4-MAP ABSOLUTE DISTANCE CONTOURING

A new method called four-map absolute distance contouring, based on th e shadow moire technique, is described, In this system, the period of a sinusoidal grating is varied through its rotation, with the effect t hat the phase of the moire pattern is also changed. By selecting suita ble rotation angles, four images at different grating positions are ac quired, from which the absolute distance from the object to the gratin g can be determined. The theoretical analysis is presented for the met hod, which has been verified by suitable laboratory experimentation. T he measurable range is directly proportional to the period of the grat ing and inversely proportional to the angles through which the grating is rotated. The results show that the method is fast and accurate. (C ) 1997 Society of Photo-Optical Instrumentation Engineers.