A Web-based Electrical GIS MapServer. Via. Open Source GIS Software

Transcription

1 A Web-based Electrical GIS MapServer Via Open Source GIS Software Post GIS Tanakorn Jangkakul Fall 2007 Geographic Information System University of Texas at Dallas

2 Table of Contents List of Figures Title.. 4 Introduction.. 4 Problem Statement... 5 Project Objective.. 5 Literature Review. 6 Data Source 10 Software. 13 Methodology.. 13 Result. 24 Conclusion. 25 Futurn Works. 25 Reference Appendix

3 List of Figures Figure 1: a Diagram of a Mapping Website Interacts with Programs Running on the Servers Figure 2: WMS Compliant MapServer Architecture Figure 3: Geometry Type Hierarchy Figure 4: an Example of Idaho Falls Electric Network Model including Electric Flow Figure 5: Overview of Idaho Falls Base Map Figure 6: Connectivity Table in Logical Network Figure 7: an Example of Connectivity Rule Interface in ArcGIS Desktop Figure 8: a Connectivity Table in Logical Network after Determining the Flow Figure 9: an Example of ArcObject Interface Figure 10: Exporting from geometric Network to Open Source Spatial Database Algorithm Figure 11: pgadmin III Interface to Assist User to Access into PostgreSQL Database Figure 12: Basic Operation of MapServer Figure 13: an Example of a Map Image Figure 14: an Example of Predicted Outage Devices due to One Customer 3

4 Title A Web-Based Electrical GIS MapServer via Open Source GIS Software Introduction Currently, Internet GIS, or distributed GIS, is an Internet-centered GIS technology that use Internet as the primary ways to access the data, conduct spatial analysis, and provide location-based services. The trend of Internet GIS has emerged to overcome several limitation of popular desktop GIS software by providing several advantages. For example, there is no need to install and maintain GIS software on every desktop, users can access to geospatial data and spatial analysis tools in any place with internet access at any time, which is not limited to the office as with desktop GIS software, and users do not need to purchase proprietary GIS application software because of the availability of many open-source GIS software, which provides a variety of different spatial analysis function as well as a open development environment (Figure 1), whereas most proprietary desktop GIS software need to be purchased and is inaccessible from locations other than the computer on which the desktop GIS installed. Figure 1: a Diagram of a Mapping Website Interacts with Programs Running on the Servers (Tyler, 2005) 4

5 In this fashion, electric companies also capitalized these advantages to provide Internet GIS Servers, such as outage management, which help the companies to reduce outage duration, decrease operation cost, raise revenue, increase crew accessibility, and enhance customer satisfaction. For example, when outage occurres, the utility companies not only have a difficult issue from perception, but also lose revenue because the electric is not flowed. Depending on the extent of the outage, the amount of revenue lost can be considerable. Problem Statement ArcGIS geometric network can determine the flow of electricity that assist the electric company to determine outage devices such as meter, circuit, secondary line, transformer, switch, and fuse via upstream tracing method. Is there any approach to export the relationship in geometric network so that it can be displayed on Internet GIS so that utility companies can predict location of outage devices using these exported data? Project Objective The purpose of this project is 1) to develop a methodology for the efficient conversion of electric utility data from a geometric network model in desktop ArcGIS to the postgis open source spatial database, 2) to develop an algorithm to allow the function provided by utility company to predict outage devices in map server, and 3) to display the geometric network stored in PostGIS online using MapServer. In doing so, the challenges of converting data from a proprietary, desktop-based system to an open source spatial database, and display the network on web-based system will be highlighted and explored. 5

6 Literature Review Kraak (2004) expresses broadly to the rule of map on the Internet GIS environment and states that maps have an important role to play in Web-GIS environment in both interactive and dynamic appearance. The maps also assist the users in solving geospatial analysis problems, and unlimited number of users can access the maps anywhere at all times. Further, well-designed Web map can help users to stimulate thinking about geospatial patterns, relationships, and trends. For example, blur gives symbol a fuzzy appearance and can be applied to visualize uncertainty. Blinking or highlight symbols are to attract attention. Transparency can be seen as a kind of fogginess where part of the map content is obscured or faded of other information. In addition, since Internet GIS is currently the medium to present and disseminate geospatial data and maps, which allows one to offer the spatial data and information independently and virtually unlimited number of users can access the map. However, there are still some problems to be solved. The performance of working in Web-GIS environment depends on several technological factors such as internet connection, traffic intensity, data efficiency, and the capability of client and server machines. Vatsavai et al (2006) discuss about MapServer that provides an important innovative architecture behind MapServer application. The main components of any web GIS is the client, the server, and the network. The initial response of the geospatial technology industry to the popularity of the internet by developing Common Gateway Interface (CGI) wrappers to their standalone GIS application. This design brings into the thin client and fat server system. 6

7 Figure 2: WMS Compliant MapServer Architecture (Ranga, 2006) MapServer follows standard 3-tier architecture of Web Map Service (WMS) Compliant. The three layers are the client, the server, and the geo-spatial database access system (GSDAS). The server layer is further subdivided into the CGI, geospatial analysis and communication subsystems. In this approach, the server will be overburdened with both geospatial analysis and data access, which may cause several disadvantages. For example, the number of users increase, the load on the server also increases and system performance will be decreased. Another reason is that HTTP/1.1 is a stateless and connectionless protocol. By connectionless, it means that the client and server are connected only for the duration of the transaction. Stateless implies that the server forgets about the client once after the transaction is over. The web client does not understand anything about geospatial elements. Therefore, in such system all of the data access and processing is performed on the server with the results being converted into an image (e.g. JPEG, GIF, or PNG) and passed to web client. To alleviate this drawback, a load balancing client/server approach would be presented by gradually shifted toward client-side GIS through client technology such as Java applet, JavaScript, ActiveX controls and extendible 7

8 Web Clients. This approach can decrease overload on the server called balanced client/server, which improves performance of web GIS data access. However, there are two critical factors to affect the performance of Web GIS: The bandwidth bottleneck of the internet, and the large volume of data to be transmitted in GIS and multimedia application. The performance can be improved by first, increasing the speed of Internet connection and second, developing more efficient applications. Since last five to six years ago, the network performance has increased dramatically. GIS developers have focused on the development of efficient algorithms to improve system performance such as presented a progressive vector transmission technique, presented a layer decomposition technique for spatial data transmission, presented a method for progressive transmission and rendering for 3D-GIS, and presented a method for fetching spatial data from spatial database. In addition, Ranga also discussed about MapServer interoperability. MapServer has ability to read various Open Geospatial Consortium (OGC) standard data types such as GML, shape file, mapinfo file, WMS, GeoTiff and more. Huang and Lin (2004) state that Web GISes commonly have been used for spatial data access, spatial visualization, and simple retrieval mapping. This lacks of analytic capabilities for GIS applications. In the Internet environment, the client usually sends a request to the server. The server processes the request and returns the result to the client. The well- designed spatial query language can perform as a guideline for the query process in Web GIS. Also, there are 2 main implementation approaches to query spatial feature in tables common SQL and SQL with spatial data. Spatial SQL introduces spatial data types (e.g. point, line, polygon, and image) and spatial operators (e.g. distance, direction, overlap, and contains), which enable user to inquire about spatial relationships. Further, each spatial feature is stored in a 8

9 row of table and maintained in a Relational Database Management System (RDBMS). Huang also described about geometry types followed by opengis standard. Figure 3: Geometry Type Hierarchy (Huang, 2004) The root type is named as geometry having subtypes of point, curve, surface, and geometrycollection. A geometrycollection is a geometry that is a collection of possibly heterogeneous geometries. Multipoint, Multicurve, and Multisurface are used to manage homogeneous collection of points, curves, and surfaces. Point and multipoint are zero dimensional geometric types. Curve and multicurve together with their subclasses are one-dimension. Surface and multisurface with their subclasses are two-demensional geometry types. In addition, as an implementation of opengis spatial SQL defines a subset of these geometry types including point, linestring, surface, polygon, multipoint, multilinestring, and multipolygon. In spatial SQL, each geometry value is associated with a spatial reference system (SRS). Each Spatial Reference System in the database is identified by a unique value of SRID. Therefore, before geometry can be produced and inserted into a table. The corresponding row of its SRID must exist in the SPATIAL_REFERENCE_SYSTEM table; otherwise construction of the geometry will fail. Further, when defining a table, a check constraint can be employed to enforce the rule that all geometries in a geometry column have the same SRID as that defined for the column in the GEOMETRY_COLUMNS table. 9

10 Currently, Internet has been changing the way of information access, sharing, and dissemination. It will further change the means of analysis and visualization of spatial data. there have been a number of different approaches implementing Web GIS such as plug-in which programs are downloaded into the browser environment; functions invoked from the browser are executed on the server via CGI, and Hybrid model where certain functions are executed on the server delivering a image file and an Application Programming Interface (API) delivers specific data to a client for local processing. Data Source Data used in this research are acquired from Idaho Falls Electric Power, which provides electric to residential and business areas in Idaho Falls areas. However, not all data employed in this study is accurate due to confidentiality agreements. The data were obtained on June 1, 2007 and were exported from ArcSDE to ArcGIS personal geodatabase (mdb), including many electric feature classes: substation transformers, transformers, switches, breakers, busbars, capacitors, fuses, primary lines, secondary lines, meters, poles, lights, secondary pedestal, service panel, secondary junction box, conduit information, splice, pull box, vault, sectionalizing vault, sectionalizing cabinet, meter cabinet, switch gear, traffic cabinet, anchor, crossarm, span guy, and also base maps such as highway, street, river, parcel and etc. The projected coordinate system was natively customized by using Transverse Mercator projected system, North American Datum 1983, and feet US unit. 10

11 Figure 4: an Example of Idaho Falls Electric Network Model including Electric Flow 11

12 Figure 5: Overview of Idaho Falls Base Map 12

13 Software Since this study copes with proprietary software, open source software and web application software, there are various applications to be utilized to accomplish this research such as ArcGIS Desktop 9.2, Microsoft Visual Studio 2005, MapServer 4.10, PostgreSQL 8.2.4/ PostGIS 1.3.1, Apache 2.2.4, PHP, JavaScript, HTML, Dynamic HTML, and Common Gateway Interface (CGI) Methodology Utility networks are built to provide the environment that accommodates energy, water, and communication. For example, water utility is gravity driven or pressurized depending on terrain surfaces, gas utility flow is driven by pressure in pipes, and flow in electric power utility is traveled from high voltage potential to low voltage. ArcGIS application provides a solution to create utility network via geometric network. The geometric network is a relationship model of connected edges (lines) and junctions (points) to represent behavior of network infrastructure in the real world. Commonly, geometric network consists of simple edge, complex edge, simple junction, and network junction. A simple edge and simple junction are to be represented as a single feature, complex edge to be simplified as a single feature that allows edges to connect without junction, and network junction, or orphan junction, to be used to maintain network integrity. When geometric network is constructed, logical network is also created correspondingly. This logical network has an important rule for geometric network since it is the connectivity table, which represents the relationships between features used for tracing and flow calculation. Logical network records how network elements are connected. So, for every junction in the network, the connectivity table lists the adjacent edges and connected junctions (figure 6). 13

14 Feature Class Feature ID Element ID Geometry Circuit c Circuit c Circuit c Secondary line Scl Edge Table Feature Class Feature ID Element ID Geometry Transformer Tr.2 2 Network Junction 1 1 Junction Table Junction Adjacent Junction and edge 1 10, , 13, 12 Connectivity table Figure 6: Connectivity Table in Logical Network Geometric network first need to be created and promote interested feature types (lines and points) to network feature types (edges or junctions). In this research, network feature types will be specified as simple edges and simple junctions since these types can provide the flow relationship among them (ESRI, 2007). Sources and sinks in a utility network are used in determining flow direction. Any junction feature class can take on the ancillary role of a source or a sink. A Substation Transformer will be identified as a source providing flow from, and meters will be stored as sinks giving where the flow will be terminated. Connectivity Rules will have an important rule when electric become complicated. It is used to logically constrain the type of electrical network features that may be connected to one another and the number of features of any particular type that can be connected to features of another electrical type by establishing these rules along with other rules (ESRI, 2007). For example, a transformer can be 14

15 connected from circuit to circuit or from circuit to secondary line. Meter can be attached by only a secondary line (figure 7). Figure 7: an Example of Connectivity Rule Interface in ArcGIS Desktop After setting connectivity rules properly, the electrical flow will be created via a Utility Network Analyst tool. If the result of flow is satisfied, the electric geometric network will be export to postgis by mandatory maintain the relationship between current element and previous element: parent element, and grandparent element. Current Element Parent Element Grandparent Element Connectivity table Figure 8: a Connectivity Table in Logical Network after Determining the Flow 15

16 Since, the relationship is in logical network (figure 8) which is hidden in the geometric network, the way to access is by using ArcObject. Figure 9: an Example of ArcObject Interface (ESRI, 2007) ArcObject is a framework behind ArcGIS application. It is a collection of platform-independent components (COMs) that provide service to support ArcGIS application. Component Object Model (COM) is a protocol connecting one ArcGIS software component with another which is assisted to access to a required object..net framework of Microsoft Visual Studio 2005 interacts with COM via COM wrapper classes to allow COM communicating with.net components. The algorithm of exporting from ArcGIS geometric network to PostGIS open source spatial database is illustrated in figure 10. The main interfaces of exporting geometric network are IGeometricNetwork, IUtilityNetwork, INetElementDescriptionEdit, INetworkFeature, IEdgeFeature, INetElements, ISimpleEdgeFeature, and ISimpleJunctionFeature. Also, a XML configuration file is used to express configuration of each feature class and fields to be exported into PostGIS by having mandatory fields: current element, parent element and geometry of each feature. Optional fields can be selected from existing fields of each feature class. In addition, this configuration file also provides a connection description and EPSG number; a numeric code is associated with coordinate system definitions (MapServer, 2007) 16

17 Read Geometric Network Read XML Configuration file Open & Close Database Check DB connection Connection fails Throw error exception Read each XML attribute Load Configuration Featrures to ExportCfg Object Export Network from Source Export Adjacent Feature Go to Next Feature Insert Features to Database Is Feature null? Throw error exception Export Feature Export Fields Export Feature Figure 10: Exporting from geometric Network to Open Source Spatial Database Algorithm Furthermore, this application uses the recursive approach to walk the network and export to PostGIS. To standardize from a custom projected coordinate system to standard projected coordinate system such as Universal Transverse Mercator (UTM) with easily match with the right EPSG number. For example, <EPSG: 26912> is a UTM zone 12, NAD 83, and Meter unit. ArcObject provides PCS number, which matches with EPSG number. C#.net code example IGeometry geometry; string geo = ""; ISpatialReferenceFactory srfactory = new SpatialReferenceEnvironmentClass(); IProjectedCoordinateSystem pcs = srfactory.createprojectedcoordinatesystem ((epsgnumber)); ISpatialReference sr = pcs; Since PostGIS requires geometry of each feature. IGeometry, IPoint, IPolyline, and IPointCollection in ArcObject assist developer to access to coordinates of each point 17

18 and each vertex in polyline. In addition, inserting each record in PostGIS tables requires PostgreSQL libraries to provide a complete.net functions to allow.net program to access a PostgreSQL database C#.net code example using System; using Npgsql; class Program { static void Main() { NpgsqlConnection conn = new NpgsqlConnection("Server= ;Port=5432;User Id=xxxxx;Password=xxxxx;Database=xxxxxxxxxx;"); conn.open(); Console.WriteLine("DB connected"); string SQL = "INSERT INTO SubstationXFMR values('1','9','str.9','- 1','7','SubstationXFMR','STR','1',GeometryFromText ('POINT( )',26912))"; NpgsqlCommand command = new NpgsqlCommand(SQL, conn); try { rowsaffected = command.executenonquery(); } finally { Console.WriteLine("It was added {0} lines in table ", rowsaffected); conn.close(); } } } Spatial Database is a relational database that allows storing large sets of binary large objects (BLOB) including location, shape, and dimension. Historically, database were not spatial enabled and could not directly store information about location and shape. Therefore, the spatial component was store separately from the main attribute database and using a reference present in both systems. This might cause inconsistent and desynchronized. Therefore, bringing the spatial information together with attribute information enable the database to provide its standard transaction support, integrity check, access control, indexing and other services. PostGIS is a spatial database that extends PostgreSQL, a free source powerful enterprise-level relational 18

19 database system (RDBMS) same as Oracle Spatial, DB2 Spatial, and Microsoft SQL server Spatial. This database allows storing several types of geographic data such as point, multipoint, line, multi line, polygon, and multipolygon and also including objects with location, shape and dimension. In addition, PostGIS has capabilities to manipulate and analysis geographic data directly in the database such as buffer, intersection, union, and etc. which produces this open source spatial database so powerful and reliable (Tyler 2005). PostGIS also follows Open Geospatial Consortium (OGC) standards which allow a wide variety of users to access data sets and management of their relations both geographic and alphanumeric data. Furthermore, if users access data across a network, storing data in the PostGIS database may be the best option because PostGIS processes your queries for data directly on the server, only the desired results are sent back over the network. With file-based data, more data has to be passed around, even before MapServer decides which pieces it needs. Server-side processing in a PostGIS database can significantly improve the performance of MapServer applications. Figure 11: pgadmin III Interface to Assist User to Access into PostgreSQL Database 19

20 To produce spatial database in PostGIS, there are two efficient methods: using pgadminiii, or psql internal command. pgadminiii has graphical user interface (GUI) that is easy to use and utilizes postgis template when creating spatial database (figure 11). Second, psql command is natively text-based interface to postgresql database. This approach processes faster than pgadminiii since the command processes line by line as SQL interpreter. Hence, producing spatial database in this research highlights on using psql command. There are two extra tables that support PostGIS system: geometry_columns, and spatial_ref_sys. geometry_columns table is used for keeping track of the geometry columns and their constraints, and spatial_ref_sys table is used for maintaining of the different spatial referencing systems that the geometry s coordinates are stored in. Then, PostGIS tables are created by using SQL command such as a fuse table. The addgeometrycolumn function is a new function added by PostGIS. This function adds a new column to the specified table and also adds a new row to the geometry_columns table in order for PostGIS system to maintain of it. BEGIN; CREATE TABLE fuse ( gid serial primary key, oid integer, currentid varchar(30), parentid varchar(30), phase integer, devicecode varchar(16), devicename varchar(16), enabled smallint); SELECT addgeometrycolumn('','fuse','geodata','26912','point',2); END; After tables created, data are inserted from exporting application to PostGIS. Then, spatial index needs to be created to speed up bounding-box based queries. This query is primarily employed to select the geometries within an area of interest, or within the display area of the map. It is important that the set of geometries can be selected rapidly since this is the most frequent query performed in web-based mapping. After 20

21 that, PostGIS has ability to update the database s cache of statistics and possibly reorganize the structure of some indexes to increase the speed of queries using those indexes. CREATE INDEX fuse_geodata_gist ON fuse USING gist(geodata); VACUUM; MapServer is an Open Source development environment for building spatially Internet-web applications developed at the University of Minnesota. MapServer is a map-rendering engine that works in a web environment as a CGI script or as standalone application via an API accessible from several programming languages such as PHP, Ruby, Java, C#, Python, and Perl (Bil, 2005). Mapserver also have advance cartographic output such as scale dependent feature drawing, map element automation (scale bar, reference map, and legend), thematic mapping using logical or regular expression-based classes, Map projection support, and a variety of raster and vector data formats support via OGR (Simple Feature Library) and OGL (Geospatial Data Abstraction Library) (Mapserver, 2007). Figure 12: Basic Operation of MapServer (Tyler 2005) 21

22 Usually, MapServer works behind a web server application. The web server received requests for maps and passes them to MapServer to creates the request map images from spatial information stored in digital format, both vector and raster data, and in spatial database such as PostGIS, Oracle Spatial, DB2 Spatial, and etc. and send back to the web server, which transmits it to the user (figure 12). Therefore, when a client submits a web request, hidden variables are passed via Common Gateway Interface (CGI), a protocol dealing with the information exchange between client and the server, to MapServer in the Web Server. After MapServer finished processing, it sends results including images and variables back to the client (figure 13). v.exe&map=/xxx/map_export.map&mode=map&layer=circuit Figure 13: an Example of a Map Image To produce map images through Internet via MapServer, map file will be created to specify the relationship between feature classes. So, MapServer can understand where data are located and define map characteristics to be drawn such as specify the connection type to postgis, specify layers, and specify classes in each layer. It also has a hierarchical structure such that some feature classes will fall under other feature classes. 22

23 Since the relationships between electric devices have been explored and stored in spatial database. The predicting outage devices can be determined by tracing upstream from customer meter location to the nearest secondary line and a transformer with a same phase, looking up all other secondary lines to the same transformer, then updating the database and flag possibly affected secondary lines and the transformer in the desired field, and finally displaying the update database with highlight by specifying the expression and highlight symbol in map file (figure 14). Figure 14: an Example of Predicted Outage Devices due to One Customer Furthermore, if there are numerous customers report the outages in a different transformer network. The predicted outage device can be determined by tracing upstream to the primary line, or circuit, and predict the upstream devices such as fuse, switch, or capacitor. 23

24 Result Since there are many steps to accomplish this study especially in process of creating a spatial database in PostGIS, creating a batch file is a practical approach because of the speed of executed line by line of psql internal command. In addition, pgadminiii also assists user to access to the open source spatial databases since this free application is user-friendly graphic approach and available after install postgresql database. Creating spatial database via pgadminiii should specify postgis template that will automatically produce spatial functions, objects and two extra tables containing spatial reference system and geometry columns. Spatial table can be created by using normal SQL command and need one extra spatial SQL command to pass geometry into geometry columns table and create constraint to the spatial object. Furthermore, exporting geometric network relationship to PostGIS open source spatial database by using recursive approach is a potential approach since the function calls itself until no any feature passed. Then, the function is terminated. XML configuration file is used to pass the significant information and set up the feature classes and fields to be exported before exporting application started. After the relationship exported, there are many open source application that can connect to PostGIS spatial database and display it, such as udig, Quantum GIS, and MapServer. However, only MapServer has ability to read PostGIS spatial database and display via Web GIS. Further, MapServer requires a map configuration file to define the content of each feature class to be drawn, point to where data are located, and define how feature objects to be drawn. Also, to produce dynamic Web GIS, variables such as mapsize, zoom, cellsize and extent can pass to MapServer via CGI and using JavaScript can pass some variables and do some easy calculation such as measurement on client side. In addition, determining predicted outage devices by 24

25 using SQL command via server is a potential approach since the database has ability to retrieve and update the required data faster than searching via sequential file. Conclusion The abilities of open source application are potentially powerful; both open source spatial database and open source web GIS applications are able to archive almost everything that most expensive commercial application can do but do not cost anything except an intern s work. Also, the open source spatial database can be created by imported from proprietary format such as ArcGIS personal geodatabase (mdb) and the capabilities of open source application such as MapServer, PHP, and Javascript can be used to display spatial features and analysis results via dynamic web GIS. Furthermore, the open source applications can provide open development environments to implement use specific analysis function. Future Works Since, an open source spatial database has ability to apply SQL spatial analysis functions. It is possible to apply these functions to determine the relationships of utility network. This will expand the ability of open source application and avoid using proprietary software. Also, open source applications and open source database have capabilities to produce potentially dynamic web GIS such as presenting the direction of electric flow via MapServer, or using SQL spatial functions to analysis required data. Further, the process of exporting from proprietary software to open spatial database takes a lot of times. There should have the possibility to optimize this application to enhance the performance. 25

26 Reference Tyler Mitchell Web Mapping Illustrated. O Reilly Publisher Bil Kropla Beginning MapServer: Open Source GIS Development. Apress Publisher Robert Burke Getting to Know ArcObjects. ESRI Press Publisher Kang-Tsung Chang Programming ArcObjects with VBA, A Task-Oriented Approach. CRC Press Publisher Karli Watson, Christian Nagel, Jacob Hammer Pederson, Jon D. Reid, Morgan Skinner, and Eric White Beginning Visual C# Wrox Publisher. Korry Douglas, Susan Douglas PostgreSQL: A comprehensive guide to building, programming, and asminsitratering PostgreSQL databases. Sams Publisher Menno-Jan Kraak. 2004, The role of the map in a Web-GIS environment. Journal of Geographical Systems. Publisher Springer Berlin/Heidelberg Volume 6 Number 2 June, Pages Ranga RaJu Vatsavai, Shashi Shekhar, Thomas E. Burk, and Stephen Lime UMN-MapServer: A High-Performance, Interoperable, and Open Source Web Mapping and Geo-Spatial Analysis System. Geographic, Information Science Book Series Lecture Notes in Computer Science. Publisher Springer Berlin / Heidelberg volume 4197/2006: Pages Bo Huang and Hui Lin Design of a Query Language for Accessing Spatial Analysis in the Web Environment. Journal GeoInformatica Publisher Springer Netherlands volume 3, Number 2 / June, 1999 Pages Hui Lin, and Bo Huang SQL/SDA: a query language for supporting spatial data analysis and its Web-based implementation. Knowledge and Data Engineering, Volume 13, Issue 4, July-Aug. Page(s):

27 Zhong R Pend, and Chuanrong Zhang The roles of geography markup language (GML), scalable vector graphics (SVG), and Web feature service (WFS) specifications in the development of Internet geographic information systems (GIS). Journal of Geographical Systems Volume 6, Number 2 / June, Pages Zhong R Peng, and Ming H Tsou Internet GIS: Distributed Geographic Information Services for the Internet and Wireless Networks. Wiley & Sons Press. Shashi Shekhar, and Sanjay Chawla Spatial Databases: A Tour. Prentice Hall Press VDS Technologies MapServer. PostGIS. PostgreSQL. GDAL Geospatial Data Abstraction Library. OGR Simple Feature Library. ArcGIS Desktop Help overview.htm Quantum GIS. User-Friendly Desktop Internet GIS (udig) 27

28 Appendix 28

29 Utilized ArcObject Component Object Models ISpatialReferenceFactory Interface ISpatialReference Interface IProjectedCoordinateSystem Interface IPoint Interface IPointCollection Interface IGxDialog Interface IGxObjectFilter Interface IEnumGxObject Interface ITrackCancel Interface IProgressDialogFactory Interface IProgressDialog2 Interface esrielementtype Constant esrifeaturetype Constant IRow Interface IFeatureClassContainer Interface IFeatureDataset Interface IDataset Interface IFeatureWorkspace Interface IFeatureSelection Interface IFeatureClass Interface IFeatureCursor Interface IFeature Interface ILayerFile Interface ILayer Interface ISelectionSet Interface IQueryFilter Interface IGeometricNetwork Interface IUtilityNetwork Interface INetElementDescriptionEdit Interface INetworkFeature Interface IEdgeFeature Interface INetElements Interface ISimpleEdgeFeature Interface ISimpleJunctionFeature Interface 29