| Scale is the space or time unit used for study of a geographical object or a geographical phenomenon. It also refers to the scope and the frequency of the phenomenon or process involved in space or time domain. In brief, it is the description of the relative size of the object in its container. Scale is the foundational issue that should be studied in geographic information science and cartography, remote sensing science, geography, hydrology and other disciplines.In any aspect of the process of cognition, acquisition, modeling, measurement, visualization, storage, and transmission of geographic information, phenomenon and process, scale is inseparable from the discussion. As the application field of geographic information science is expanding and the society requirements is increasing. Especially under the digital environment, on the one hand, the spatial data acquired is huge; on the other hand, people have high expectation for use of high-precision data at anytime and anywhere. This requires the digital terrain data to be able to efficiently transmit among a variety of media and be represented. In addition, for such a mass of data regardless of what kind of realistic visualization technology, it will be difficult for people to quickly and effectively mine the required knowledge. It has gone far beyond the scale scope of human brain cognitive. Therefore, using multi-scale theory and technology to observe, process, and analyze the geographic phenomenon in multiple levels, and describe geographic process become so important. The multi-scale processing and representation of spatial data has become the fundamental content in creating multi-space scale database and realizing multi-scale GIS or scale-free GIS or on the fly GIS, at the same time, building spatial data representation model dependent on scale and realizing multi-scale automatic generalization of geographic information is the key technology for processing and representing multi-scale spatial data.Scale and spatial scale theory is a hot research issue in geography, cartography and geographic information science, and these theories are on the basis of spatial cognition, information science, computational mathematics, computer graphics, as well as application.Based on the spatial scale theory of geographic information, this dissertation studies the mechanism of multi-scale phenomenon; summarizes present multi-scale and multi-resolution technologies and methods of spatial information. After analysing the connotation of DEM multi-scale representation in-depth, merging the important function of terrain characteristic lines and the basic idea of progressive map generalization, making use of wavelet multi-resolution analysis theory and the newest results of scale theory, a theoretical frame of progressive multi-scale representation for DEM is proposed and progressive multi-scale representation and automatic generalization of DEM is accomplished.The dissertation includes the following sections:1) The scientific significance and necessity of multi-scale processing of spatial data is discussed from the aspect of academic development and theoretical research of geographic information and social demands. The research general goal, main research content and the organization of dissertation is given.2) Related works. Analyzes the research content and the present results of spatial scale, introduces the researching topics and development status at home and abroad in the area of spatial data multi-scale processing and representation. It systematically analyzes and summarizes relevant researching results and existing problems of spatial scale, scale type and scale transform methods in DEM digital terrain analysis. It mainly analyzes scale characteristics of geographic space to provide goal and technical direction for further research.3) Research on the multi-scale representation model based on progressive generalization. It analyzes the inefficiency of current spatial database, studies the basic idea and its formal description of progressive map generalization, and points out that progressive idea is an effective method to set up multi-scale vertical connection relationship. Combining with the scale characteristics of geographic space, it puts forward and studies the multi-scale representation model based on progressive generalization so that there is analyzing, processing and expressing ability of scale-dimension when dealing with DEM data.4) Study on the reasoning of terrain characteristic lines. First of all, it sets up constrained Delaunay triangulation (CDT) and a hierarchy structure of contour lines, and realizes terrain classification and adjustment of the trend of contours. Then it extracts the flat triangle regions from CDT, and extracts general terrain characteristic lines from each flat region. Conduct weighting interpolation on the elevation value of each point in the terrain characteristic lines according to certain algorithms and achieve characteristic lines more in line with the actual terrain. Add the terrain characteristic lines into TIN to amend the flat triangle region. And then the method of extracting terrain characteristic lines from group contours is proposed:Firstly, Constrained Delaunay Triangulation of contours is constructed; secondly, the turn angle, curvature and shape index values of each vertex on the contour are calculated, and the candidate terrain characteristic points are classified by the given threshold; thirdly, connect the points matching conditions into terrain characteristic lines according to corresponding principles; fourthly, the line is optimized. Compute the flow direction of each triangle in Constrained Delaunay Triangulation based on contours, and classify the public sides of Constrained Delaunay triangle according to the combination relationship between various flow directions. Finally, the algorithm connecting the related sides to obtain terrain characteristic lines is proposed in dissertation.5) The multi-scale processing model of spatial data based on wavelet analysis theory. It briefly introduces the basic principle of wavelet analysis theory, analyzes the possibility and necessity of using wavelet analysis theory in processing and representing multi-scale spatial data. It analyzes the principle and model of multi-scale processing and representation of spatial data from the application aspect of wavelet analysis theory. Based on wavelet analysis theory, it proposes multi-scale processing model of spatial data that meets the requirements of and matches scale-dependent spatial data model. It realizes multi-scale representation model based on binary and multi numbering system, and makes experimental analysis. It also studies the multi-scale representation model and implementation principle based on lifting transform, and does comparison with former methods.6) Based on the improved extracting algorithm of terrain characteristic lines, terrain characteristic lines based on multi-scale DEM are extracted and the reasonableness of the method proposed in this dissertation is verified by the overlap rate of terrain characteristic lines.At last, a comprehensive conclusion is summed up and the research directions and problems to be solved in future are pointed out in the paper. |
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