Disturbing Moiré effects in photogrammetric setups using passive structured light

With structured light methods every object point is illuminated with a temporally changing radiance and the scattered light is synchronously captured by several detectors. In order to reconstruct an object point it is necessary to determine homologous points. If homologous points are searched by analysing pairs of single-pixel features the discrete nature of CCD arrays causes a spatially modulated disturbance of the point mapping: The thought overlap of two CCD arrays on the object corresponds to a superposition of two similar periodical grids. Thus there is a spatially varying degree of overlap of homologous pixel-pairs. Depending on the used method this Moiré effect may reduce reconstruction quality. We demonstrate this effect with a time-correlation algorithm on data generated by a passive structured light method using statistical patterns. Methods to decrease the effect are discussed. Furthermore a classification of pixel-pairs is proposed.