A hypsocline or interference pattern having a shape and position representing the shape and position of an isoelevation area in a scene is produced from two phototransparent stereo images by directing mutually coherent collimated laser beams to strike the two stereo images. The images diffract the beams and thus transmit image information to the laser beams. The diffracted beams are directed to intersect, and any portions of the two intersecting beams representing the same area in the scene that are in registration with each other provide an interference pattern comprising alternate light and dark lines. The interference pattern has the shape and position of the represented area in the scene. The images are oriented with respect to each other so that the patterns produced represent isoelevation areas in the scene. A relative movement is provided between one stereo image and the beam striking that image to alter the portions in registration and thus provide different interference patterns representing areas at different elevations. The D.C. spatial frequency components are removed from the diffracted beams in order to maximize the difference between the interference patterns representing isoelevation areas and background signals surrounding those interference patterns.
A heterodyne optical correlator allows a correlation function to be computed for plural portions of a stereo pair of transparencies which is normalized to thus reduce the possibility of false correlation peaks. To obtain the correlation function, a pair of stereo transparencies are illuminated by an intense monochromatic light source producing an image at a common image plane in which a detector array is located. The relative path length, between source and transparencies, is periodically modulated producing at plural locations of the detector array plural alternating current signals representing the correlation between the amplitude transmittances at various corresponding locations on the transparencies for a given relative displacement between the transparencies. To normalize this correlation coefficient a second signal is produced by illuminating only one transparency and a corresponding third signal is produced by illuminating only the other transparency. The ratio between the correlation coefficient and twice the square root of the product of the second and third signals is a normalized correlation coefficient. Plotting the normalized correlation coefficient at each of the plurality of points in the transparencies as the relative positioning of the transparencies is shifted allows the correlation function and its peak to be determined. The relative positioning between the transparencies at the correlation peak is a measure of parallax.
A gauge for measuring flatness by utilizing the interference of light is composed of a block having a reference or standard surface of a high flatness and surfaces intersecting the reference surface. Three supporting members are fixedly secured to said surfaces in an appropriate arrangement. Each of three pins which is anchored to respective supporting member has a pointed top portion jut beyond the reference surface. The object or specimen to be tested is rested on said top portions of the three pins to support the specimen with the tested surface extending substantially in parallel with said reference surfaces in opposing position.
