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# Full text

Title
The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics
Author
Chen, Jun

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