Shape measurement with one fringe pattern recording including a digital master

We present a method in which the 3D shape of an object can be measured and compared to the shape of the digital master of the object, e.g., the computer-aided design model. The measurement is done using a stereo camera system and a single projected fringe pattern. Because the digital master is available, i.e., the expected shape is known, only one projection and image recording is necessary; thus, the method becomes fast. The idea in this work is to find homologous points in the cameras, i.e., points corresponding to the same object point, using the object information. An algorithm to find the homologous points is presented and a method to calculate shape is described. Given the ambiguity due to the fact that the phase in the images is wrapped, there is a maximum deviation from the master that can be correctly detected. An analytical expression for this deviation is derived. Results from the shape measurement of an object both with and without deviations from the digital master are also presented. In these measurements, where the measurement volume is approximately 1 dm3 and the fringe period on the object plane is about 1 mm, the accuracy is ≈±40 μm, and a deviation of max ≈±1.6 mm can be correctly detected.