How to Align and Subtract Pre- and Post Surface with an Offset?

Hi,

I am currently facing a small problem and hope that someone here can help me.

I have placed 4 indents in a surface in the shape of an rectangle and scanned the surface afterwards (Prescan). Than I have worn out the surface between the 4 indents and scanned it again afterwards (Postscan).

Now I would like to substract the prescan from the postscan and therefore put the 4 indents from post and prescan exactly on the same position on top of each other. So maybe one of you can tell me how I can tell Matlab to align the four indents of both scans exactly, so that I can then subtract both scans from each other and get a "wear volume".The problem is, there is an offset bewetten both scans.

Which might help: The four indentations are the lowest points of the surface, so you could probably tell Matlab to align the lowest point of the pre-surface with the lowest point of the post-surface, and the same for the other indentations and then move all points. However, I do not know how to tell this Matlab. Might be in in the form of: Find lowest point Pre and align it to lowest point Post, then find second lowest point Pre and so on.

I already know how to display the surfaces with surf and also how to put both on top of each other with "hold". I tried Image registration and I tried load the data via Load File, which looks very good at first. However, it does not seem to find any matches there (Dected 0 and 0, Matched 0) and so I can not use Register Images.

Thanks a lot for your help!

Best regards

Lukas