Research Of The Lightweight WebGIS Based On SVG

Based on a SVG prototype system ,this papaer intends to provide a lightweight WebGIS solution.In reference of OGC's simple object model,this paper use the design method of the object-oriented to construction of the SVG-based object model. To avoid the "impedance mismatch" contradictions between the traditional GIS's object-oriented data model and the relational database 's relational model, this paper use the object-oriented database DB4O as the Data Server 's data buffer.Using the client scripting language JavaScript to call the SVG DOM interface, this paper realizes the basic functions of the WebGIS ,such as Zoom in and Out , Pan ,Query the attributes and Measure.For these basic functions are realized in the client,so the speed of the user and the system interactive is quick and the server burden is lighter. Comparing the WebGIS of the "Server strategy" ,this paper overcomes the general shortage of the speed of response is restrained by network bandwidth and the heavy burden on the server.Using the Ajax asynchronous refurbishing mechanism, this paper may load data dynamicly and selectively, which avoids the data that loads does not need ,saves the network band width and overcomes the general SVG application systems'sshortcoming of long time cost for loading data.Moreover, the analysis function is also based on the Ajax asynchronous refurbishing mechanism. The user uses XMLHttpRequest to send analysis request to the server.The server receives the request ,resolves it and return the data to the client. Throught the JavaScript ,the Client analysis the return result and refurbishes the part of the map that has changed.This solution avoids to download all data again and makes the Web application like the desktip application.Based on the lightweight structure of JavaEE, this paper uses MVC model to achieve the separation of logic and performance,it takes Java Servlet as controller to the MVC. GIS application server takes JTS(Java Topology Suite)as the lower resolving of the geometric topology relation ,it has realized the buffer analysis and two kinds spatial query.For this ,this paper overcomes the shortcoming of lacking the functions of the saptial analysi to the general SVG system and improves the SVG' ability to solve the complex question.This paper's prototype system is based on open source or the free technology (DB4O, JTS, TomCat are open source products, Java is a free product). Based on open source or the free technology, not only the system construction's software cost is quite inexpensive, moreover system's maintenance and the expansion have the very good guarantee, and it will not be restrained with some factory.The research indicated that SVG has the ability to construct lightweight WebGIS having the efficient functions with JTS , DB4O and lightweight JavaEE and SVG WebGIS is a good solution for lightweight Web System.