In the systems and methods of this invention, after two images are obtained, these images correlated only at offset positions corresponding to a sparse set of image correlation function value points. One or more correlation function value points of the sparse set will have correlation values that indicates that those points lie within a peak portion of the correlation function. Once one or more such correlation function value points are identified, these images are correlated at offset positions corresponding to a second, dense, set of points of correlation function value points. The correlation function values of these correlation function value points are then analyzed to determine the offset position of the correlation function peak.