The Study On DEM Scaling Based On The Wavelet Theory

In recent years, the Digital Elevation Model(DEM) has obtained widespread applications in many fields, such as Geographic Information System(GIS), Remote Sensing(RS), hydrology and so on. In the course of the application of DEM data to analyze such as topographic features, the fine spatial patterns and macroscale characteristics are both needed. However, in most instances, this is very difficult to be achieved using single resolution files considering the large quantity of data. It is very necessary to implement multi-scale representation of DEM data effectively with high precision and main characteristics.Based on generating hydrologically correct DEM of large-scale using ANUDEM software in the research, the wavelet multi-resolution anlysis (MRA) and the square root model were applied to transform DEM of large-scale for exploring the changing law of all kinds of topographic indexes in map generalization and providing a way for the data resource of lower resolution DEM. Meanwhile, there is reference significance to the automatic generalization of topographic map.Firstly, the research was conducted to generate hydrologically correct DEM of large-scale in the undulated hilly region in Northeast China and in steepy hilly region in Southern China with the 1:10,000 digital topographic maps, including contours, spot heights, streams and lakes, and using the ANUDEM software. The derived contours, the representation of topography, river networks and DEM RMSE were selected to evaluate the quality of the DEM. Result showed that using digital map and ANUDEM software can generate hydrologically correct DEM of large-scale in these two sample regions. For generating the DEM, three main parameters of ANUDEM including resolution, iteration number and 2nd roughness, were 1m, 40, and 0.5 in the undulated hilly region in Northeast China and 5m, 40 and 0.6 in the steepy hilly region in Southern China. The DEM RMSE reached the DEM precise standard of classâ…¢of USGS. The derived contours, and river networks were highly up to the input data. The DEM generated can correctly describe the topography characteristics and the relationship of physiognomy and hydrology and provide data support for the simulation of hydrology and soil erosion.Secondly, the Wavelet Multi-resolution Analysis and Square Root Model were combined to simulate the general process of DEM by setting the scale parameters. The DEM was generated using the 1:10,000 digital topographic maps and ANUDEM software in the Xiannangou Cachment which is a typical catchment within the Loess Hilly and Gully region of Loess Plateau. The study was to explore the effect of MRA of DEM on the topographic factors, including slope, curvature and river networks, and their changing law with the change of special scale. Meanwhile, the quality of generalized DEM was appraised by terrain comprehensive characteristics analysis, comparison of contours and terrain factors, including slope, profile curvature and river network, the DEM of 1:50,000 topography map as reference. And selecting the appropriate scale parameters to match the DEM properties of 1:50,000 toograthy map. Results showed that the generalized DEM almost reached the Chinese secondary standard of DEM precision. In the course of Wavelet Multi-resolution Analysis, the slope, profile curvature and cotours was increasingly smoothing with generating DEM of the smaller scale parameters. The DEM properties of 1:125,000 scale parameters was similar to 1:50,000 topography map from the slope and curvature frequency curve, features of contours and river networks. Results showed that the generalization of High resolution DEM obtained expected effect of the automated generalization of DEM using Wavelet Multi-resolution Analysis and Square Root Model. The result of study provided a new way for the resource of DEM data in the model of hydrology and soil erosion.