Match filter based on the correlation surface. Starting from an approximate alignment (e.g. affine), for each vertex of the spring mesh, an offset is searched calculating the PMCC coefficient r of a block at all possible x,y translations in a given local vicinity over the overlapping image. The above windows display six examples of such correlation surfaces for translations in a square region with the origin in the middle. The PMCC coefficnet r is grey-coded in the range from -0.7 to 0.7. The candidate for the translational offset is the translation with maximal r. Candidates are rejected if either r was too low (not similar), there was more than one maximum with very similar r (ambiguous), the maximum is not well localized in both dimensions (an edge pattern that fits everywhere alongside the edge).