Presentation of two optical correlation-based measurement techniques for surface deformation: PROPAC and REPAC

Abstract

The objective of this study is to describe two measurement techniques: the Projected Pattern Correlation (PROPAC) and the Reflected Pattern Correlation (REPAC). As in the fringe projection technique the surface of a large area is determined simultaneously, but instead of using several images of different fringes for the solution of the correspondence problem we use only one measurement image with random dot patterns and cross-correlation algorithms. This new concept has the advantage that we can use the software and algorithms of the well-developed Particle Image Velocimetry (PIV) technique for flow measurements. The PIV algorithms have proved to be very fast (10 ms image acquisition, real-time measurements are possible) more robust and highly accurate. Due to the random character of the dot pattern the measured displacement vector between a reference surface and the deformed surface by means of cross-correlation is always unique.