DNESYS--An Expert System for Automatic Extraction of Drainage Networks from Digital Elevation

The determination of drainage networks and drainage basins is one of the more tedious yet important uses of topographic maps, and geographic information systems are now used extensively as a manual aid to facilitate that task. However, the wide availability of digital elevation maps has stimulated attempts to automate the process even further. In this paper, the problems that arose in earlier programs to map drainage systems are analyzed in detail. An expert system called the Drainage Network Extraction System (DNESYS) is described which uses both local operators and global reasoning to extract drainage networks and ridge lines. A stream representation called a parameterized directed graph (PDG) is constructed to model a drainage system. The construction of a model begins with an initial pixel labeling procedure. Then a network tracing and property measurement procedure converts the 2-D low-level labeling information into a symbolic database for high -level processing. By applying Dempster- Shafer evidence theory, evidence collection and uncertain reasoning are performed against the DNESYS knowledge-base that contains the drainage system model and the organized expert knowledge. By discarding erroneous information and supplying missing information, DNESYS produces a complete PDG which can be converted into the final drainage system.