Semiautomatic Pass Point Determination Using Digital Techniques.

摘要

This research note describes a study performed at CSL (Computer Sciences Laboratory) to evaluate the feasibility of measuring pass points on overlapping imagery using digital correlation methods instead of utilizing conventional stereo viewing procedures. Rather than investigate the entire problem of automatic pass point mensuration including the logistics and electronic aspects,this study was limited to the photogrammetric problem. The photogrammetric problem is simply the numerical problem associated with the determination of corresponding points. The logistics aspect of the problem pertains to the organization of pass point data and density data with regard to computer storage and retrieval. The electronics aspect of the problem pertains to the scanner,to the image display system,and to the electronic marking device. The basic idea behind the proposed method is that pass points can be measured more quickly,and hopefully more accurately by digital methods than by conventional methods. It should be possible to evaluate each match numerically in the computer,thus rejecting poor determinations and reducing to zero the probability of having to remeasure the model in a triangulation exercise. Generally,an operator will display corresponding image subsets of a particular model on a display device and will visually select pass points by marking them with a cursor. Density data around a selected point will be read into computer memory,and the match (estimated with the cursor) will be refined by using correlation techniques.