Multi-scale Three-dimensional Disaster Scene Dynamic Plot Construction And Key Technology Research

Earthquake emergency and rescue has great significance since the earthquake still cannot be accurately forecast. With the rapid development of hi-tech such as the spatial information technology, it has been an inevitable trend to use these technologies to assit earthquake emergency and rescue. Virtual earthquake scene can provide an intuitive visualization platform for deccision makers, due to the particularity of earthquake emergency and rescue, higher requirements are put forward for the construction of the multi-scale virtual disaster scene, as well as the effective use of the virtual disaster scene. To meet the application requirement of earthquake emergency and rescue, this paper researches the visualization of large-scale terrain, dynamic update of local earthquake scene, real-time terrain modification, dynamic plotting technology for earthquake disaster information expression, etc. The main work and contribution of this paper are shown as following:①A Virture Texture based large-sacale terrain dynamic scheduling and real-time rendering method is proposedTerrain is an important part for building the geographical environment of earthquake scene, it is the carrier for displaying other disaster information, thus the visualization of large-scale terrain is the basic for earthquake rescue. To solve the current large data transfer problem, this paper provides a dynamic scheduling and real-time rendering algorithm. This algorithm introduces the Virtual Texture technology, adopts the unified management framework for DEM(Digital Elevation Model) and DOM(Digital Orthophoto Map). With the real-time computing of GPU(Graphic Processing Unit) and dynamic analysis of CPU(Central Processing Unit), only the terrain tiles needed by the current rendering are loaded. These tiles are maintained and joined together into a cache texture in the CPU and then transfered to the GPU. The target tile and texture coordinates of the terrain grid points are calculated according to the tiles’ information in the GPU shader. This algorithm simplifies the data exchange and improves the memory management, it can effectively reduce the broadband expense, and has good performance for large data transmission. This algorithm are obviously beterr than the common method in the costs of broad-band, the frame rate and the implementation complexity.②A GPU tessellation based local terrain "Mosaic" algorithm is proposed The earthquake scene needs to be updated timely to show the latest situation of the disaster situation, therefore it should be able to dynamically load local high-precision terrain data. To ensure the accuracy of the updated area, this paper puts forward a GPU tessellation based "Mosaic" algorithm of local high precision terrain. Through the interpolation and subdivision on the terrain grid within the updated area in GPU to increase the number of triangles, the geometrical accuracy of the local terrain model is improved without increasing the bandwidth of the memory and video memory. This algorithm is obviously beterr than the common method in execution efficiency.③A photographic images based rapid updating method of local texture is proposedTo meet the dynamic texture updating of the earthquake scene, this paper puts forward a rapid updating method based on photographic images. To automatically register the photographic image with the coverage on the scene, this paper constructs the virtual camera frustum in the3D scene based on the internal and external parameters of camera, then get the coverage of the photographic images by calculating the intersection of virtual frustum and the ground, and finally update the local texture by multiple texture blending. This method overcomes the defects of remote sensing images such as data acquisition, processing and transmission, and simplifies the entire texture updating workflow and improves the timeliness of the texture updating. What’s more, high definition photographic images can provide more detailed geomorphic information, meeting the requirements of practical application.④A detail controllable terrain modification method is proposedEarthquake often causes a lot of terrain deformation, such as ground fissures, collapse, landslide, collapse, debris flow. These geological disasters pose a great threat to people’s life and property, effectively representation of these deformation in the3D scene has great significance in earthquake emergency and rescue. However, because of the acquisition of these deformation data is difficult and high cost, modeling the terrain deformation based on real data is unrealistic, so simulating the deformation through interavtive modification of terrain has realistic significance. However, most of the existing simulation platform is based on static terrain, and cannot express real-time terrain deformation. In view of this, this paper researches the real-time interactive modification of3D terrain, puts forward a workflow for interactive terrain modification and representation, Terrain modification is completed by GPU shaders, and the implementation efficiency and effect of modification are optimized by using "Ping-Pang" algorithm and batch processing; In addition, this paper introduces the multifractal algorithm to create a controllable random disturbance on the deformation, making the terrain modification results closer to reality, thus provides a new method and technology for the detailed representation of earthquake scene.⑤Reseached the dynamic plotting system construction for earthquake disaster information expressionThe effective expression and visualization of earthquake disaster information is a necessary function of the earthquake emergency commanding system. To represent each kind of disaster information by visualization, this paper focuses on the three-dimensional dynamic plotting technology, puts forward the real-time dynamic plot hierarchical framework of earthquake disaster information. The whole system is divided into geometry layer, unit layer and semantic representation layer, the key problems such as the construction of plotting symbols and the match of plotting symbol and the terrain are discussed and solved. The application of plotting technology is extended faced to the spatial and temporal semantics of earthquake disaster information, and effectively represents each kind of earthquake disaster information through the combination of GIS spatial analysis,3D measurement, muti-dimontional linkage, dynamic simulation, etc.