Fourier transform profilometry for the automatic measurement of 3-D object shapes

TLDR

A computer‑based technique for automatic 3‑D shape measurement is proposed and experimentally verified. The method projects a grating pattern onto the object, then Fourier‑transforms and processes it in both spatial‑frequency and space‑signal domains, differing from conventional moiré contouring. The technique achieves higher sensitivity than conventional moiré, automatically distinguishes depressions from elevations, eliminates the need for fringe‑order assignment or interpolation, and is immune to errors from spurious moiré fringes caused by higher harmonics.

Abstract

A new computer-based technique for automatic 3-D shape measurement is proposed and verified by experiments. In contrast to the moire contouring technique, a grating pattern projected onto the object surface is Fourier-transformed and processed in its spatial frequency domain as well as in its space-signal domain. This technique has a much higher sensitivity than the conventional moire technique and is capable of fully automatic distinction between a depression and an elevation on the object surface. There is no requirement for assigning fringe orders and interpolating data in the regions between contour fringes. The technique is free from errors caused by spurious moire fringes generated by the higher harmonic components of the grating pattern.