ISPRS, Vol.34, Part 2W2, ‘'Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
328 
Figure5. Path Terrain Quick Scanning 
Besides, the altitude of path can be adjusted to observe the 
terrain effect at different heights. This is important when the 
inter-visibility conduct is needed in case of communication 
device layout, or foresting by airplane, or fine farming 
investigation. In some complicated situation, when the satellite 
line-of-sight is cut off and the number of navigation satellites are 
reduced, GPS navigation will become a problem and this will be 
dangerous for flight. It is quite essential to indicate this 
information for related parts of path on DEM. 
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Figure6. Path Evaluation And Information Indication 
Under this circumstance, the terrain induced environmental 
influence on GPS positioning is also studied and is indicated on 
a right windowed column for user reference. The window also 
includes navigation accuracy by GPS. The satellite cut off by 
terrain is denoted with a red color line. Zooming is provided to 
show regional parts of the path in complicated terrain situation. 3 
levels of zooming is supported by the system. 
5. GPS NAVIGATION PREDICTION 
In some situation, it is useful to know the availability of GPS 
ahead of a specified time span at an appointed place. In this 
software system, the terrain induced visibility of GPS is taken 
into consideration. GPS satellite predicted positions in the sky 
are calculated from almanacs files. The position plus terrain 
factors determine the predicted GPS visibility and possible 
positioning accuracy( DOP values). 
6. CONCLUSION AND FUTURE PLAN 
The software system is an integrated analysis tool for path 
planning and investigation by GPS navigation. 
Figure7. Predicted Satellite Visibility Sky Plot 
Figure8. Predicted Positioning DOP Curve 
Function of DEM generation from other data source such as RS, 
electronic DTM map is to be included in. rapid compression 
algorithm for DEM or DTM generation is still to be discussed 
to speed up the whole system. 
ACKNOWLEDGEMENTS: 
The first author of the paper would like to thank Professor Du 
Qinyun, ,Dr. Wenpin Jiang, Dr. Su Kang and Dr. Yan Li for their 
support for the project. Part of the research has been supported 
by National Science and Technology Foundation for Surveying 
and Mapping under contract number 99011. The research is also 
supported by the cooperation project from China General 
Company Of Aviation And Aeronautics. 
REFERENCE: 
[1] . Li Deren, Zhong Sidong, Guo Bingxuan, Road Network 
Generation by Mean of 3S and multi-sense. 3rd International 
workshop on urban 3d multimedia mapping, Section D. Monitor 
road transportation and application, 2000, pp23-30. 
[2] . Li Deren, Chen Xiaoming, Guo Bingxuan, Zhong Sidong, 
Road network generation by mean of GPS/GIS Integration, 
International workshop on Geographic Information systems for 
transport (GIS/T) and Intelligent Transport System (ITS), 1999 
[3] . David Tyler, Integration of a GPS DTM into an Agricultural 
GIS, University of Maine, ION-GPS1992 
[4] . R.Clark, R.Lee, A Comparison of Rapid GPS Techniques for 
Development of Topographic Maps for Precision Farming, 
University of Georgia, ION-GPS 1996, pp495-504 
[5] Li Zhilin, Zhu Qing, Didital Elevation Model, WTUSM Press, 
2000.3 
[6] TANG Guoan, A Research on the Accuracy of Digital 
Elevation Models,SCIENCE PRESS, Beijing New York2000 
BIOGRAPGY 
Linyuan xia: Associate Prof., Graduated from Wuhan Technical 
University of Surveying and Mapping in 1986(Geodesy). 
Research field: GPS and related application.