Research On Evaluating Indexes System Of Contour Simpli-fication Algorithms

Contour generalization is a hot issue in the research areas of cartographic generalization. Contour generalization methods are diverse, and polyline simplification algorithms by computer technology are a kind of effective method for space data compression. At present, there are many polyline simplification algorithms, most of which attain the purpose of reducing date amount by rejecting points that form the polyline. According to the principle of choosing space data and setting the search areas, those methods can be categorized into five kinds:Independent Point Routines, Local Processing Routines, Unconstrained Extended Local Processing Routines, Constrained Extended Local Processing Routines, and Global Routines. Those algorithms will affect the quality of space data in the simplification process, including position accuracy, shape and size accuracy, attribute accuracy etc. Errors which generated from simplification process will vary depending on different algorithms or different compressing ratio. With deepening research in contour simplification algorithm, it is increasingly important to research the evaluation methods of the simplified results.The mainstreaming evaluating methods of data quality is to analyze the changes in geometry and topology, which just regard contours as abstract lines and ignore its geographic features as a carrier of landform information, though such evaluating methods are available for simple comparative and qualitative analysis.This thesis tries to build a universal error evaluating indexes system of Contour Simplification Algorithm, which is based on both the geometrical error and the attribute data error. Geometrical error can be evaluated by length error, displacement error, buffer tolerance and topology error, while the error of geographical attribute data can be calculated and extracted by constructing DEM, then statistical analysis can be processed.This study took the hypsographic map of Biyun'an in the region of Lushan as experimental data, and simplified the contours by 11 common simplification algorithms, then evaluated these algorithms according to the above 11 algorithms.This study demonstrates that the evaluating system can take a global analysis of simplification error by considering both the geometrical and the geographical feature, the result is significant enough for different needs. This error evaluating system for simplification algorithms can be useful references for automated cartographic generalization and contour generalization study.