A new method called four-map absolute distance contouring, based on the shadow moire´ technique, is described. In this system, the period of a sinusoidal grating is varied through its rotation, with the effect that the phase of the moire´ pattern is also changed. By selecting suitable rotation angles, four images at different grating positions are acquired, from which the absolute distance from the object to the grating can be determined. The theoretical analysis is presented for the method, which has been verified by suitable laboratory experimentation. The measurable range is directly proportional to the period of the grating and inversely proportional to the angles through which the grating is rotated. The results show that the method is fast and accurate.
Michael J. Lalor,
David R. Burton,
Michael Mason Shaw,
"Four-map absolute distance contouring," Optical Engineering 36(9), (1 September 1997). https://doi.org/10.1117/1.601480