| Digital earth is integrated by WWW, Simulation , Virtual Reality and other modern technology such as the Remote Sensing tightly . Its character is that a lot of datum is embedded in it. At a sense of 3D,it describe our earth with LOD, namely, Virtual earth. As a core part of the truss about digital earth, the visualization of 3D terrain sight is attended intensely. Nevertheless, the designing of space data model and operation about GIS is oriented to 2D plane structure. In fact, it has not really ability of disposing 3D datum. Most national software about GIS is still developed at the base of mature 2D GIS product and its ability of disposing datum is limited. Thus, many applications about GIS is restricted too. For example, there are many problems such as the layout of subterranean duct and the designing and layout aimed at military affairs and so on. In order to resolve them, the information about elevation is necessary. With the improvement of the ability and measures of obtaining digital space datum and the application of GIS in variety of fields, people are not content to 2D sight and begin to create real 3D geography scene with space datum such as GRID datum, Vector datum used to romance paths and lakes, aviation photograph and real scene photograph. The thesis explore many difficult problems of the research of current 3D-GIS.At the direction of digital earth and the idea of oriented-object, it create the earth's surface model based on global datum with GTOPO30(Global DEM). The data structure accords with people's normal thinking and makes for the space analysis and show of 3D space object. In the thesis, these key techniques is implemented as follows: The ability of disposing datum based on local terrain. It sustain the format of both GRID and TIN and the transformation between them. In general, DTM is denoted by the format of GRID and TIN. The advantage of the former shows variety of elevation in detail sufficiently. Its relation is simple and arithmetic is realized easily. It is convenient to manipulate some space datum.. Of course, there is some shortcoming. It is out of line between the anomalistic ground feature and the inerratic. The shortcoming can be resolved by TIN format datum., but it can bring some new problems such as the complexity of arithmetic. Because the thesis researches global datum, GRID format that adapt to terrain in great force is used. For TIN format, it must be transformed into GRID format. The unified layout and management about global DEM. It restores a great deal of datum in the way of object and manage GB grade datum with the measure of both area and block. The conventional storage way based on chart layer is not adopted. It brings about the agility and expansibility for the system..It deoxidizes the 2D plane DEM into real 3D space DEM on the earth ellipse sphere with the measure of bent plane draft based distance entropy. The radius of parallel circle gets shorter and shorter, so when the DEM data is deoxidized on the earth ,the precision of the scale is different. The article discuss the problem and put forward a settling scheme.The technique of Automatic recognition about data block. It searches and distills the datum that is used in the current scene rapidly and bring to bear the polygon clip arithmetic skillfully. The thesis realizes the global ramble without boundary and put together these data blocks without gap. It doesn't adopt the RUP that drives by Use Case, but brings forward the new software development pattern that drives by both concept model and Use Case model at the aid of field experts.It realizes the visualization of 3D terrain scene with the technique of OpenGL and VC++ based on the .NET. In addition, it includes 3D shade terrain, triangle net terrain, real time terrain scene ramble based on LOD, fa?ade texture, zooming and fowl look and so on.The realization about transformation between different data format. Because of the different background of data, there is a problem about striding the flat roof. When we restore multibyte datu...
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