| With the raising of Digital Earth, there has been great improvement in Digital City in recent years. GIS (Geography Information System) , as the platform of spatial information processing , supports both Digital Earth and Digital City greatly. The spatial data related to Digital Earth is multi-dimension, that make a demand of abilities of GIS to tackle them, so 3DGIS has been an important direction currently during the development of GIS. Visualization is the intrinsic character of GIS. It means the integration of information and provides a three-dimensional environment for people to learn the world. The efficiency and the quality of visualization have an impact on the state and the deepness of learning. So it is no doubt to pursuing the high-level visualization for 3DGIS. However, Digital Earth involves many complicated objects and covers huge number of data. So it is a great challenge for 3DGIS that how to construct a visualized environment to show this numerous and jumbled scene.The numerousness of the object surely asks for the capability of processing the great number of data during the visualization, keeping high fidelity of the scene in the same time. Obviously, the traditional visualization way of GIS can do nothing with it, we need to introduce some new theory and technique.As for the visualization of scene of huge number of data, we should try from two ways: one is reducing the "unnecessary" data, which can be done by studying to cut down the "redundancy" in the expression of the model of the visualized objects. It is embodied as the studying of model simplification; another is increasing the quantity of information expression in unit time in course of visualization, which can be done by studying to enhance the visualization efficiency that is to accelerating the render. It is the method exchanging the space with the time, which included both the software and the hardware reason of visualization speedup.Starting from those two points, based on the former research, this paper try to make further improvement of the technique of model simplification to the visualized spatial__________________________________________Abstractobjects. Aiming at terrain simplification, we advance a rule of model simplification giving attention to both the character of nature and the user-defined properties, which is based on the quad-tree. And simultaneously, we combine the triangle binary-tree with the quad-tree, managing to resolve the crack during triangularization. As for the visualization of the vegetation such as the tree, this paper suggest an expression way with the LOD model, which composed of three levels: line-draw model, billboard model and symbolized model. It can greatly reduce the volume of datum. The search of spatial data is an important course that will affect scene rendering. The R-tree is a commonly used index structure of spatial data. After pointing out the insufficiency in the former research, a new R-tree and algorithm were built. In the test, it is proved to make great improvement in search efficiency.Being the physical basis of visualization, the extent of hardware utility works on the scene-rendering directly. This paper studied how to make full use of the resource in certain hardware condition, to exert its accelerating function. It was proved by experiments.To acquire a real and reductive world is the target of visualization of scene, and this is also a theme can't be discarded during research. The third dimension of the scene depends on the render of illumination. This paper compare the Phong illumination model with the BRDF illumination model, and study how to import the Multi-angular Remote Sensing Data into the practical BRDF illumination model. Finally, associating with Project 863, taking Digital Zibo as an example, this paper develop a practical kernel component of three-dimensional visualization based on OpenGL, and realize a network-based visualization experimental system. It can make scanning of large-region scene.
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