Data Organization And Scheduling For Accelerating Rendering Of 3D Geographical Scene And Time-sequential Multi-screen Synchronous Roaming Technique

Geographical scenes, especially natural geographical scenes usually are characterized as large scale, highly complex, time-sequential dynamic and strongly interactive. Natural geographical scene contains many natural and man-made elements. Among these elements, the most fundamental and important factor is terrain. Because of the large amount of terrain data and terrain surface texture data, it is difficult to realize 3D real-time visualization or rendering. At present, most of the 3D GIS software need to be improved in the aspect of supporting massive data. Therefore, rapid 3D visualization of massive data in real time becomes one of the key problems in 3D GIS and virtual geographical environment study. In addition, in view of the temporal dynamic feature of the natural geographical scene, the rendering of 3D geographical scene needs to express not only a certain stage of the geographical environment, but also the dynamic changes of time-sequential or the evolution process of geographic system. Traditional single computer single-screen display method usually fails to meet the application requirements of user immersion, large field of view, and high-resolution visualization. Using virtual forest environment as an example, this paper studies the data organization and scheduling for accelerating rendering of 3D geographical scene and time-sequential multi-screen display technique. The main contents and results are as follows:(1) On the theory and methodology, the advantages and disadvantages of the current technologies are analyzed:the large-scale terrain simplification technology, photo-realistic texture mapping technology, organization and scheduling strategy of massive terrain data. We put forward the ideas and technology roadmap to realize rapid rendering of massive terrain data based on the data organization scheduling and optimization strategy. The modeling methods of terrain, vegetation and buildings are introduced in detail. Based on these methods, we discuss scene graph and Spatial hierarchical division methods for building virtual 3D geographical scenes, and summarize the applicable theories of visibility culling, multi-threaded data scheduling, level of detail (lod) simplified model based on quadtree, and data cache mechanism.(2) In data preprocess, a view-independent, multi-resolution terrain and texture data model is built, and the technology of massive terrain and texture data preprocessing based on data slicing is designed and implemented. This technology can reduce the time for data processing in real-time rendering process and the computation cost of the computer, thus improve the rendering efficiency of large-scale complex 3D geographical scene.(3) In terms of data organization, scheduling and optimization strategy, we put forward a multi-threaded mechanism to improve the scheduling efficiency of scene data and the fluency of scene rendering. The scene rendering thread as created as the main thread and data scheduling thread as child thread. Based on the mechanism, multistage cache and fixed memory buffer pool strategies are implemented. These help reduce the scheduling frequency between internal and external storage data and the number of memory allocation and unload. The tests show that applying the strategy and optimized processing, the frame rate of scene rendering can be maintained at 60 FPS, while not subject to limits on the amount of data.(4) In regard to the multi-screen synchronous display technology and the design and realization of a scene roaming system, we utilize multi-screen display technology and Cardial difference method to generate a roaming path, then integrate the results into a 3D information system which is capable of synthesizing and managing forest landscape. A time-sequential forest scene visualization roaming system which is based on a computer with multiple screens is implemented, with embedded player functionality of real picture and output functionality of 3D geographic scene. The system has been used in the achievements demonstration of water loss and soil erosion control and treatment in ChangTing County, Fujian Province, and the performance is satisfactory and well received.