I am trying to use ILWIS 3.7.2 to digitize contour lines with the Stereo Pair Anaglyph Viewer. I am using scanned aerial photos from the 1940s and 50s.
For some reason the right image always appears slightly rotated, which prevents me from seeing relief. I have created several epipolar stereo pairs from different images and I keep having the same problem. Last time I posted to this forum someone suggested I use a different program called Stereophotomaker. This program works, but it doesn't have a pixel shift option that can be used to digitize contours. I followed the directions in the Help section on how to create a stereo pair in ILWIS and I believe that I am entering everything correctly. Has anyone else experienced this problem before? Any suggestions on how to correct this? Below are two screenshots the first is an anaglyph created using Stereophotomaker (it shows relief when viewed with Red/Blue glasses and is essentially what I am trying to make in ILWIS so I can digitize). The other is what I get in ILWIS, note that roads in the right image (blue) do not line up with the left at all:
The photos are not an epipolar stereopair, therefore the anaglyph does
not show correctly.
Can you please inform me which are the steps that you followed to create
an epipolar stereopair?
- Select and digitize two, three or four fiducial marks in each photo.
- Choose fiducial marks that are opposite each other, so that the
Principal Point appears approximately in the center of the photo.
- Fiducial marks are the circles that you see near the border of aerial
photographs, in the corners and in the middle of the edges.
- The Principal Point of each photo is automatically computed. Find this
point in the other photo, and digitize it as "Transferred Principal Point".
- If there is any scale difference in the photos (airplane was not
flying horizontally or was flying at a different height), also digitize
the scaling points.
This should compute a correct epipolar stereopair.