【作者】 徐飞；

【导师】 张爱军；

【作者基本信息】 北京化工大学 ， 机械电子工程， 2009， 硕士

【摘要】 树木和地形的可视化研究是当前视景仿真领域研究的热点。如何在绘制质量和绘制速度这对矛盾中找到一个平衡点,是该领域研究的重要内容和目标。在树木可视化方面,本文首先研究了已有的主要算法,包括分形理论中的L-系统法、迭代函数系统法和粒子系统模型法;以及基于图像的树木绘制方法,包括Billboard模型及其变体和层次纹理映射模型。比较了这些方法的优缺点和适用场合。在综合比较已有树木算法的基础上,提出了在HSV色彩空间中基于图像的层次感树木可视化方法。该方法针对二维树木图像,利用HSV色彩空间对其进行分层提取处理,提取出若干层带有伪深度信息的图像,然后再将这些图像进行叠置、融合,构建出具有一定层次感立体效果的树木可视化模型。经实验验证,该方法建立的模型预处理过程简单省时,显示效果良好,具有一定的应用价值。在地形可视化方面,本文介绍了基于Heightmap的地形绘制的基本方法,以及生成Heightmap的两种算法,即断层生成法和中点位移法。在此基础上,开展了基于LOD的地形可视化技术的应用与实现。重点研究了基于Geomipmapping和基于四叉树的LOD算法的原理与实现。探讨并解决了实现过程中存在的裂缝、节点评价和视景体裁剪等问题。实验结果表明,地形绘制的真实度高,能够展现出一定的LOD效果,同时满足实时性要求,具有广泛的应用价值。更多还原

【Abstract】 Visualization of trees and terrain has become a research focus in present scene simulation, in which how to balance the quality and speed of rendering is one of the important topics of the research.In aspect of trees visualization, some current typical algorithms of tree visualization are firstly studied, including L-system, Iteration function system and Particle system in Fractal theory as well as Billboard and its variants and Layered texture mapping model based on Image-based rendering (IBR). Meanwhile, advantages and disadvantages as well as applicable situations of these algorithms are compared.On the basis of analysis and comparison of the existing algorithms, a new visualization method of trees using HSV color space based on IBR is presented. This method focuses on 2D tree image. Firstly, several sets of different color information, which is called as pseudo-depth information, are extracted in HSV color space from one image of tree. A few images, each of which is composed of the set of extracted color information, therefore are obtained. Finally, the images are arranged in specific distance in Euclidean Space to create the depth feeling in displaying. The experiment demonstrates that the visualization method of tree is simple and time-saving, and the effect is good and applicable.In aspect of terrain visualization, the fundamental methods of terrain rendering based on Heightmap are introduced, and two methods of Heightmap generation, such as Fault formation and Midpoint displacement, are described as well. The principle and realization of LOD algorithms based on Geomipmapping and Quadtree are especially discussed, and the application and implementation of these methods are developed accordingly. Some existing problems in the process of implementation, such as cracks precaution, nodes evaluation, view frustum culling and so on, are investigated and solved. The running results offer a strong sense of reality and certain effect of LOD, and demonstrate that the terrain visualization methods mentioned above are capable of meeting the real-time requirements and are applicable for scene simulation.更多还原