Fit Point Clouds Pulls Point clouds apart

dsmithdsmapping09

How do you use the ICP method to merge two point clouds together? There are some slight differences between two different point clouds Im working with but for some reason when I run the ICP method it takes the point cloud I am trying to move and shifts it further away. Why would it be doing this? There is plenty of overlap, like I said theyre within about a foot of each other.