A proposed optoelectronic system, to be mounted aboard an exploratory robotic vehicle, would be used to generate a three-dimensional (3D) map of nearby terrain and obstacles for purposes of navigating the vehicle across the terrain and avoiding the obstacles. Like some other systems that have been, variously, developed and proposed to perform similar functions, this system would include (1) a light source that would project a known pattern of bright spots onto the terrain, (2) an electronic camera that would be laterally offset from the light source by a known baseline distance, (3) circuitry to digitize the output of the camera during imaging of the light spots, and (4) a computer that would calculate the 3D coordinates of the illuminated spots from their positions in the images by triangulation.
The difference between this system and the other systems would lie in the details of implementation. In this system, the illumination would be provided by a laser. The beam from the laser would pass through a two-dimensional diffraction grating, which would divide the beam into multiple beams propagating in different, fixed, known directions (see figure). These beams would form a grid of bright spots on the nearby terrain and obstacles. The centroid of each bright spot in the image would be computed. For each such spot, the combination of (1) the centroid, (2) the known direction of the light beam that produced the spot, and (3) the known baseline would constitute sufficient information for calculating the 3D position of the spot.
Concentrating the illumination into spots, instead of into lines as in some other systems, would afford signal-tonoise ratios greater than those of such other systems and would thereby also enable this system to image terrain and obstacles out to greater distances. The laser could be pulsed to obtain momentary illumination much brighter than ambient illumination, and the camera could be synchronized with the laser to discriminate against ambient light between laser pulses.
This work was done by Curtis Padgett, Carl Liebe, Johnny Chang, and Kenneth Brown of Caltech for NASA's Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-40611
This Brief includes a Technical Support Package (TSP).
Mapping Nearby Terrain in 3D By Use of a Grid of Laser Spots
(reference NPO-40611) is currently available for download from the TSP library.
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