Research Of Network3D GIS Critical Terrain Data Extraction And Reduction Method Based On DEM

Display of geographic information system has begun transforming fromtwo-dimensional symbols to three-dimensional graphics. The three-dimensionalgeographic information system can analysis and manage the space data. The system can beable to simulate the human perspective, analysis, management, as well as present realthings in the space. It brings a variety of interactive among more realistic simulation of thethree-dimensional world. However, Network of three-dimensional geographic informationsystem not only contains the symbols which describe geographic information, alsoinvolves multitude of description of geographic information raster data. Three-dimensionalterrain data is the basis of showing geographic information. Therefore, three-dimensionalterrain data transmission has become a critical problem in the network ofthree-dimensional geographic information system.Through the research of model simplification technology based on grid, we can findthat here are some of critical data points which are play an important role in meshsimplification. Therefore, the model simplification thinking is applied to the datatransmission of the three-dimensional. That means extracting the critical points and thentransporting to the client, recovering three-dimensional terrain data in the client, and thencreating a three-dimensional model. Therefore, how to extract the critical terrain datapoints is studies in this paper, and approximately restoring three-dimensional terrain dataaccording to these data points and generating the tree-dimensional terrain data.Critical terrain data points contains terrain feature points such as the peak, valleypoint, ridge point, depression point, saddle point which can descript the terrain feature inthree-dimensional terrain model, and also contains the important topography data pointswhich have a greater impact on the topography. We use the slope and curvature method toextracted terrain feature points. We use the typical methods which are based on slope andchange of slope to extract the terrain points which have a great impact on terrain change.The typical methods are the maximum gradient of the algorithm and the difference algorithm. This paper also discussed and analyzed the difference between the twoalgorithms.The DEM described three-dimensional terrain data is the regular grid data, so theclient needs to use interpolation algorithm to calculate elevation of grid data points whichare not be extracted. With the interpolation calculation we can restore thethree-dimensional terrain data, and then establish three-dimensional terrain model. Sincewe use the above series of methods to extract the critical terrain data and restore to theoriginal terrain data are detrimental, it needs error analysis based on restore terrain data.Finally, the system passed on the test and verified the feasibility of the method.