【作者】 王丽芳；

【导师】 韩燮；

【作者基本信息】 中北大学 ， 计算机应用技术， 2007， 硕士

【摘要】 虚拟现实技术在计算机仿真、数字地球和游戏娱乐等领域都有广泛的应用。这些应用不仅要生成高度真实的复杂虚拟环境,而且用户要和虚拟环境进行互动,增强交互性和沉浸感。使人可以随心所欲的在环境中漫游,跟在真实的环境中体验一样。随着虚拟现实技术应用的深入,人们对虚拟场景的要求越来越高,远远超过了计算机图形硬件实时处理能力。因此如何在PC机上进行三维地形场景的真实感绘制是一个挑战性课题。本论文从分形理论,三维地形建模和虚拟场景三个方面逐步进行了深入讨论。首先,讨论了基于OpenGL三维图形库及其工作原理,对三维真实感地形生成的基本过程进行了详细剖析,提出了一些加强渲染效果的具体措施。其次,基于分形的原理,对采用分形布朗运动模拟地形的方法进行了系统研究,给出了采用随机中点位移法中的“diamond-square”算法实现分形地形模拟的具体细节。第三,为了使生成的三维地形更具实时性,提出了一种改进的实时连续LOD生成算法。该算法首先采用Mortan码的编码方式对地形数据进行简化,并利用不完全四叉树存储简化后的高程数据;然后根据视点位置和网格空间对象误差的关系建立基于不完全四叉树的LOD模型,同时采用逐层找邻法调整不同层次之间的裂缝,并给出了寻找不同类型邻居的实现过程;最后采用背面剔除算法将起伏地形的不可见部分去除。实际编程时,由于采用了Hibert填充曲线方式存储四叉树结点,并采用隔层四叉树方式访问结点数据,从而提高了大规模地形的绘制效率,取得了良好的地形实时绘制效果。更多还原

【Abstract】 Virtual Reality has been widely used in the fields such as computer simulation, digital earth, game and entertainment, etc. These applications need not only realism complex Virtual Environment, but also require the user to interact with the virtual scenes at interaction frame rate. As long as meeting the real-time rendering, the user can feel the virtual environment which is the same as the real world and immerse into the environment. However, Virtual reality communities and other visualizations have always faced the problem that their "desirable" visualization dataset sizes are one or more orders of magnitude larger than what the hardware can display at interactive rates. Thus Realistic rendering of 3D terrain scenes is a challenging subject.Fractal theory, 3D terrain modeling and virtual scene are discussed in details. Firstly, based on OpenGL library and its work principle, the process of 3D real-time terrain surface rendering is analyzed at length. Some methods are presented to improve rendering effects and to speed up graphic display. Secondly, on the basis of fractal theory, the terrain simulation is systematically studied and carried out by using fractal Brown motion (FBM) method. For the fractal terrain simulation, the "diamond-square" algorithm based on random midpoint displacement (RMD) is given in detail. Thirdly, in order to render 3D terrain in real time, this paper presents an improved LOD algorithm. This algorithm firstly simplifies the DEM data by using Mortan coding principle and stores the simplified data with an unfull quatree. Then, it builds the real-time continuous LOD based on this unfull quadtree according to the relationship between viewer position and grid object space error. The author brings out a method named“find the neighbors layer by layer”to patch the cracks between different layers and the procedures to find the different type neighbors are presented in this paper. Finally, it wipes off the invisible grids through back-culling algorithm. In order to improve the rendering speed during the programming, it uses Hibert filling curve method to store and interleaved quatree method to access the unfull quatree nodes. The author uses the improved method to simulate the terrain area and obtains a good effect.更多还原