device. When adjusted, the positions of the stereoscopic
points indicate the positions of stereo conjugate points in
the stereoscopic images. Photo 3 is one example. In this
case, 25 stereo conjugate points are determined manually
using the 3D display module and are then provided to the
computer.
Photo 3 Manually determined stereo conjugate points
In another case, it is also possible to identify stereo
conjugate lines instead of stereo conjugate points. Photo
4 is one example of this case. These lines are drawn one
by one along surfaces such as valleys and ridges, with a
mouse looking at the stereoscopic model through liquid
crystal shutter glasses. The steps for drawing these lines
are as follow.
1)First draw one line of a stereopair along a valley or a
ridge on one (left or right) image.
2)Next draw the second line in exactly the same
position on the other image.
3)Repeat these two steps.
These lines are very useful for automatic stereo matching
because the accuracy of stereo matching is usually bad
where valleys and ridges, when an image correlation
method is used.
Photo 4 Manually drawn stereopair lines
3.2 Correcting errors of stereo matching
After the stereo matching, the errors of automatically
determined stereo conjugate points can be corrected by
using the man— machine interface easily. Photo 5 is a
simultaneous display of stereoscopic images and stereo
conjugate points determined automatically. When the
stereoscopic model from the stereoscopic images is
observed, correct points are positioned on the surface of
the model and error points are above or below the true
surface. These error points can be corrected easily by the
mouse, and a precise DEM can be extracted after these
corrections.
Photo 5 Simultaneous display of stereoscopic images and stereo conjugate points
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
4.1
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