I posted this in the Pix4d Desktop thread. re-posting here because I have received any responses and this topic fits better.
I have 23 GCPs in a project with 542 images, covering 90 acres with an average GSD of 3.67cm/1.44 in. The GCPs were surveyed with terrestrial RTK GPS instruments. I’m getting very poor correlation between the surveyed GCP coordinates and the computed coordinates. The Theoretical error is low but the error to GCP initial position is high in the X and Y around 2-3x the GSD at almost all GCPs in either the X or Y directions. The theoretical and error to initial Z position are actually great - equal to or less than the GSD.
That’s with using all GCPS as 3d GCPs. If I mark any of them as check points the X, Y error relative to the initial position is more like 5x the GSD.
What am I doing wrong? I’ve checked all of the GCP coordinates and they match what the surveyor delivered from his data collector. What else could be the problem?