The Study Of Contour Generalization Based Upon Multiresolution DEM Model

The multi-scale expression of spatial data and map automatic generalization as one of the key questions of GIS utilization has been the great difficult problem of GIS and cartographic generalization all the time. The construction of seamless and non-scale map database is a development trend of the map database in the future, and is also a great challenge for the automatic generalization domain as well. What constitutes the key problem of automatic generalization research under the environment of GIS is the reality of having big-scale database as the data source, using generalization methods, and carrying on automatic increase and decrease to geo-spatial object's value so as to get spatial information varying with scale change.The automatic generalization of relief form is ever the relatively difficult work of data processing and analysis in generalization domain, in the study of this problem, the present methods are adopting the method with groups of contours generalization which takes into account the geo-structure lines, theprogressive approach to generalization and the fractal method etc. These methods have some restrictions in the profundity of research and aspect of practicality because of contours' special relations and the complexity of the relief form.DEM is the most important spatial material and key data according to which the relief is analyzed in GIS geographical database. The Technique of multi-scale DEM is based on model and algorithm, and it can be realized through reducing quantity of triangle and changing the size of grid to display and simplify DEM of different scale. The DEM derives from contour data and vice verse, the contour data derives from the DEM, so the scale of relief map is consistent with the resolution of DEM. The thesis has put forward a method of surface generalization suited for automatic generalization of relief form, which adopts the way of simplifying DEM and produces the contour of the target scale on the basis of the analysis of geo-structure information. At the same time, the author has carried on some perfection on the algorithm and accordingly proposed a series of feasible methods for the question in the process of generalization. As a result of that, the aim to realize the generalization of contours on the basis of simplifying DEM in this research has been obtained.The main content of this thesis is as follows: 1) On the basis of systematic analysis about the concept of automatic generalization, the research background and the demandof application, the author has summarized the characteristics and demand of map generalization under the digital environment and GIS environment, and has summed up the present method of contour generalization.2) Through the comparison of the two kinds of construction topographical level models which are respectively based on the GRID and TIN, the thesis has adopted the method of deleting vertex of TIN to simplify DEM and has realized this course.3 ) The thesis has put forward a surface comprehensive method introducing the producing background of this method, the procedure of application and its characteristic, then this method is tested by adopting the simplification model of the most independent points aggregate, based upon which the comprehensive result has been analyzed and compared.4) The author has adopted different experiment environments to carry on verification and appraisal in many aspects to this kind of method, and examined the error qualitatively and quantitatively to the experimental result under different situations, and drawn some conclusions.The research in this thesis is the exploration and practice of a new method in the field of generalization, which can help obtain the purpose of generalization. It proves to be an innovative way in the realization of relief form generalization.