Topic: correct entry of camera calibration information with aerial photos
Ok, firstly let me set the scene...
I have a SPOT5 orthoimage (created using COSI-Corr), which I used (along with SRTM topo data) to provide reference information when I extracted a stereo DEM using PCI's Orthoengine module for 3 overlapping aerial photos. However, whenever I included the camera distortion information, the correlation failed in the corners of each image during the DEM extraction. This made me think there might be a problem with the camera distortion info I entered. Anyhow, I extracted a good stereo dem without the distortion info. I used this stereo DEM, along with the original SPOT5 orthoimage to orthorectictify one of the stereo aerial photos in COSI-Corr (including the camera distortion information this time). I then used this ortho aerial photo and stereo DEM to orthorectify one of the other overlapping aerial photos, taken from the same time. Why? Because I wanted to check there was no deformation signal between the two aerial photos - and if there was, to try to identify why and where it comes from. Anyway, during Correlation I did get a strange looking deformation signal (which only broadly correlates with topography), with deformation signals of between -2 m and 2 m. Significant, considering there should be no deformation at all! Therefore, there is a problem somewhere with the orthorectification of the aerial photos. Because the stereo DEM I am using looks good, I am not sure this is the cause of the problem (it might be adding to it, since it was created without distortion info)? However, I am suspicious of the camera calibration info, which caused the stereo DEM extraction to fail in the corners. Therefore I was thinking maybe I am entering this information incorrectly in COSI-Corr, and this is what is causing this strange deformation signal? Phew... sorry that took so long to explain.
So now for my current problem!:
... so I suspect I am entering the camera calibration information incorrectly in COSI-Corr. I went back to check carefully how to enter this info... any I have some questions!
So the raw aerial photos arrive in .tif format, and look like the following image:
I rotate these by -90° to give the following image, because it is easier to work with the image when the top = N, left = W, right = E, bottom = S:
However, the Calibration Report gives info for this image "upside down" to the image I have. For example (note x increases to the right, and y increases down):
So my question is: when entering the calibration info for my aerial photo, do I simply rotate the info above, or do I mirror it? For example:
rotated 180° =
It must be important which one I do. In the mirrored version, the xy is the same as cosi-corr (i.e. x increases to the right, and y increases up); therefore, the sign convention of the PPA doesn't need to be changed. Also, the fiducial measurements for the left and right sides of the image will be opposite to the 180° rotated version.
Finally, if the 180° version is correct, does this rotation affect the radial distortions. In other words, do I need to change the sign for the radial distortions? Will mirroring the image also affect these distortions? In COSI-Corr I enter this distortion info as "radial distance" in mm (e.g. 20) and distortion in um (so for the 20 mm example, the distortion would be -5 um) - is this correct? Here's the radial distortion table for the 1982 images:
Of course, I could be being dumb and maybe I've missed something obvious?...