provide high performance GeoPortal systems. 3.1 Server The core object of the GeoPortal is server computers. In the client/server programming model, a server is a program that awaits and fulfills requests from client programs in the same or other computers. In GeoPortal systems, all the interface encodings, scripts and source codes are stored in servers. Thus, updates, recovery processes and GeoPortal design should be performed in server computers. 3.1.1 Web Servers

Web servers responsible to deliver web content that can be accessed through the internet. Web servers usually use to host websites but also there are other roles such as database and application host. In GeoPortal systems, web servers are providing request-response traffic between server and clients [4]. 3.1.2 Spatial Data Servers

Spatial data servers (also referred as Geographical Data Servers) are creating web services of spatial data. Spatial data server is playing similar role with web servers. Spatial data servers only deliver the web services to the client computers. Because of spatial data server provides spatial data transfer in web service form, it is being an essential component of GeoPortal systems [18]. 3.2 Client Clients are the person or softwares that send requests to the servers to retrieve data or web page. In GeoPortal systems, clients are the GeoPortal users who need to interact with spatial data. Desktop, laptop, tablet pc and pda devices can be used as a client. Client computers are strictly needs internet connection. Thanks to the GIS software tools, it is possible to connect a server and view web

3.3 Software GeoPortal system structures are including several softwares, which are working on different platforms. Every GeoPortal components have different softwares and these softwares should be integrated each other. Softwares are divided into groups such as web design, web server, geographical data server, database, web browsers and operating system Softwares

3.4 Hardware Hardware has an effect on GeoPortal system performance directly. Both client and server hardware are important to realize GeoPortal processes. Because of most processes are being realized in client computers, processor and RAM capacity is playing an important role on system performance. 3.5 Internet Internet is providing the connection of client and server computers. Internet is carrying data for displaying web pages with using TCP/IP protocols. In GeoPortal systems, because all data is transferring with internet connection, internet bandwidth and connection speed relatively effect the GeoPortal system works. Server internet bandwidth should be enough to response each request coming from clients as fast as possible.

3.6 Metadata Metadata term refers to definition data about spatial data. Metadata is explaining and defining the spatial data according to the ISO 19115 metadata standards. ISO 19115 defines the attributes of spatial data in quality, status, data provider/producer; coordinate reference system and geographic coordinates of data frame [15], [19], and [3].

Especially in catalogue GeoPortals, when searching for a spatial dataset, user should know the characteristic features of spatial data. Thus, users can specify that spatial data is usable or not for the project. Because metadata files provide effective use and definition of spatial data, GeoPortal system should include metadata services. Metadata services should contain search engine to provide searching a particular name in spatial dataset. 3.7 Data Provider In GeoPortal systems, data providers are the organizations or institutes who produce or provide spatial data and its metadata file. Data providers are responsible from up-to-date and accuracy situations of spatial data. Data providers integrate their spatial


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data, which they responsible to produce to the GeoPortal systems. Because GeoPortal system can work with distributed databases, spatial data from different data providers can be easily integrated into GeoPortal system. 3.8 Users Users are the authorized person to connect to the GeoPortal system. Authorized person can connect and use the functions of GeoPortal system. User count, user software and hardware types, operating system platforms are effecting the performance of GeoPortal systems.

4 Constituting GeoPortal

Infrastructure GeoPortal system is a combination of softwares and programming languages. Due to GeoPortal system is running both server and client side, different softwares and programming languages are used. GeoPortal system operations and functions are mostly processed on client side. This situation is required to program with JavaScript language for client side operations. However, server side operations cannot be done with JavaScript programming language. Therefore, for server side operations, mostly Php language is used. For the human interfaces and forms that displayed in web pages are programmed with Html codes. Html codes are also carrying Php and JavaScript codes to the client computers and Css style files, which specify the style options of every visual object of GeoPortal.

In this study, a GeoPortal system designed with human interfaces to provide sharing, visualizing, viewing and analyzing of spatial data in accordance with international standards. Every components, processes and technical structure of GeoPortal system are designed considering the definitions and specifications of related standards for providing interoperability infrastructure. Thus, it is being possible to integrate different web services, spatial data and other services coming from other countries into GeoPortal. 4.1 GeoPortal Interface GeoPortal interface contains necessary tools to interact with spatial data and play a holder role for all toolbars and operation buttons. Interface involves map window to display spatial data, attribute table to view attribute data of desired geographic object in spatial dataset, legend window to display symbology and legend information of spatial data displayed on map window, information bar to

display coordinate system name and coordinate values of mouse cursor and map toolbar to interact with map window to change current view of map.

For the purpose of generating GeoPortal interface, existing GeoPortal and their programming technologies are examined. It is seen that, existing GeoPortal systems are developed by using ESRI GeoPortal Interface and Heron MC Javascript Library. ESRI GeoPortal interface is a catalogue GeoPortal system, it has limited visuality, and it is quite difficult to integrate new services or functions to ESRI GeoPortal. On the other hand, Heron MC Library is providing more flexible and open source development environment for GeoPortal functions. Adding new functions and integrate new services into Heron MC is possible and easy with its flexible structure. In Figure 1 and 2 ESRI GeoPortal and Heron MC interface are shown.

Fig.1 ESRI GeoPortal Interface

Both ESRI and Heron GeoPortal structures have

some advantages to interact with spatial data. In ESRI structure, users can search spatial data and preview it on map with metadata details. However, users cannot be display or select geographical objects in spatial datasets. ESRI is providing more common information for spatial datasets. Heron structure is more special and it has more functions to interact with spatial data. Heron can display attribute table, legend of data, metadata and its properties. Thus, Heron structure is suitable for special GeoPortals, which is related with categorized spatial dataset.

In this study, GeoPortal system is developed using Heron MC structure and it has 5 sections to implement international standards.


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Fig.2 Heron GeoPortal Interface

4.2 Spatial Data List Spatial data list, as shown in Figure as 1, constitutes a list of web services involved in GeoPortal system. This spatial data list is carrying the WMS or WFS URL’s of web services. Users can choose the spatial data by checking the box and web service will be displayed on map window. When user check the box of related spatial data, GeoPortal interface will sent GetMap request of related spatial data to the server. Server will be send the web service content to client computer and data will be displayed on map window.

For the purpose of constituting spatial data list, INSPIRE data specifications are considered. INSPIRE data specifications are proposed spatial data groups as defined in Annex-I, II and III. Thus, providing spatial data accessibility, implementing INSPIRE data specifications and integrating data by into GeoPortal by using INSPIRE specifications is being possible. Also considering INSPIRE specifications are providing users to view same data with same symbology and geometry type.

One of the most important objects in GeoPortal system is viewing the web service address. Because of spatial data not only usable in GeoPortal systems but also in GIS softwares, web services addresses should be open in GeoPortal systems to maintain interoperability. This will also prevent duplicated spatial data problem because of connecting to the same web service. 4.3 Map Map window is displaying the spatial data, which selected on data list. Web services are being visible on map window with its contents. Map window structure is developed by using Openlayers map library. OpenLayers is constituted by OGC to view

spatial data on web pages. In Figure 3, map window is shown.

Fig.3 Map Window

Map window is the main object of GeoPortal system and it is related with every component of GeoPortal. For instance, when user click on a geographical object on map, GetFeatureInfo request is sending to the server. Coordinates of mouse cursor on map will be displayed on info toolbar. Attribute table, legend window and other functions are started to working by user’s interaction with map window.

4.4 Legend Window Legend window displays the legend of spatial data, which is coming from server as a respond to GetLegendGraphic request. Legend of t spatial data is important for users distinguish the symbology of data and especially graduated colored raster data. Legend window is reading the Styled Layer Descriptor (SLD) file, which is related with symbology of spatial data. SLD is a standard of OGC and XML based file. SLD files are carrying symbology features and specify how data will seem. Especially in GIS softwares, there are several tools, which convert the symbology to SLD file. SLD is providing same symbology for desired spatial data. INSPIRE catalogues are also defining the SLD of data. 4.5 Info Toolbar Toolbar is being embedded to the map window to set view options. Toolbar have pan, zoom in, zoom out, view attribute table and measurement buttons. This buttons and related functions are providing quick management of map window. In Figure 4, toolbar is given.

2

1

3

5

4


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Fig.4 Info Toolbar

4.6 Attribute Data Attribute Table is a window, which shows the attribute data of selected geographic object form map window. When user clicks on an object, GetFeatureInfo request is composing by client computer and will send to the server. The respond is a XML file, which contains attribute data. If a spatial data is prepared by considering INSPIRE specifications, attribute data will be the same format. In Figure 5, attribute data seem is given.

Fig.5 Attribute data

The larger view of attribute data table is given in Figure 6. The columns are representing the spatial data attribute, which is same with spatial data.

Fig.6 Attribute data

Attribute table also supports GML format to

display attribute data in GML format. In Figure 7, attribute data window with GML format is given.

Fig.7 XML window

4.7 Metadata Metadata service is prepared according to the ISO 19115 metadata standard. In GeoPortal systems, it is important to support metadata support to the users. In Figure 8, metadata service and metadata window is shown.

Fig.8 Metadata interface

5 Conclusion Interoperability concept will be established in the case of establishing standardization processes of spatial data, providing accurate data and prevent duplicated data, integrating different SDI projects in one platform, updating data and understanding international standards by institutes and organizations.

The main object of establishing interoperability structures is standardization. This will be achieved if only organizations and institutes includes standardization processes both theoretical and practical area. It is clear that, establishing and developing GeoPortal systems are depends to the standardization processes. If standardization will be achieved at national scales, GeoPortal system will be the most convenient way to establish interoperability structure.


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Beside this situation, technical structure is being applied and integrated to many applications. Especially W3C and OGC standards are being applied and used in the field of accessing to spatial data. This is showing that, technical infrastructure is in good condition to establish GeoPortal systems. If spatial data standardized can be applied, establishing national GeoPortal systems will be possible which fulfills the demands of users.

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geoportals for providing interoperability infrastructure · 2013-09-19 · of spatial data,...

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