The optical flow of planar surfaces.

The human visual system can recover the 3-D shape of moving objects on the basis of motion information alone. Computational studies of this capacity have considered primarily non-planar rigid objects. With respect to moving planar surfaces, previous studies have shown that the planar velocity field has in general a two-fold ambiguity: there are two different planes engaged in different motions that can induce the same velocity field. The current analysis extends the analysis of the planar velocity field in four directions: (1) the use of flow parameters of the type suggested by Koenderink and van Doorn (Optica Acta, 1975, 22, 773-791), (2) the exclusion of confusable non-planar solutions, (3) a new proof and a new method for computing the 3-D motion and surface orientation (4) a comparison with the information available in orthographic velocity fields, which is important for determining the stability of the 3-D recovery process.