Semi-local invariants

Geometr ic invariants are shape desrriptors that remain unchanged under geometric transformations such as projection, or change of the viewpoint. In [,?I we devc’loped a new method of obtaining local projert ive antl affine invariants for a general curve without any correspondences. Being local, the invariants are much Ii ss sensitive to occlusion than global invariants . The iniiariants computation is based on a cunonicul method This consists of defining a canonical coo7.dinate sys tem using intrinsic propert ies of the shapc, independently of the given coordinate sys tem. Since this canonical sys tem is indept-ndent of the oriyinul one, i t is invariant and all quantities defined in it arc invariant . Here we present a furth.er developnient of the method t o obtain local semiinvariants , thud is loi d rnvtrriunts for curves with known correspondencrs. Several conjigurations are treated: curves with knoion correspondences of one or two feature points or lines.