Spatial Data Interoperability Based On GML And Web Service

The 21st century is not only an information era, but a network era. The function ofGeographic Information System (GIS) is being converted from providing access to specialspatial data for single user to making use of computer network spreading all over theworld to provide inter-current on-line spatial data service for multi-users.Along with issuing the conception of National Spatial Data Infrastructure (NSDI) andDigital Earth, open geographic information network is gradually developing on the basisof world-extended geographic coordinates and their interrelation and on the basicinformation platform of network. Spatial Data become sharing resources and span thelimitation of time and space. Geographic information is becoming an important part ofnational or world information flow and one of most basic information service in thepresent society.Information sharing has become an important mark of the development of moderninformation society. Spatial data interoperability is the certain result of informationsharing and will become an important part in the research field of the 21st centuryGeographic Information System (GIS).In China, information sharing has been facing many questions. In the past years, largeamounts of money and energy have been spent to collect some kinds of resources data onunderground, ground and atmosphere. But because of difference of data contents andsources, difference of spatial data model and difference of GIS software platforms, theextent of information sharing is not high. Information resources can't be utilized mutually.These result to the so-called information island.The problem on the geographic information sharing, interoperability and integration needsto be always solved on the development of Geographic Information System (GIS) in therecent years. It becomes very important how to make different Geographic InformationSystem (GIS) software acquire, integrate and analyze quickly data from different sources,how to interoperate these integrated data in the different system, how to acquire data fromthe heterostructue distributed database.At present, WebGIS is designed for special GIS data and application. So it is verydifferent to use WebGIS to interoperate hetero-structure spatial data andplatform-spanning operate.In the recent 20 years, the development of computer technology and the enlargement ofapplication field drove the development of Geographic Information System (GIS).Especially, the development of computer technology has become main power of the rapiddevelopment of technology of Geographic Information System (GIS). XML and WebService are the computer technology based on network in the recent years.XML is an efficient tool of solution to the above problem. OpenGIS consortium appliedXML to the field of spatial information and issued Geography Markup Language (GML),the solution to the modeling, transport and storage of geographic data.WebGIS system based on Web Service may interoperate between different GIS platformsor between GIS system and the other system because Web Service solves the integrationproblem of multi-sources hetero-structure spatial data.GML and Web Service based on XML solve spatial data sharing, interoperability andintegration.First, the thesis discussed GML and core technology, Web Service technology and OGCinteroperability protocols. Second, three data layers in the Liaoning province fundamentalgeographic information database at the scale of 1:250000 were acted as experimentaldata. .Net of Microsoft and MapObjects of ESRI were used. The publication of spatialdata was implemented based on GML and Web Service and solve the problem of sharingand interoperability of multi-sources hetero-structure spatial data that traditional WebGIScould not solve. This system consisted of three parts, spatial database, Web service ofspatial data publication and visulization of spatial data. The main problems being solvedincluded:--Convert spatial data from internal format into GML format. First, GML profile wasbuilt. Second, application schema was built. At last, GML format of spatial data was built.In the paper, three layers (boundary, railway and resident) in the spatial database wereconverted into GML format. The key of conversion was interpretation of spatial datatypes.--Convert spatial data from GML format into SVG format and implementation of graphicinteractive function based on SVG Client. Virtually, the conversion from GML to SVGwas the conversion from one kind of XML format to another kind of XML format. Theconversion was realized through XSLT. Though SVG had strong graphic interactivefunction and meet the need of simple graphic operation, its function was not enough interms of map display and operation. The function development was needed. JavaScriptwas used in the function development.--Make use of GML and Web Service to publish spatial data to realize spatial data sharingand interoperability. The current GIS systems were mainly based on two platforms, J2EEand Microsoft from the view of technicial implementation. Java and .Net have supportedwell to the Web Service, for example, accessing WSDL document automatically, creatingclient code of Web Service. At the same time, these two platforms packed request andparameters into the SOAP information, sent to the Web Service and converted the returnedSOAP information into usable object. This design used Arc/Info8.3 as managementplatform, stored spatial data into relational database Oracle9i and managed data throughspatial data engine ArcSDE8.3. In the .Net development environment, the functionmodule of Mapobjects was re-packed. Spatial data and attribute data were accessed andconverted into GML format. In the end, spatial data were published via Web Service. Thusspatial data sharing and interoperability were realized.This paper only built a publication instance of spatial data based on GML and WebService. Many questions should be researched deeply, for example, GML database,visualization of three dimension spatial data via Internet, spatial data safety on Internet.