Large-scale Raster Topographic Map Vector Algorithm And Realization

Geographic information digitalization is one of key tasks in Geographic Information System development, which takes about two thirds of the whole workload in GIS. Involving several subjects, vectorization of topographic map is a challenging technique with theoretical and practical values in digital maps productivity remarkably. Previous theories and applications have provided solid basis for further research, but there are still some urgent and thorny problems available. Especially to large-scale topographic map, some problems need to further research. Firstly recent developments in vectorization are analyzed, and some problems in these researches are pointed out. Secondly, an analysis of several typical vectorization methods is made and some ideas and algorithms about point symbols extracting and line tracking are put forward. At last ,a proposed methods are performed under the environment of AutoCAD with Visual C++.NET, ObjectARX and IESDK.Main contributions of the dissertation include:1. A thorough research on the available methods and techniques of vectorization is performed. Based on the comprehensive analysis of recent developments in this field, main problems in the research are pointed out.2. Several typical vectorization methods is analyzed and compared, which enable a judicious decision while selecting a vectorization algorithm for topographic map.3. By analyzing automatic recognition of point symbols, an interactive vectorization method to point symbols is realized.4. Based on sparse pixel based methods, a new algorithm is put forward. The algorithm not only inherits the advantage of sparse pixel based methods, but also repairs its shortage.5. Based on the thoughts and algorithms proposed above, a prototype system of semiautomatic vectorization in AutoCAD platform is developed.