Data Organization And Fast Display Based On Global DEM Terrain And Objective Models

The Visualization Research of 3D Terrain is an important part of Virtual battlefield environment, Geographic Information System(GIS),Digital Photographing(DP) and Remote Sensing System(RS).It is a subject mainly research on Digital Terrain Model(DTM) or the simplification, display and simulation of Digital Elevation Terrain ,it is a subject of Computer Graphics. But the current theory and method mainly process the visualization of single block, it is hard to realize the visualization of large scale data. The real-time display of large scale data terrain is the hard work of many scientific fields, and is an important part of the virtual battlefield environment.In this paper,data organization and fast display of global DEM terrain are discussed. To realize real-time walk-through of global DEM terrain, it firstly analyzes the basic character of DEM data organization, by building global DEM terrain multi resolution model with quad-tree data structure , view port related visibility judgment and dynamic scheduling strategy realizes global data seamless walk-through based on eliminating fraction the caused by different resolution terrain putting together. Last, because all kinds of building and arm equipment are needed in virtual battlefield environment, the ground object modeling and display are partially discussed in the end. All the research work is list below:(l)Blocking global DEM terrain, first separates earth into east and west hemisphere, then separates every node into four nodes. Each node represents one DEM data block. According this separation, by quad-tree data structure can get global different resolution DEM data storage architecture. This tree structure has merits listed below compared with others:(a)satisfies the need of display, if the view distance is different, the visible area and visibility precision is different. Different resolution organization can improve display rate.(b) extension is easy. High resolution DEM data can add at any moment without effecting tree structure.(2) In order to improve graphic display rate, view port related visibility judgment algorithm is introduced. If visual effect can not be affected, can choose appropriate data representation according to current vision field of operator. Can choose different detail layer according to different terrain that is the near and changed greatly area can use high detail layer and far area use low detail layer.(3) In the simplification algorithm based quad-tree structure, because of using different detail model, if two neighboring area have different detail, the high detail block have more nodes and more elevation information than the another block. The fissure will occur if they share the same boundary. By modifying the connection of boundary node, eliminating the fissure that probably occur, realizes the seamless walk-through.(4)Using dynamic scheduling strategy. The dates in buffer are partly changed or changed none when view port is changed. At one respect deletes data that moved out of visible area and adds data that moved in, at the other respect visible area data also need to be updated because of the changing resolution.(5)At the respects of graphics display, naturalness and sense of reality of battlefield , environment is enhanced by adding texture and lighting.(6)Building multi-detail level model for ground object, choose different detail model to display according to different view distance.The content of this thesis is a part of national 863 project named "Research on techniques of virtual battlefield environment based on space-based comprehensive information". It realizes the seamless walk-through and real-time display of global data in the virtual battlefield environment by efficiently build terrain data.