Evaluation of the Coastal Features Mapping System for Shoreline Mapping

摘要

Since many coastal areas are subject to frequent change due to environmentalconditions or commercial development, it is often difficult to fulfill the optimum requirements for ground control when mapping from aerial photographs. For this reason, a series of tests were devised to evaluate the accuracy of the Coastal Features Mapping System (CFMS) for typical shoreline mapping applications encountered by the US Army Corps of Engineers. Major variables tested included the number of ground control points (GCP's) employed in the solution and their distribution. Ground control points digitized from 1:24,000 scale US Geological Survey topographic maps were used in various combinations to orient 1:9,600 scale aerial photographs for coordinate retrieval. It was found that the accuracy of X-, Y-coordinates determined from the photographs is governed by the distribution and accuracy of GCP's. Maximum accuracy is obtained when all measured points are within the area bounded by the GCP's. Although at least four GCP's are required for the solution, additional points allow possible mistakes to be identified and corrected interactively. In all tests, the errors were consistent with those associated with 1:24,000 scale base map as defined by National Map Accuracy Standards. The user's guide contained adequate information about overall program operation, but lacked sufficient guidance for first time users.