CloudCompare forum

Hi,
I'm trying to align two point clouds, a laser point cloud and a photogrammetric one.
First I aligned the two clouds with the Align(point pairs picking) tool. I had a fineal RMS of 0.04 m. But when I tried to improve the registration with the Fine Registration (ICP) tool, the final RMS always increases (from 0.04 to 0.20). What could be the problem?

Actually, the first RMS is computed with only a few points (the one you selected with the Align tool, i.e. 4, 5 or even 12 in the best case).

On the other hand, the RMS computed by the ICP tool is computed on up to 50 000 points (or more if you have increased the 'random sampling' parameter). Therefore it's not that surprising that the RMS is higher.

However, with the ICP tool, make sure the 'overlap' parameter is realistic, otherwise non-overlapping areas might shift the final registration a little bit.