Rotation-invariant optical recognition of three-dimensional objects

An automatic method for rotation-invariant three-dimensional (3-D) object r ecognition is proposed. The method is based on the use of 3-D information c ontained in the deformed fringe pattern obtained when a grating is projecte d onto an object's surface. The proposed method was optically implemented b y means of a two-cycle joint transform correlator. The rotation invariance is achieved by means of encoding with the fringe pattern a single component of the circular-harmonic expansion derived fi om the target. Thus the meth od is invariant for rotations around the line of sight. The whole experimen tal setup can be constructed with simple equipment. Experimental results sh ow the utility of the proposed method. (C) 2000 Optical Society of America OCIS codes: 100.4550, 100.6890, 100.5760.