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Adaptive optical three-dimensional measurement with structured light
The described 3-D measurement system with fringe projection applies the principle of uniform scale representation by the exclusive use of phase measurement values for the coordinates of each point. The test object is successively illuminated with a grating structure from at least three different directions with a telecentric system, where gray code is combined with five 90-deg phase shifts. A CCD camera records the intensity distribution of the fringes that appear as intersection lines on the surface of the object. This provides the linearly independent absolute phase values that are necessary for the calculation of the coordinates. Note that all coordinates (x y z) are determined with the same accuracy. To compensate the influence of specular reflections or shadowed areas up to 15 light projection directions can be used. Moreover, the object can be rotated around a second axis, yielding other views of the object. Thus we acquire different patches of the object that aretransformed into a global coordinate system without any interactive user help. During this procedure, correlation methods or special points are not necessary. The calibration of the 3-D orientation of the second axis is realized with a special calibration body.