Topographic comparator

• US 4,294,544 A
• Filed: 08/03/1979
• Issued: 10/13/1981
• Est. Priority Date: 08/03/1979
• Status: Expired due to Term

• Current Assignee: Bruce R. Altschuler, John Taboada, Martin D. Altschuler
• Original Assignee: Bruce R. Altschuler, John Taboada, Martin D. Altschuler
• Inventors: Taboada, John, Altschuler, Bruce R., Altschuler, Martin D.
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US06/063,500
• Time in Patent Office: 802 Days
• Field of Search: 356/1, 356/2, 356/345, 356/352, 356/354, 356/355, 356/356, 356/357, 356/358, 356/363, 356/376
• US Class Current: 356/610
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 11/022 by means of tv-camera scanning
• CPC Class Codes: G01B 11/2513 with several lines being projected in more than one direction, e.g. grids, patterns

Abstract

Three-dimensional (3-D) topographic data defining a remote surface in terms of the 3-D positions of M×N sample points on that surface may be obtained by (1) illuminating the scene with an array of M×N (simultaneous) laser beams, (2) sequencing the array of laser beams through a series of mathematical patterns (space coding) by means of a programmable electro-optic shutter, (3) recording by an imaging device the illumination reflected from the surface during the projection of each mathematical pattern, (4) analyzing the images to obtain the three-dimensional locations of each of the M×N illuminated points on the surface which are visible to the camera or imaging device, and (5) determining which of the laser beams in the array are not visible to the imaging device. (N and M are any positive integers consistent with the device proposed; typically M=N=128, so that M×N=16384 points.) Mechanization for rapid three-dimensional mapping of the surface involves an array of laser beams illuminating the surface, a programmable electro-optic shutter to switch on and off subsets of laser beams in the array and thereby to input the space code projected on the surface, a (usually narrow bandpass) video camera to capture the reflected images of the space coded surface from a given perspective (and if necessary from various other aspect angles), and a device to synchronize the electro-optic shutter with the video camera. Space coding of the light beams is used to correlate each spot seen on the surface with the corresponding beam in the laser beam array. A space code for an array of beams arranged in M rows and N columns reduces the number of images, I, necessary for correlating all light spots seen on the surface to I=l+log₂ N where N is also the number of columns of the electro-optic shutter whch can be individually switched. The device achieves 3-dimensional topographic mapping much faster than laser rangefinder and optical devices because it can locate M×N surface points with only l+log₂ n images (or patterns); it has much greater signal to noise capability than conventional light devices (it can work in daylight for a great variety of surface textures and uses non-moving, vibration-free components during data collection), and it is unambiguous in its mathematical results for all illuminated and visible surface points within its operating range.

The invention differs from stereophotogrammetry by using one "active" device (the laser beam array) and one passive camera rather than two passive cameras as in conventional stereophotogrammetry. A system of several "active" devices (laser beam arrays) and several passive cameras is also comprehended if the object to be interrogated is very rough, convoluted, or has many sides.

Claims