Add method to align multiple DEMs/PC together

[adehecq]

Some algorithms exist to align multiple DEMs/PCs together (e.g. from a single or multiple overlapping flight lines). See e.g. this paper and this script.

At least, the basic would be to:

1. Create a centroid of all PCs
2. Coregister each individual PC to the centroid
3. Iterate 1 and 2 until the mean distance to the centroid reaches a minimum

This is worth testing!

[rhugonnet]

Great, more work :wink: ! Can't wait to have all of those implemented :)