Moire topography has long been known as a useful optical means for three-dimensional metrology. In recent years its practical application is growing as computer-integrated image processing is extensively available. Fringe analysis for moire topography started with lateral image processing, in which local intensity maxima and minima are traced identify absolute fringe orders and then relative fringe phase are subsequently decided using appropriate interpolation. However, this fringe-following processing yields many difficulties in handling complicate interferograms with dense appearance of fine fringe and even it is not eligible for target surfaces of varying reflectance. To cope with the problems, there has been an attempt to adopt phase-shifting technique in moire fringe analysis, as successfully done in electromagnetic waves interferometry. In the adoption of phase shifting technique to moire fringe analysis, the equivalent wavelength of the moire system is the measurement basis. So to achieve precise measurement its value must be determined very accurately. Newly proposed calibration method using a special phase measuring algorithm, named A-bucket algorithm, and laser interferometer is a very useful means in determination of that value. Several experimental cases are discussed to demonstrate that a measuring accuracy in order of 0.001mm can practically be achieved. Next a phase-shifting projection moire method particularly intended for high speed three-dimensional measurement of free-formed objects is presented. Emphasis is on realization of phase-shifting fringe analysis in projection moire topography using a set of line grating pairs designed to provide different phase shifts in sequence. Further a time-integral fringe capturing scheme is devised to remove undersirable high frequency original grating patterns in real-time without time-consuming software image processing. In using phase-shifting technique, there exists an inherent problem, 2-π ambiguity problem which limits maximum measurable step height. Newly proposed multiple phase-shifting grating projection moire topography is capable of overcome this problem successfully, in addition, has advantage of absolute 3-dimensional contouring.
