ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001 
Figure 2. Source Data Processing 
Figure 3. Sketch DEM 
Figure 3 shows the regional sketch of DEM after source data 
decoding preparation. 
3. PATH GENERATION AND REPRESENTATION 
~x 
~w 
Y 
= 
w 
Z 
DEM 
vz 
where 
R is rotation matrix, £ x ,£ y ,£ z are rotation angles, 
VJf,VF,VZ are origin displacement between the two 
coordinate systems, k is scale difference for two systems. 
These transform parameters are determined from a number of 
known coordinate points in both systems. When rotation and 
scale can be ignored, transform become a simple displacing by 
origin offset of two coordinate systems. 
Another coordinate modification is projection from 3D to 2D 
plane. Mercator projection or Gauss(Gauss-Kruger) projection 
is the frequently used model to achieve this. When the projection 
is performed before, coordinate transform is carried out on a 
specified plane. This will be a 2D coordinate transform. Above 
Wolf-Bursa model is reduced into a 2D model. 
Path generated from transformed point data is indicated on DEM 
map with a red color curve. 
Figure4. Path Indication On DEM Map 
To facilitate flexible analysis, Path to be displayed on DEM can 
be generated in two ways: 
(1) Virtual path selection by mouse on DEM displayed. In this 
case, the chosen path can be stored as a file and can be 
recalled for later analysis. 
(2) Path generation from navigated files. 
In case(2), the path is an actual traveled or flight path. The point 
position accuracy on path depends on GPS positioning mode. If 
single point positioning mode is used, the spatial accuracy is 
+/-30m(with SA off). If navigation is in DGPS mode, the point 
accuracy will be +/-2m to +/-5m. 
After positioning, point coordinates must be transformed from 
navigation system(WGS-84) to DEM based coordinate system. 
The general transform principle can be expressed by following 
Wolf-Bursa model: 
4. PATH ANALYSIS AND EVALUATION 
After a path is generated and displayed on the DEM, it. can be 
analyzed and evaluated from the following aspects: 
(1) Quick terrain environmental scanning. 
(2) Path terrain display at different altitudes. 
(3) GPS satellite direction indication or interruption denoting on 
DEM. 
(4) Local terrain zooming at interest parts of the path. 
(5) Navigate positioning accuracy indication and terrain 
multipath influence indication. 
First, if you want to have a scanning along the generated path so 
that a clear understanding of the rough terrain backgrounds can 
be obtained, you can chose the quick moving function from the 
menu. 
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