Application of shape-preserving spline interpolation to interactive editing of photogrammetric data

Abstract

The Integrated Photogrammetric Instrument Network (IPIN) is being designed and developed by the Defense Mapping Agency Aerospace Center in St. Louis, Mo. to meet database demands for terrain elevation information. IPIN is a network of computers and instrumentation dedicated to digitizing and editing photo-source terrain data [1]. Editing procedures are required because of digitizing errors inherent in the data-collection process. Some of these errors are random; others are systematic and predictable. The techniques of one of the editing procedures being developed may find application elsewhere. The procedure of interest here involves smoothing raw data that have been collected by the operator of an analytical stereoplotter. When digitizing geomorphic features from aerial stereophotographs, the double-line drain (DLD) presents special problems. The digitizing of a DLD (a relatively broad river or stream) requires specifying trlples (x,y,z) (latitude, longitude, elevation) at points spaced along the length of each shoreline. The drain boundaries thus collected usually have acceptable latitude and longitude values. The elevation values, however, require smoothing.