ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001 
47 
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2.2 CITY TERRAIN MODLE 
The city terrain is needed to show 3D city scene. Comparing to 
building model, the required of city terrain model is simple. In 
order to improve the efficiency in 3D visualization city on 
Internet, we select the GRID model that is a kind of DEM model 
to construct the city terrain. 
To visualization the GRID model, we divide the quadrangle into 
two triangles. Figure 2 shows the city terrain with the GRID 
model. 
Fig. 2: GRID Model 
3. THE SYSTEM ARCHITERCTURE AND STORING LARGE 
DATE SET 
The system architecture has been designed to implement 
visualization the 3D city data on Internet. For visualization the 
Web 3D data, some researchers (Lindenbeck, 1998,Siyka 
Zlatanova, 1999) have presented the client-server architecture. 
The client-server architecture is proved to be stable for Internet 
communication. Compare to the approach presented in (Coors, 
1998), our approach uses 3D GIS Applet to visualize and 
interact with data. The approach can also manipulate and 
query respectively on the server and client station. In order to 
efficiently manage large 3D building data in database at 
server-side and query the building attribute data from the 
client-side, the R-tree structure is proved to be a useful index 
(Gruber, 1998). According to the LC model and R-tree index in 
database, the way to query the attribute data of building is 
presented. 
3.1 The system architecture 
The system architecture for visualization and query on Internet, 
presented here, is typical client-server architecture. (See 
Figure 3) In this architecture, the city buildings attribute data 
are stored on the server(s) database. The process of 
client-server communication can be described shortly as 
follows: The client-side downloads a 3D GIS Applet from the 
server-side by Web browser. This Applet runs on client-side to 
show the 3D scene and communicate with the server. Some 
behaviors have been implemented at client-side. Using these 
behaviors, the user can walk through the 3D scene by mouse 
or navigate the 3D scene by keyboard. Especially, they can 
designate the flying route from a 2D map to fly over the 3D 
scene. The building at the 3D scene can be picked and get the 
building- ID which identifies the building. The 3D GIS Applet 
sends the building-ID to the Web server and the server can 
return the building attribute data to the client-side. With this 
process, the building attribute can be queried at client-side.