Dear pix4d team,
Some time ago we processed an aerial data set in the Netherlands with pix4d 2.0.89.
Recently, we acquired a couple of GCPs in the area to verify the data sets accuracy properly.
Subsequently, we processed the data set again (in 3.1.22), and it turned out that there was a rather large offset between the GCPs and the aerial data before adjustment.
The GCPs, however, perfectly fit to the data set processed earlier with the older version (2.0.89),
We were wondering if there were some changes regarding the height reference, as we think this might be the reason for this issue.
In 2.0.89, the data has been processed using the Bessel ellipsoid in the RD New system. Of course, we used the same reference again with the newer version.
Thank you for your help! Please let me know if you need further information.
Hi Phillipp,
If we correctly understood, the same images were used with version 2.0.89 and 3.1.22. The Ground Control Points (GCPs) were collected after the images were acquired, so we assume they were measured on features of the area that are visible in the images.
If the GCPs seem to exactly match (without a shift) in the project created in 2.0.89 but that there is a shift in the project created with 3.1.22, it could be that there is a difference in how the coordinate systems were defined in the project. There are three coordinates systems to check:
- image coordinate system
- GCP coordinate system
- output coordinate system
For each of these, we would double check if the horizontal and vertical coordinate systems are the same in both projects. The vertical coordinate system can be modified by ticking the “Advanced Coordinate Options” checkbox. More about how to modify the coordinate systems in this article: https://support.pix4d.com/hc/en-us/articles/202560029
A trick to double check if the coordinate systems match would be to double check the summary of the coordinate systems in the Quality Report.
If the issue is not related to the definition of the coordinate systems, we would need to further investigate both projects. In this case, please submit a request and add the Quality Report and Log files of both projects: https://support.pix4d.com/hc/en-us/articles/hc/en-us/requests/new?
Regards