The Study Of Topographical Sketch Based On DEM

Terrain sketch is a picture and method of geomorphology,terrain structure and internal mechanism reflectance by drawing lines,which is based on the knowledge,analysis and generalization of geographical environment.It is deeper impressive and more authentic than photograph which is just simple copy of the real environment.With the development of computer technology and digitalization,the absence of terrain cognition was brought by quantitative and digital expression of terrain.Terrain sketch has the advantages of simple,abstract,and impressive in terrain express.But it is difficult to inherit due to the painting skills needed.Therefore,we proposed a terrain sketch painting technology based on DEM data with computer.The main research and results which was included in this study are as follows:(1)Automatic extraction of terrain characteristic features for terrain sketch.The typical terrain and topology characteristics were displayed on terrain sketch by using feature lines from the analysis on terrain.The feature lines of loess landform includes visual contour line,shoulder line,young gully and the boundary line of loess tableland.The extraction method of each terrain characteristic feature has been tested.The stream line on slope was also extracted by designed algorithm to enhance the expression ability of young gully.The extraction method of shoulder line and terrace based on high resolution DEM has also been designed in this study.(2)Division of visual level considering perspective law and generation of terrain features in distant area.According to the painting skill of traditional terrain sketch,it is necessary to divide visual area to several levels.The division method in previous research has some problems like parameter non-adaptation and discontinuity of results.A new method of visual level division method has been proposed in this study.Two parameters in this method have also been discussed,and solved the parameter non-adaptation.The arrangement of terrain characteristics features has been implemented.An issue about gathering visual contour lines in distant area while drawing terrain sketch has been found.We improved the previous method and proposed an area-based generate method to decrease the contour lines in distant area.By comparing to the generation results of Douglas-Peucker algorithm,this method have advantages of better visual effect and threshold self-adaptation.(3)Framing and composition of terrain sketch in computer considering aesthetic.This study summarized the principles of framing and composition in traditional terrain sketch,concluded the specialties,principles and influence factors of terrain sketch artistry which was painted by computer(semi-)automatically.The most important influence factors,viewing distance and viewing angle,were discussed in this study.The method of statistical certain value has been proposed and the optimum range of distance and angle has been given in Yijun and Suide sample areas.A questionnaire survey has been done to evaluate the scientificity and aesthetic of terrain sketch painted by computer using the technology in this study.Survey result showed the rationality of terrain sketch painting technology including terrain features extraction,visual level division,generation of visual contour lines and method of optimum viewing distance and angle setting.The terrain sketch painted by computer has much scientificity and aesthetic by comparing to traditional terrain sketch.But it was still far from perfect and need to be improve.(4)Prototype system of(semi-)automatic painting terrain sketch based on DEM data with GISThis prototype system was coded with GIS based on technology of this study.It makes it possible to paint terrain sketch by using this system with interaction.