too large marker coordinate errors

[jan]

Hi,

I'm working on a large project (5000 photos). I want to make 5 chunks of 1000 photos each, and merge these chunks later on. There are no camera coordinates, but I have 9 GCPs.

Thus far I aligned, made a mesh and optimized a first chunk. 4 GCPs are visible on this chunk, and the GCP error coordinates are very good (errors are less than 0.005 m, while the chunk itself is bigger than 100 m in both dimesions).

Now, for the second chunk, only 2 GCPs are visible, but these 2 GCPs are both also visible on the first chunk. The strange thing is that for the second chunk, after giving in the marker coordinates in the ground control pane, the GCP erros are huge (> 100 m for 1 of the 2 markers). How come this is possible as the marker errors are tiny in the first chunk (for the same two markers)?

regards,
Jan   

[Alexey Pasumansky]

Hello Jan,

You need at least three reference points to set up a coordinate system.

Please also note that the errors in the first case are low due to only three points are used.