Research And Realization Of An Integrated VRGIS Navigation Platform For City/Region Simulation

VR-GIS is a new technique that integrates GIS with VR. It's a result of development of GIS technology from two-dimensional to three- and even multi-dimensional, and from static to dynamic. As one of key technologies that are used to establish "Digital Earth", "Digital City". This dissertation takes kinds of key technologies of VR-GIS as the main research object and the main aim is to construct an integrated platform of VR navigation and GIS analysis for city/region simulation. To solve the problems of massive data organization, management, real-time visualization and seamless integration of VR and GIS, this paper carries on the research about software integration methods based on plug-in technology, and spatial data engine of 3D city models based on IOCP technology, GPU-based hardware acceleration technologies, the method of integration of VR and GIS. Based on the research achievement, VRGIS platform has been researched, which can satisfy the high requirements of landscape simulation and management for large cities and regions. The main contents and innovations in this dissertation are summarized such as:(1) Plug-in software architecture of VRGIS platformUsing plug-in technology to integrate the data processing method, such as data management, three-dimensional rendering and 3DGIS analysis, can improve the capacity and degree of methods reuse. Because of such domain characteristic that VRGIS platform has many application fields, fully considering technology advantages of the high component encapsulation and reuse, multi-layers plug-in architecture software development model has been established, which can provide VR-GIS developers a plug-and-play component library.(2) Digital city 3D models data engine based on IOCP3D models are important geographic objects in VRGIS system and are the three-dimensional spatial basis of virtual environment. To solve the difficulties of data loading delay when viewpoint updates, data management should satisfy the needs of VR navigation and GIS analysis, this dissertation uses the spatial data management idea of GIS software, several levels of city models are explored and their respective features are analyzed. Fully considering such characteristics that LOD, texture mapping, precision asymmetry, the data organization methods of Precision LOD R-tree and Hilbert grid respectively for building layer and hybrid layer are designed. Based on this spatial data index, an out-of-core VRGIS data engine is developed using the technologies of multi-thread and IOCP. As a result, there-dimensional models are loaded with low delay by building a memory buffer with LRU algorithm.(3) GPU-based virtual city rendering acceleration technologiesHigher rendering performance requirements of virtual scene are proposed for kinds of digital city applications. In order to satisfy these requirements, on the basis of traditional optimize technologies such as LOD, VBO, display list, frustum culling, this dissertation discusses an optimal hierarchy occlusion culling algorithm based on GPU, designs a billboard rendering algorithm and an indicative building rendering algorithm based on GPU, implements particle system rendering based on GPU. It is useful for the optimization of three-dimensional display engine and the increase of visualization efficiency by using these algorithms.(4) Seamless integration of VR and GISData sharing and function unification are the main goals of the integration of VR and GIS. By abstracting VR data and GIS data uniformly and inheriting their traits, the platform provides uniform external access interface and keeps nodes have their own render and access mode. In this way, unification and sharing of VR and GIS data are achieved. This dissertation discusses in-depth the integration points of VR and GIS, realizes 3DGIS functions including three-dimensional measurement and path analysis based on the rendering of DEM terrain, takes sunlight as an example, imports the model of virtual sunlight, explores shadow generation method, sunlight analysis and sunlight data generation method based on VR scene, which has creative sense for VRGIS application.This dissertation takes the key technologies of virtual city as research objects and the main innovations are summarized as follows.1) Massive virtual city 3D models data engine has been constructed. By analyzing features of city models, the novel data management methods of Precision LOD R-tree and Hilbert grid respectively for building layer and hybrid layer are designed. With IOCP technology, the 3D models data engine has been developed, which enable VRGIS platform can process massive spatial data.2) Billboard cluster rendering algorithm and building image fusion algorithm based on GPU. This dissertation realizes massive billboard objects rendering by making use of GPU programming technology. Furthermore, the algorithm of building image fusion combines rendering optimization and virtual navigation, which is an effective try of GPU image fusion used to virtual city simulation.3) Realization and seamless integration of 3DGIS in virtual city. This dissertation takes the virtual scene as data source of 3DGIS analysis, realizes the functions of real distance measurement, surface area measurement, volume measurement and path analysis based on 3D vector data. Furthermore, the physical model is built in the virtual scene, which promotes the integration of VR and GIS.