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Data Processing, Algorithm and Modelling
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Automated DEM generation from SPOT imagery
Experiment
We use a pair of SPOT images of Hong Kong to test our DEM generating program (figure 4). The left image
is received on October 1, 1996. Its orientation angle is 11 degree and incidence angle is 30 degree. The right
image is received on January 2, 1996. Its orientation angle is 8.8 degree and incidence angle is 13.8 degree
.
Firstly, we use 20 tie points to refine the sensor model previously developed at the Center for Remote
Imaging, Sensing and Processing. The method described in this paper is used to generate the DEM
automatically. The generated DEM is shown figure 5.
In order to assess the accuracy of the DEM, we use 126 tie points manually selected to check its accuracy.
We compare the altitude of the DEM with the altitude calculated with tie points. The altitude disparity of each
point is shown in figure 7. The altitude standard deviation is 19.27 meters. The mean deviation is 0.53
meters and the absolute mean deviation is 16.15 meters.
Figure 5, A stereo pair of SPOT images over Hong Kong © 1996 CNES.Figure 6, DEM generated from the stereo pair in Figure 5.
Conclusion
We have presented a fully automated method of DEM generation from SPOT imagery. From the experiment
result and the accuracy assessment, it is apparent that in terms of geometric accuracy the new method
produces an acceptable result for topographic mapping. However, in many areas, especially in the area
where terrain features are rare, there is still much noise caused by false matching. Thus the altitude
accuracy of the DEM still needs improvement in those areas.
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