Grid Method, Moiré and Deflectometry
Abstract
The grid method has a very simple basic principle [HUN 98, PAR 90, DAL 91, SEV 93]. Even if it is independent of image formation and acquisition, the grid method is usually classified among optical techniques. The measurement is based on a purely geometrical phenomenon: a geometrical grid is affixed to a substrate. If the substrate deforms, the grid follows any local movement. The distorted grid will carry the displacement information, and its image can be analyzed using a classic modulation/demodulation approach.
In recent times, acquisition and image-processing capabilities, as well as advances in image sensor quality, have led to renewed interest for this particular technique because it is relatively easy to implement. The quality of phase detection algorithms provides excellent measurement resolution. From a metrological point of view [ZHA 01, SUR 05], this technique is easier to characterize than the digital image correlation.