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Three-Dimensional Simulation System for Virtual Environment in the Yellow River Basin

LIU Gui-fang 1,2,LU He-li 2,3,SUN Jiu-lin 2,3,QIN Yao-chen2,XU Shu-ming2(1.Institute of Natural Resources and Environmental Science,Henan University,Kaifeng 475004,China;2.College of Environment and Planning,Henan University,Kaifeng 475004,China;3.Institute of Geographical Sciences and Natural Resources Research,CAS,Beijing 100101,China)  
Virtual Reality technology is a type of human-machine interface for simulating human behaviors such as vision,hearing and movement.With a 3D helmet,data glove,3D mouse,data clothing and stereo earphone,people can be immersed in a special 3D digital graphic environment,and can operate within this environment to realize a given purpose.Traditional visualization methods include paper and digital maps which emphasize spatial data displays.In contrast,Virtual Reality,with the capabilities of multiple sensory immersion,interaction and autonomy,allows for 3D dynamic real-time map displays.By using Virtual Reality,not only can models be built in multi-dimensional data space but also high-level abstract knowledge can be acquired and new concepts can be formed by the user.The Virtual Yellow River System includes five major modules:data sources,3D simulation terrain database,3D simulation model database,3D simulation implementation and an application system.Data sources included DEM data,terrain element vector data,geographical texture data,3D model data and geographical element texture data.The 3D simulation terrain database was used for terrain scene display.The 3D simulation model database was used for 3D model display.The 3D simulation implementation was used for various kinds of mutual operation(such as Keyboard Navigation and Route Navigation) in the 3D scene.The application system enabled the realization of the 3D target management and the mutual response between the 3D scene and 2D electronic map.The data sources for the Virtual Yellow River System included 30m resolution ETM+ image of the Yellow River(September 2001),1:50000 DEM data of Henan Province,texture maps of Yellow River,the urban architecture layout of Henan,and building models and digitized maps.The data processing software included ESRI ArcGIS 8.3,ArcView 3.2,ERDAS IMAGINE 8.6,MapInfo 7.0,Terra Vista 4.0,Multigen Creator 2.5.1 and Adobe Photoshop 7.0.In the 3D navigation system,the viewpoint was the "avatar" of the eyes and its function was similar to a camera in the real world.Navigation in 3D space was a kind of 3D drawing process,constantly moving the viewpoint and changing the sight direction which could be oriented through the viewpoint position.So by constantly changing viewpoint and position,3D scene navigation is actualized.Keyboard Navigation and Route Navigation are two typical kinds of 3D scene navigation.OpenGL technology was implemented to realize the real-time dynamic display.MO and OpenGL technologies were used to create the mutual response between the 3D scene and 2D electronic map.As a result the advantages of both the 3D scene and 2D electronic map were brought into full play.The macroscopic view,integration and conciseness of the 2D electronic map and the locality,reality and visualization of 3D scene were combined.Also,the disadvantages of abstraction and ambiguities of the 2D electronic map and the loss of direction in virtual navigation of the 3D scene were overcome.
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