AN IMPROVED METHOD OF DIGITAL IMAGE CORRELATION

An improved digital image-correlation system has been designed with practicality and efficiency as the major considerations. The imagery is represented within the computer as discrete density values spatially located using a scanning microdensitometer. The system is designed to better use the inherent geometric relationships between the image planes and object space in searching for conjugate imagery on overlapping photographs. Initially, two-dimensional density difference algorithms and enlarged search areas are used to correlate passpoint imagery needed to compute the relative orientation parameters of the photographic system. The epipolar geometric relationships for the stereopair are then calculated and used to better estimate the respective locations of conjugate imagery. Searching for corresponding imagery along epipolar lines, which contain only x-parallax, reduces search time significantly and improves the chances for successful correlation. Elevations are simply interpolated from match-point locations which determine the amount of image point x-parallax along these lines. The horizontal position of final object space coordinates then are determined independent of any residual y-parallax contaminating the system. /Author/