Implement CrossCorrelation metric

[riaanvddool]

Based on this paper:

www.isprs.org/proceedings/XXXVII/congress/7_pdf/6_WG-VII-6/03.pdf

[riaanvddool]

Mm, not sure that the method described in the paper returns an error metric for all image pixels...

[nfaggian]

Window function on each pixel, often achieved by performing an fft.

[stefanv]

Just to make sure I understood the paper correctly: this is an iterative method?

They do not describe what happens for out-of-boundary pixels... could be quite important (it certainly is when minimising the sum of difference squared).

[nfaggian]

parameter search wrt to cc metric, not clear what to do with the correlation window on boundaries - I suspect we just mask out missing data or smooth out boundaries to fill in the gaps.