Passive Determination Of Three-Dimensional Form From Dynamic Imagery

A critical problem for the cruise missile is the development of image processing techniques applicable to target acquisition for an autonomous terminal homing system which depends upon an on-board comparison of a sensed scene with a stored replica of a predesignated target area. Extensive efforts are currently in progress to develop algorithms based upon area correlation and feature matching techniques for accurate registration of sensed and reference imagery. Image intensity matching depends upon several unpredictable factors such as time of day or year, weather, changes in scale, viewpoint, and perspective, spectral and sensor characteristics, etc. In contrast, one of the most invariant properties of a scene is its geometric form. A sensed height distribution of a target scene can be determined passively from dynamic imagery by exploitation of the concept of motion stereo: over a sequence of frames, the scene is continuously viewed from changing observation points as the vehicle moves. The accuracy to which elevations can be determined is based upon sensor and vehicle parameters, geometry, image characteristics, and the nature of the processing algorithms. In principle, all that is required for depth determination is a single pair of frames. In practice, however, real imagery is corrupted by noise, sensor jitter, imperfect knowledge of vehicle trajectory, etc., and it is necessary to infer elevation from a successively refined statistical best estimate obtained from averaging results over several pairs of frames. Preliminary results of motion stereo process-ing to obtain object depth from image coordinate trajectories (obtained by correlation tracking) will be described, and efforts to extend the techniques to computationally efficient methods of area processing will be discussed.