CMRT09: Object Extraction for 3D City Models, Road Databases and Traffic Monitoring - Concepts, Algorithms, and Evaluation 
4. 3D SCENES RENDERING 
For a given location, the server gets the surrounding DEM, 
models data and other additional information from web map 
data server. In our approach, only those tiles which lie in 
frustum view region will be loaded, and search those tiles are 
by grid index (see figure 4a). If viewpoint moves over an 
adjacent tile the algorithm will tend to maintain a square of tiles 
centered on this new tile (which will be load in client memory 
new and becomes the current tiles). At the same time, the 
algorithm will remove some far tiles which are not within the 
field-of-view in order to free memory for the fetching of new 
tiles (see figure 4b). As figure 3a indicated, most of the memory 
of mobile device was consumed at the step. Note that the 
algorithm implicitly handles the case where viewpoint jumps to 
a new tile that is not adjacent to the current one. The quad-tree 
representation of tile data enables very fast view frustum 
culling. 
Figure4. Tiles management and adaptive loading 
a) . A square area centered on the viewpoint. 
b) .Square area preservation on viewpoint move 
In order to enhance rendering efficiency, numerous methods for 
mesh simplification have been developed on the last decade. In 
this paper, the simplifying approach is based on the terrain 
height field and terrains are represented in various resolution 
meshes. Firstly, the full terrain height-field is divided into 
regular tiles, and then the appropriate level of detail is 
computed and generated dynamically, allowing for smooth 
changes of resolution across area of the surface (see figure 5), 
those even areas are represented in low resolution meshes and 
the uneven areas are represented in high resolution meshes. 
Fig5. Simplified mesh based on terrain height fields 
5. CLIENT-SERVER ARCHITECTURE FOR 3D 
NAVIGATION 
There are stand alone 3D applications which can now run on 
mobile devices. However, for the limited capabilities of the 
mobile devices and aiming to provide the users a panorama 
scene that fits with the real surroundings navigation, our 
approach is implemented based on client-server architecture 
(see figure 6). 
Figure6. Client-server architecture of 3D mobile navigation 
system 
The server system provides a web service interface to the 
virtual environment, and it is responsible for handling requests 
sent from the clients. The 3D models’ datasets are hosted on a 
web map data server, and the server interprets and controls 
navigation commands, then sends the requests to a web 3D 
rendering server to generate a virtual panorama by rendering 
the DEM and a web navigation server generates 3D scenes 
using the panorama images and some other nodes 
corresponding to meta information. The rendering component 
encodes the frames into video stream as 3D scene files. The 
clients can communicate with the server by exchanging SOAP 
messages and the 3D scene files are finally sent to a mobile 
client to show. 
A mobile device as a thin client system need not contain any 
application of navigation software, it only needs capabilities for 
receiving and playing the multimedia, capturing the user 
requests, sending and receiving SOAP message. 
6. EXPERMENT AND CONCLUSIONS 
Due to the complexity of the real world scenario and the vast 
computational power required to achieve a usable performance, 
navigation in 3D environment is still a tough task. In our 
experiment, we handle complex 3D scene models by culling 
areas outside of the field of view, and by using multi-resolution 
models to reduce the data. 
6.1 Experiment and results 
This paper proposed an efficient framework for resource 
management and texture handing regarding online and offline 
procession. The Pc server’s primary configurations are shown 
in table 1, and the client platform we selected was a WindowCE 
device as for its multimedia capability and easy of 
programming with Embedded C++. 
CPU 
Pentium(R) 5, 2. 66GHz 
GPU 
ATI MOBILTY RANEON, 7500 
Memory 
1.00GB 
Storage 
250GB 
Operating System 
WinXp, Professional, SP2 
Table 1. Configurations of Pc Server 
In the experiment to test the efficiency of network transmission, 
we found the major bottleneck is the massive 3D models’