Study On The Structured Generalization Method Of Contour Based On Terrain Characteristic Lines

With the development of computer technology and the deepening of application and research of geographic information system, map generalization has already become an important issue of cartography. Landscape feature is one of the important elements of the map, and contour is the main form of describing landform, so contour generalization is an important research content of map generalization.Contour generalization is creating contour at small scale from the large scale, which has great significance for the efficient utilization of GIS database and also help to save data storage space, to reduce the operation time and expenses in data acquisition, data updating and so on. In addition, the contour is a kind of complex curve elements and studying contour generalization methods can be referred by the comprehensive of other curve elements. Thus, the contour comprehensive has an important practical value. The contour generalization algorithm can be divided into two categories:node compress methods based on a single curve and group-ped contour generalization, to some extent, these algorithms can complete contour generalization, but these algorithms still have its own limitations. On the topographic map, the contour describe geomorphologic shape by a group of spatial related and similar shaped curves, so studying grouped contour generalization has more practical meaning.Analyzing the current generalization algorithm, this paper mainly studies the structured generalization based on terrain characteristic lines. The content includes the following aspects:generating grid DEM data by contour, extracting the terrain characteristic line based on the surface water physical simulation analysis algorithm, analyzing the method to determine resolution and collect water threshold, and researching the way to process pseudo valleys and flat valley line; Other works are studying a series of problems in structured generalization, such as the evaluation of valley line, and identification of small valley and removing of tiny bending. Establishing hierarchical tree of valley line of the study area is another task, by designing the corresponding algorithm to realize contour generalization; Using Douglas-Peucker algorithm to complete the contour generalization, and evaluating the effectiveness of the structured generalization algorithm is realized by comparing and analyzing the results of both algorithms.The character of the paper is grading handling pseudo valley, which is choosing small bending curve according to the quality and quantity index,and finally analyzing and evaluating results from geometry and terrain attributes of contour. According to the analysis of the experimental results, the structured generalization method not only can effectively remove the small valley and preserve the important topographic characteristics, but also has the higher comprehensive efficiency and precision, and provide the reference for the further study of contour generalization.