Position determination using generalized multidirectional gradient codes

With the assumptions that P1 is a subpicture of P2 (in particular, P2 covers a much larger area than P1), and P1, P2 are contour maps each characterized by a set of magnitudes at regularly spaced discrete points over a rectangular area, a method of determining the possible location of P1 in P2 is described. The method is based on first deriving generalized multidirectional gradient or conjugate-gradient codes for P1; a contour map for P2 having the magnitude (c*) of the center point of P1 as one of the isopleth values is then generated. For each point on all c*-isopleths, a 2-level classifier is used for determining the possible location of P1 in P2.