Laser Electro-Optic System For Rapid Three-Dimensional (3-D) Topographic Mapping Of Surfaces

Abstract

A method is described for high-resolution remote three-dimensional mapping of an unknown and arbitrarily complex surface by rapidly determining the three-dimensional locations of M x N sample points on that surface. Digital three-dimensional (3-D) locations defining a surface are acquired by (1) optically transforming a single laser beam into an (expanded) array of M x N individual laser beams, (2) illuminating the surface of interest with this array of M x N (simultaneous) laser beams, (3) using a programmable electro-optic modulator to very rapidly switch on and off specified subsets of laser beams, thereby illuminating the surface of interest with a rapid sequence of mathematical patterns (space code), (4) image recording each of the mathematical patterns as they reflect off the surface using (a) a wavelength-specific optically filtered video camera positioned at a suitable perspective angulation and (b) appropriate image memory devices, (5) analyzing the stored im-ages to obtain the 3-D locations of each of the M x N illuminated points on the surface which are visible to the camera or imaging device, and (6) determining which of the laser beams in the array do not provide reflec-tions visible to the imaging device. Space coding of the light beams allows automatic correlation of the camera image (of the reflected spot pattern from the surface) with the projected laser beam array, thus enabling triangulation of each illuminated surface point. Whereas ordinary laser rangefinders aim and project one laser beam at a time and expect to receive one laser beam reflection (bright dot image) at a time, the pres-ent system is optical (nonmechanical and vibration-free) and can collect all the data needed for high-resolution 3-D topographic mapping (of an M x N sample of surface points) with the projection of as few as 1 + log2N light patterns. In some applications involving a rapidly changing time-dependent environment, these 1 + log2N patterns can be projected simultaneously in different wavelengths to allow virtually