Researches On The Surface Modeling And The Accuracy Evaluation Of DEM

Digital Elevation Model is a kind of discrete digital expression to the terrain relief of the earth surface. As the most important spatial information in geographical database, DEM plays a more and more important role in many area, such as GIS, RS, VR, digital battlefield and so on. In the research of DEM, its accuracy influences the users and producers, hence people always hope DEM can reflect the fluctuantion of the earth surface exactly and objectively. Therefore, the accuracy of DEM becomes one of the DEM research hotspot, and it's very important in theoretics and valuable in use.This paper carried on the researches to the surface models of DEM and the accuracy of DEM evaluation, especially put forward a new kind of smooth surface model based on Triangular Irreglar Network (TIN) and a new kind of index to estimate the accuracy of DEM. The main results are as follow:(1) Systematically discussed the methods that built up the DEM by the contour line, we put forward new algorithms of auto-adding characteristic points that eliminated the "plane triangle" in constructing TIN and approximating important characteristic points by Lagrange interpolation polynomial. Testing in terrain relief, and the algorithms can optimize the structure of TIN nicely.(2) According to the smoothness of the terrain and correlation between adjacency data points, the paper studied the possibility of smooth surface constructing of DEM based on TIN. Then based on Tayor fomula, vertical normal vector, triangular decomposition, continuous and smooth of surface and so on, a new kind of interpolate model of DEM was proposed based on TIN. We also made a visualize analysis of the model.(3) Comparing some corresponding algorithms based on points and considering the efficiency, we put forward a new algorithm of contour trailling based on line segment, then designed and carried out the reconstruction of the contours from Grid and TIN. The algorithm had high computing efficiency and controllable selecting accuracy.(4) Put forward a new kind of index which is the ratio of areas between the original contour and the reconstructed one to the length of original contour to estimate the accuracy of DEM. By rasterizing contours and reconstructing contours, we estimated the accuracy of DEM, then evaluated the degree of the DEM was consistent with the terrain relief.(5) According to the theories and methods in the paper, by Visual C++ 6.0, we carried out modeling DEM, interpolation models constructing, reconstruction of the contour line and estimation to the accuracy of DEM and so on.