| With the rapid development of“Digital Ocean”, there are higher demands for the virtual of true feeling environments and the reveal of the rules hidden in massive marine data. In VV-Ocean (Ocean Oriented Virtual Reality and Visualization System), all kinds of land-sea terrains can be rendered, besides, a waterbody rendering engine is established to render all kinds of waterbody elements in 3D space. At the same time, a variety of ocean monitoring and remote sensing data is expressed intuitively in the virtual environment. For regional, hemispherical, and global areas, roaming anywhere at any angle of view and geospatial analysis are interactively obtained and dynamically presented. Main works are:(1) Research on data organization and rendering methods of all kinds of land-sea terrainsThe foundation of this research is the rendering of multi-scale land-sea terrain. The traditional quadtree method and the latest Geometry Clipmap method are separately used to express surface topography; by contrast, the latter one is selected for the rendering of urban area. Transformation and data organization strategies are separately proposed for both hemispheric area and global area which are rendered through Geometry Clipmap way. On the one hand, satisfying efficiencies and effectivenesses could be achieved; on the other hand, coordinates query and profile analysis can be implemented on all kinds of virtual terrains.(2) Research on the real-time rendering of highly realistic marine environmentThe core of this research is the real-time rendering of realistic marine environment. Dynamic water surface are simulated in real time based on GPU vertex textures created by continuous height maps; dynamic lighting, real-time reflections and caustics are created through normal textures, reflected textures and caustic textures which are sampled in GPU pixel shaders. Three-dimensional modeling, transparent mapping and particle system are used to produce rays, fog and bubbles in the submarine space; at the same time, path planning and obstacle avoidance methods are designed to drive the virtual fish. All of the elements above comprise rich and realistic virtual marine scenes.(3) Research on dynamic visualization of multi-dimensional marine data in the virtual environmentReal data is the basis of analyzing, investigating, and predicting ocean properties and phenomena. The characteristic feature of this research is seamless integration of virtual reality technology and visualization technology. In VV-Ocean system, visualization works of sea surface data are combined with sea water rendering, waterbody data are displayed in the form of point rendering, line rendering, surface rendering and volume rendering. Furthermore, dynamic broadcasting of continuous data in the time dimension could be executed as needed, and a separate window is provided as needed for the output of visualization results. The system has integrated the interactive characteristic of virtual reality technology and intuitive characteristic of visualization technology, and it may assist the ocean related researchers and experts in depicting, understanding, and forecasting marine data and phenomena in the virtual environment.(4) Research on system integration technologies of land-sea oriented virtual reality platformOn the basis of urban simulation oriented VRGIS platform, a land-sea oriented platform is developed relying on the integrating of VV-Ocean technologies. Waterbody rendering is encapsulated as a plug-in and water areas can be edited easily in the integrated platform. At last, land-sea oriented geospatial analysis, interactive query, and random wandering can be carried out in the virtual land-sea environment.Several effective practice are done during the process of my work, including rapid rendering of multi-scale terrains, comprehensive displaying of dynamic submarine scenes in a 3D rendering engine of waterbody, and intuitive expression of multi-dimensional marine data. Main innovative aspects are:(1) Uniform sampling methods and mosaic display algorithm of multi-scale land-sea terrainsThe uniform sampling work flow and rendering flow are separated, and different rendering methods are provided for areas of different scale. For the rendering of hemispheric scale and world scale terrains, data organization and transformation methods are separately provided. At last, not only spherical tarrain of global scale, but also flat terrains of both urban and polar scale could be rendered in real time by means of Geometry Clipmap. For all kinds of terrains, it is easy to do coordinate querying, camera positioning, and interactive roaming with the help of forward and backward coordinate mappings. In addition, an algorithm of mosaic display of local terrain in the global spherical terrain is proposed.(2) Construction of texture based 3D rendering engine for dynamic marine waterbodyConsidering physical characteristic of wave, light, and collision, a marine waterbody 3D engine is established to deal with the rendering of lighting effects, real time reflections, rays, bubbles, fish, etc. To make full use of the GPU texture cache and explore the accelerateon ability of GPU rendering, dynamic vertex textures, normal textures, caustic textures and reflection texture are widely used for all kinds of ocean effects. The waterbody 3D engine solves a series of ocean related virtual reality problems, such as dynamic lighting effects, real time reflections, path planning of the virtual fish, complex collisions in the submarine space, mixture of caustics effects and so on.(3) Seamless fusion of 4D visualization works and realistic water rendering through GPU programmingThe model and work flow of simulated water is improved for the visualization of sea surface data. Sea surface data (especially MSLA data) is visualized in the longitude dimension, the latitude dimension, the altitude dimension, and the time dimension using the same mesh that is used for the rendering of simulated water. To switch between visualization work and simulation work with flexibility, the positions of the vertices are manipulated by one GPU vertex program, and the colors output are manipulated by one GPU fragment program. One the one hand, the dynamic water surface could be displayed; on the other hand, the distribution and rule of marine data could be expressed intuitively. This is specific and effective practice in combining the real data based visualization work with 3D simulation work. |
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