Recognition of planar shapes by a semi-differential invariant for moving triangles (Q1872976)

For recognition of moving triangles, a method using the semi-differential invariant for pseudo-perspective projection is constructed requiring to catch two of original angles at vertices by simple and fast computation from photo information. The method works also for smooth contours and lines and recognizes local figure by very simple computations. The main idea is to consider image trajectories of circles placed properly. The method is applied to the recognition of three-dimensional tetrahedrons.