Research Of Key Technologies About Spherical Terrain Rendering And Roaming Based On External Memory And Network

In recent years, global-based three dimensional terrain roaming system has been deeply concerned by many people and widely used in geographic information systems(GIS), the field of military defense, and urban planning and so on. However, with the enhancement of data collecting capability and improvement of the people’s requirements for quality, the global-based three dimensional terrain rendering system has to deal with dozens or hundreds of GB datas, and even more than 1TB datas. So, how to render large-scale spherical terrain in real-time under limited computer hardware conditions became current research hotspot.This thesis focuses on the organization and schedule of spherical terrain data and spherical terrain roaming techniques. The main contributions of this work include the following aspects:(1)Study some techiniques about spherical terrain data organization in-depth. Design a quadtree-based multi-resolution terrain model for spherical terrain and the corresponding terrain block encoding scheme; after comparing the advantages and disadvantages of the two methods of data storage and management, this paper decides to select file system to store and manage terrain data; combining terrain block data to optimize the data organization and reduce data I/O time, and take advantage of the special condition of the spherical terrain elevation data and exclude some part of elevation data, which reduces the amount of data that need to be processed.(2) Study some techiniques about spherical terrain data schedule in-depth. Proposed an new improved View-Frustum Culling technology for spherical terrain which based on the View-Frustum Culling technology for flat terrain; after considering both the effect of drawing and rendering efficiency, designed a method for roughly estimating the projected area of the node to do node error evaluation, and realized the node traversal and update algorithm for multi-resolution spherical terrain; proposed two terrain rendering accelerating methods: data-prefetching and multi-threaded data scheduling techniques; what’s more, in order to enhance the scope of application of the spherical terrain rendering system, this paper designed a data scheduling scheme combining local external memory and network server.(3) Do research into spherical terrain roaming. Including sight translation, translation along spherical surface, normal rotation of the spherical terrain, accelerated rotation of the spherical terrain, the sight tracking and location tracking of observing objects, and several kinds of transient mode of switching viewpoint and so on.