Key Technology Of 3 D Digital Earth Building

Nowadays, users ask for computer applications to give more innovative virtual sense of reality and friendly man-machine interaction, In addition, The graphics hardware acceleration techniques and the researches on computer graphics promote the development of the concept of Digital Earth. By3D rendering technique, showing a high-reality, high-resolution Virtual Earth that allows user to roaming in the scene and make spatial analysis becomes true. But the current researches always focus on digital terrain visualization in small-scale outdoor scenes and the enhancement of rendering rate of algorithm. The approach of building Digital Earth with massive global elevation is still improved. In the thesis, with the results of previous studies I explore some innovation and make some distinctive achievements.In the beginning, I summarized the characteristics and techniques of well known foreign digital earth systems, and analyze the key techniques of building3D digital Earth. By different collection methods, the digital elevation model is different. Introduce how to get terrain elevation data and texture data by software synthesis methods, as well as the construction algorithm of terrain multi-resolution grid based on the LOD.The infrastructure of global digital terrain rendering is the organization of geographic information. Take the pyramid model to split the global elevation data into tiles. The low-redundancy storage of level of detail mechanism is in effect to achieve the aim of multi-resolution hierarchical structure within the tiles. In order to reduce the computational burden of the rendering process, the loss of static error in the terrain tiles is calculated in the pre-procession and stored in the file. Then pre-process the global texture image data in the same way.According to the needs of real-time visualization rendering, pre-selecting and multi-threaded scheduling DEM data is important. Both Spherical terrain and near-earth flat terrain data are pre-loaded by different way. When the camera is out off a certain long distance, only schedule the textures of spherical model, but not the elevation data. The thesis highlights the dynamic scheduling schemes which relates to the line of sight and movement trends in the flat terrain. By the urgent rendering needs of each tile, set different scheduling priority to each tiles, and then use the technique of multi-threaded parallel process to load/unload level of detail.Make a mathematical model of the3D digital earth. I designed a visual error evaluation system to distinguish and constraints which level of detail the mesh should be split. Repair the cracks at the edges of tiles which are caused by different resolution in adjacent terrain tiles. Solve the sudden jump in the adjacent resolution dynamic conversion. At the end of the thesis, I designed and implemented the main framework of the3D digital earth system, and described the structure of each module.