Support Website Contact Support Blog

Images calibrated when processing single strip but not for the whole block

Hello everybody,

 

I have a problem when I trying to process the whole block of aerial images.

Most of the 238 images calibrate, actually there are only 10 not calibrated. Unfortunately 6 of these cover an area which I absolutely need in my DSM. 

The strange thing is when I do process the strip containing the uncalibrated images it matches them without any problems showing proper results.

 

I would be really greatful if you could help me with that issue as repeating the flight is not possible.

 

best regards and thanks in advance!

 

Max

Hello Max,

Does the project have image geolocation? Is there enough overlap between these 10 images and the rest of the images that are calibrated? 

If the project does not have image geolocation and there is a break in the overlap between the images (overlap not sufficient or not consistent), this can lead to uncalibrated images. On top of that, if the terrain is homogeneous, even with image geolocation a discontinuity in the overlap can cause issues.

What you can try to do is:

  1. Process step 1 for the 228 images together and the 10 images separately.
  2. Mark at least 3 common manual tie points on each sub project and reoptimize. Make sure that these manual tie points share the same name in both sub projects and that they are in the common area. It is recommended to mark at least 5 MTPs well distributed in the common area.
    For more information, please check:  https://support.pix4d.com/hc/en-us/articles/entries/57731727.
  3. Merge the sub projects. For more information, please check: https://support.pix4d.com/hc/en-us/articles/entries/27053947

Best regards,

Thank you very much for the advice!

I solved the problem, partly by doing what you described in your post. Here a description as it might possibly help someone else:

 

The problem lies in the nature of the surface depicted in the images. As it is a glacial area there are many areas that are snow covered. So as there basically is no distinctive structure in large areas it seems hard for the matching algorithm to automatically find a sufficient number of tie points.

A further problem I identified was that the structure that IS visible (like glacial mills and single rocks) are of such generalized structure that they match in other images that do not cover the particular geolocation of the uncalibrated images. So for most of the images the problem was that a higher number of false matches were found than actual true matches.

What I now did was I processed the single strips that contained the uncalibrated images (as those were spread all over the whole area of interest) and thus decreasing the number of possible false matched patterns. In a single case I had to use manual tie points. By iteratively adapting the camera parameters I was finally able to calibrate the failed images in the single strips. I then merged the strips one after another with the whole block.

This lead to only 3 images left that I am not able to calibrate. This is (from my guess) because they consist of mostly snow covered areas. As they are in the border region of the block and do not contain information I need (as they are not part of the overall area of interest) I can live with them not being calibrated.

Thank you again for your help!

Max