A scanning triangulation-based laser range-finder is described, along with a preliminary version of an algorithm for 3-D object recognition. The ranging camera employs a novel design which should ultimately enable a range sample rate of approximately 100 kHz with an accuracy of lcm at ranges <3m. The system employs a spherical coordinate scanning geometry; a laser beam emerges vertically from a hollow shaft and is reflected by a cubic mirror rotating on a horizontal shaft, yielding a vertical (polar angle) scan. A motor rotates the entire system through a slower 360° azimuthal scan. A detection system including a slitted wheel and photo-multiplier, located 1/2 meter above the mirror, repeatedly measures the angle between the vertical and the line of sight to the laser spot. This and the vertical scan angle is used by an LSI-ll computer to compute range. The field of view is a broad "equatorial" band of nearly 3π steradians. An algorithm is presented for recognition of objects known to the system. The surface of each object is approximated by a union of convex polyhedra, represented as a Boolean combination of linear inequalities. A shell is produced Enclosing the surface but not the interior. Then sets of contiguous points from a range-picture are tested for consistency with some rotation and translation of the polyhedral model of each object. The algorithm is tolerant of occlusion and random errors.
Frank Pipitone, Frank Pipitone,
"Three-Dimensional Object Recognition System: Ranging Camera And Algorithm", Proc. SPIE 0205, Image Understanding Systems II, (21 February 1980); doi: 10.1117/12.958164; https://doi.org/10.1117/12.958164