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Curved reconstruction output, due to bad camera optimization?


We flew a mapping flight using the Pix4d iOS app and a DJI Mavic 2 Zoom. We then tried to process the images using Pix4dCloud. The resulting point cloud / mesh is curved in a way that does not reflect reality:

Looking at the quality report, I can see that the camera optimization deviates significantly from the initial assumption:

The computed image positions also show the same deviation from the positions recorded in the EXIF tags:

Since I am running the reconstruction in Pix4dCloud, I have no ability to change any processing settings. Using a trial license, I tried to re-run the reconstruction using Pix4dMapper. I followed the advice provided in Curved Output after initial processing - #2 by Pix4D_Alumni_MV and changed the camera shutter model to “linear rolling shutter”, and the camera optimization to “all prior”.

After re-running the processing, the quality check initially looks promising, with a much lower relative difference in camera parameters:

However, the reconstruction is still curved:

And the optimized camera positions still deviate from the image geo tags:

Here is the report about the rolling shutter optimization. Some of these don’t seem plausible, given the flight path of the drone.

What can we do to get a valid reconstruction out of these images?

What can we do when we do the mapping flights to avoid these issues in the first place? (An obvious suggestion would be GCPs, however, I don’t think that addresses the root cause of the issue, considering that the images’ geo tags are quite accurate but are then “optimized” to something wrong. In other words, trusting the information that is already there would in fact improve the solution).

Thank you for your help!