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3D Terrain visualization for Web GIS
4. Prototype design and implementation
A prototype application, Singapore Terrain Explorer (STE), is designed to serve as a testbed for the abovementioned visualization method. Six main components are involved: 3D scene, local map viewer, world map viewer, coordinates display, information board and query pad.  Figure 5: Prototype design of STE The prototype implementation is on the basis of the integration of Java applet and VRML browser. Apache Web server is adopted. Java Database Connection (JDBC) acts as the interface to retrieve all geo-related information from the database. The communications between different VRML components such as the 3D scene and the local map view is done by embedded Script node in VRML. Other 2D components, i.e. the coordinate display, the information board, the Singapore map view and the query pad, are connected with the VRML components by EAI. If using Java scripts in Script node, information can be exchanged between scripts and EAI programs. Both of them have JDBC connection with geo-database. As a prototype, we simplify other geo-information as a table of names of the place of interest, important architectures, and subway stations. Figure 5 illustrates the prototype design of STE, especially the relationships among the six components in terms of implementation. In the 3D scene, users can interactively explore the geographical information by flying through/walking on the terrain surface and switch on/off different layers of theme data. A further click on a specific object may link to a new HTML page describing the geographical details at this location. The local map viewer is a floating 2D panel over the 3D scene, which contains a map of current terrain tile with a marker to point out the position and orientation of the viewpoint in the virtual world. The world map viewer tracks the current viewpoint too, but the main use is to present the global view of all terrain tiles. It also offers the short cut to quickly move to another location by simply clicking on the desired place on the map. The coordinates display shows the longitude/latitude coordinates values of current viewpoint position to help users to have a position reference about the environment. The information board is used to present local geographical information related to the current tile. With the view area changing, the contents on board are updated as well. The query pad gives users the opportunity to textually enquire about specific information from the database, such as asking for information about a place of interest. The layout of interface design is displayed in Figure 6.  Figure 6: Layout of prototype interface design |