Abstract: A system for determining the position of an object in which a moving periodic pattern is projected onto the object. A sensor on the object generates a sensor signal related to the periodic pattern. A reference signal is generated relating to the position of the moving periodic pattern. The sensor signal and the reference signal are compared to determine the position of the object. The pattern may be generated by projecting light through two gratings which are separated and have the same pattern. Errors created by instability or nonisotropy can be corrected employing a third grating having a different pattern and generating a correction value related to the difference between the position of the object determined employing the pattern generated by the two gratings and the pattern generated by the third grating. The moving nature of the pattern may be created by employing a fixed projector and a moving mirror.

Abstract: A range imaging system in which a periodic pattern is projected onto the scene to be imaged. Three frames of intensity values are collected as the pattern shifts 120.degree.. The phase by which variations in range cause portions of the pattern to shift are determined from the three frames of data as being proportional to range. To generate the phase information, the intensity value for each pixel in the third frame is subtracted from intensity values of the same pixel of the first and second frames. The arc tangent of a function of these difference values represents the phase shift, and thus range.

Abstract: A range imaging system in which a moving periodic pattern is projected onto the scene to be imaged. The phase by which variations in range cause portions of the pattern to shift are monitored to develop range data. A television camera offset from the axis of illumination generates four frames of intensity values. The moving pattern shifts one-quarter cycle with respect to the pattern between each of the frames. The data from the third frame is subtracted from the first frame and the data from the fourth frame is subtracted from the data of the second frame to cancel the effects of background illumination. The first difference represents a sine signal and the second difference represents a cosine signal. The arc tangent of the quotient of these values represents the phase, and thus the relative range of various points in the image. The moving pattern can be generated by either a translating plate or rotating disk which has a periodic variation in transmissiveness.