Research On Key Technologies In Global Virtual Geographic Environment Construction

With the strategy of Digital Earth proposed and implemented, construction of global virtual geographic environment base platform has become an urgent problem for the national security, land and resources management, urban planning, agriculture and forestry applications, crisis management, disaster monitoring and other large-scale application fields. However, with the rapid development of the remote sensing technology and space technology, more and more sources of geographic data make the amount of data increasing geometrically. How to efficiently handle, organize and distribute global-scale rapidly increasing massive multi-sources spatial data and achieve realistic, smooth, real-time 3D visualization becomes an urgent issue to be further solved. Meanwhile, since three-dimensional geographical environment has been used widely, more and more users are not satisfied with just simplely 3D visualization of variety information. It is an urgent requirement that geographic spatial analysis of non-specific areas of the global scale as well as decision-support.In order to solve the problems above, this paper focuses on the key technologies in virtual geographic environment construction which consists of global massive raster information processing, organization and distribution, multi-scale vector data organization and environmental enhancement, global topography mapping and efficient rendering, geographic analysis model construction and visualization, etc. Specifically, the main contributions of this thesis include the followings:●A parallel processing based global multi-scale raster data organization and distribution method is proposed.To solve the problems including efficient processing, organizing, scheduling and data sharing for multi-application service of global multi-resolution raster data, a parallel wavelet processing and ordered quadtree structure based global raster data pyramid model construction method is proposed. Global data consistency coding rules and hierarchy scheduling mechanism which can be mapped to the machine-bit computing are designed to improve the scheduling efficiency of massive data. In order to improve the efficiency of mass data preprocessing, the property of parallelism of wavelet algorithm and the data transfer mechanism between multi-processor logical topology are analyzed, and the multi-resolution model construction method based on multi-processor parallel processing method is proposed. In order to improve the global raster data general service capabilities, an on-demand services massive raster data management and distribution engine is designed, the expandable coherent data distribution interface is built, and the problem of heterogeneous multi client systems concurrent access is resolved.●A multi-resolution vector data modeling, organizations, and 3D visualization method is proposed.A vector static multi-resolution hierarchy construction method based on data reduction and hierarchy blocking and a vector dynamic multi-resolution hierarchy construction and scheduling method based on viewpoint changing and screen error metric are proposed. By these two multi-resolution models vector simplify problem is resolved and achieving smooth transition when zooming the scene. These methods can resolve conflict between massive vector data and limited capability of computer process to meet the requirement of real-time rendering of large-scale vector data 3D visualization. On the seamless integration of vector data and 3D terrain in visualization, combined with the ground objects characteristics vector represented, two kinds of terrain matching methods such as features adjusting and terrain adjusting are proposed. These methods further enhance the visualization effect of vector data.●A GPU-based real-time rendering algorithm for global massive terrain data is proposed.On the features of massive terrain features, to fully excavate the GPU high-speed parallel rendering capabilities, a center deviation Geometry Clipmap algorithm is proposed. The algorithm combined with the global multi-resolution pyramid raster data model, using incremental texture updating technology and Geometry Instancing techniques to further enhance terrain rendering speed. Most of the calculation processes are transfered to GPU to reduce CPU computing pressure. So it can meet the large-scale terrain visualization real-time rendering requirements. On the characteristics of the global terrain mapping, we fully consider the effects of earth curvature and topographic relief, introduce concept of the distance factor and modify traditional visibility culling method to further reduce the rendering burden of massive data and then improve system efficiency and response speed of rendering.●Two kinds of typical geography analysis models and visualization methods are proposed.To enhance the assistant analysis and decision-supporting capabilities of the virtual geographic environment platform for crisis management, disaster monitoring and other applications of the typical requirements, a flood routing model based on the volume method and the recursive search algorithm are proposed. This model can realize searching calculation of flood connected region and flood dynamic rooting behavior visualization in the space. A radioactive nuclides diffusion model based on improved RIMPUFF algorithm is proposed, considering the wind field, dry deposition and radioactive decay of radionuclides and other factors. It can implement dynamic visualization analysis of radionuclide diffusion process on complex terrain and complex environmental conditions.●A prototype of the global large-scale virtual geographic environment system-GVGE is designed and implemented. Integrated the front related research and practice algorithms, a scalable visualization analysis capable globe-scale virtual geographic environment system GVGE is constructed. The system is not only an experimental system integrated research results, but also an application platform supporting various scene data organization and management, which can interact with complex scenes on a large scale roaming on a variety of ways. Moreover, as an important base platform of the virtual battlefield environment, this system has been applied in many related projects.