Invariant signatures for planar shape recognition under partial occlusion

A planar shape distorted by a projective viewing transformation can be recognized under partial occlusion if an invariant description of its boundary is available. Research in this area has provided a theory for invariant boundary descriptions based on an interplay of differential, local, and global invariants. Differential invariants require high-order derivatives. The use of global invariants and point matches on the distorting transformations enables one to reduce the order. Trade-offs between the highest order derivatives required and the quantity of additional information constraining the distorting viewing transformations are made explicit