ra- 
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' Institute of Surveying and Mapping, Information Engineering University, No.66, Longhai Road, Zhengzhou, 
R.P.China 
b . 
KEY WORDS: Navigation assistant, Mobile devices, Pyramid model, Quad-tree structure, Multi-resolution 
ABSTRACT: 
Traditional navigation visualization utilizes two-dimensional digital maps for road guidance, and with the advances in visualization 
technique, algorithms, and computer hardware, it offer an opportunity of applications for mobile users in 3D virtual environment. 
The main challenge comes from how to efficiently provide up-to-data location-specific data and navigation services. For the real 3D 
world usually contains a lot of details and represents a huge amount of datasets, so it is a difficult to visualize the complex virtual 3D 
scenes and navigate in them on mobile devices. To solve the problem, this paper proposed a novel approach that is based on 
geographic web services and the servers dynamically generate the 3D scenes in terms of the navigation commands and then send the 
resulting as video-encoded image stream to the mobile client. In order to enhance the efficiency of 3D scenes rendering, those virtual 
3D models’ datasets were prepared and organized in an offline process. The approach allows us to provide interactivity for complex 
virtual 3D scenes on resource and bandwidth limited mobile devices. 
1. INTRODUCTION 
Traditional navigation and trip planning is two-dimensional 
map display mode, and user can only accept limited information 
organization, poor presentation, and lack of interaction. On the 
contrary, applying 3D techniques for realistic visualizations into 
navigation fields provides new or better solutions that are 
hardly solved by 2D means, the advantages over 2D case are as 
follows: 1) easy navigation of the information space allowing 
better user interaction with the virtual objects and user can 
understand the displayed data through the existence of visual 
metaphors better. In contrast, 2D map reading is a skill which 
requires specific training; 2) the capability to display more data 
at one time, because each location on a 2D map is shown in the 
same scale, and users need to change scales in order to switch 
from viewing local details to overviews. The perspective view, 
on the other hand, has the inherent capability of combining 
different scales into one scene by dedicating a larger amount of 
the screen to the immediate surrounding while at the same time 
showing the entire route in an overview. 
Mobile devices, like personal digital assistants (PDAs), mobile 
phones, Palm Pilots, or Pocket PCs, have made undreamed 
progress in computing power, function of displaying and input 
options a few years ago. Combined with a Global Positioning 
System (GPS) receiver, the mobile devices offers an 
opportunity to interact with a map display showing the current 
location and orientation. 
Therefore, focused on how to represent 3D environment which 
support navigation on mobile devices, this paper presents a 
client-server solution for accessing virtual 3D scenes for 
navigation. The approach is based on 3D modelling techniques 
in which a full 3D model is generated on sever and sends the 
resulting as video-encoded image stream to the mobile client. 
The solution can be decomposed in three steps. The first one is 
pre-processing. The main purpose is preparing data offline. The 
second one is 3D scenes rendering. The user controls the client 
by navigation command sketches drawn directly on the view- 
plane and the sketches are sent to the server, then the server 
interprets these sketches in terms of navigation commands, and 
generates the 3D panorama scenes. The last one is sends the 
results as image sequences to the mobile client. 
2. RELATED WORKS 
Mobile applications of virtual 3D scenes represent a major and 
complex research challenge and bottlenecks due to limited 
bandwidth and graphic capabilities, restricted interaction 
capabilities, data standardizations and distribution techniques, 
and digital rights issues. The main challenge here is how to 
render the 3D scenes and models as to usable navigation task 
within the 3D environment because there lack of an efficient 3D 
engine and suitable 3D model that would allow such 
development and field experiments. And the other challenge for 
the navigation domain comes from how to maintain real-time 
update rates in loading and unloading large, complex datasets. 
In fact, 3D space data obtain from the natural environment is 
Institute of Surveying and Mapping, Information Engineering University, No.66, Longhai Road, Zhengzhou, R.P.China. 450052. 
E-mail: chxy_wenjiang37@yahoo.cn; kissfro9642@sina.com. Tel: 86-13017690807.