【作者】 孙艳英；

【导师】 杨克俭；

【作者基本信息】 武汉理工大学 ， 计算机软件与理论， 2004， 硕士

【摘要】 近些年来，随着真实感计算机图形显示技术的发展和硬件的快速发展，为人们描述现实中的三维世界提供了很大的方便和可能性。而且各个领域对计算机图形技术的要求已经不再局限于生成平面的静止的图形。随着计算机仿真、虚拟现实、三维游戏的发展，三维场景的创建及其实时渲染显得越来越重要了。 本文结合国家自然科学基金的项目《分布交互三维行为—特征建模方法的研究》和《分布交互三维仿真平台的开发》，主要研究了三维场景建模及其实时渲染方法，内容涉及到以下几个方面：数字地形模型的生成、三维地形的改造、三维地形的实时渲染方法、真实感地形的生成技术。 本文第1章主要介绍课题的来源，本课题研究的目的和意义，以及本文用到的一些关键技术。 第2章给出了两种生成地形模型的方法。一种是基于位图的生成方法，该方法是依据位图的灰度等级与地形的高程之间的映射关系，来创建地形的模型；也就是位图的最低灰度对应地形的最低点，位图的最高灰度对应地形的最高点。另一种方法是基于等高线的方法，该方法是通过对等高线进行编辑，保存相应点的高程，再根据线性插值，得到各个网格点的高程，从而生成对应的地形模型。 第3章介绍了地物模型的创建方法。根据地物模型与地形三角网的关系，地物模型分为两类：一类是与地形相关的地物，如河流、湖泊、山体等；另一类是与地形无关的地物模型，如树木、建筑物等。对于第一类地物模型的创建，本文提出并实现了自然堆积算法；对于第二类地物模型的生成，本文采用的是Billboard算法，它是用二维的图像来代替三维的模型。 第4章介绍了地形的实时渲染方法。当我们要生成相当真实感的场景时，由于地形的复杂性，要实现实时性，往往是不太可能的。我们必须从场景的本身的集合特征入手，通过适当的方法来简化场景的复杂性。层次细节(Leve1s of Details)技术就是在这样的情况下提出来的。本文介绍了基于四叉树LOD、基于二元三角树结构的法则ROAM，而且提出并实现了基于过渡带的LOD。 武汉理工大学硕士学位论文 第5章介绍了真实感场景的生成技术。要渲染出真实感的场景，必须要考虑到下列情景，地形表面要有更多的细节、要渲染地表植被等，甚至各种天气效果。所有这些都能让场景看起来更加的自然，更加的逼真。本章主要介绍了天空的生成技术，光照、材质、雾化特效，纹理贴图，地表的细节等技术。 第6章是总结全文，展望下一步的工作。更多还原

【Abstract】 Recently, With the development of the photo-realistic display technology of computer graphics and the computer hardware, it’s probable and convenient for us to describe the three dimensional world. What is more, the requirement of all kinds of fields to computer graphics technology is not confined to the plain and still graphics. With the development of computer simulation, virtual reality, three-dimensioned game, it’s more important for the 3D scenery to build and real-timely render.The paper, which is based on the project of National Science Fund -Behavior-Characteristic modeling for Distributed & Interactive 3D Scenery and the project the Development of Distributed and Interactive 3D Simulation Platform, chiefly research the modeling of 3D scenery and the method to real-timely rending the scenery. The paper mainly involved four parts: the generation of digital terrain model, the rebuilding of 3D terrain, the method to real-time rendering 3D terrain, the technology of the photo-realistic terrain generation.In the first chapter, there mainly introduce the source, the research purpose and the significance of the project. The key technologies involved in the paper are introduced, too.In the second chapter, there provide two methods to generate terrain model. One is based on bitmap. This way is in light of the mapping between gray levels of the bitmap and the height of the terrain. In other words, the minimum gray point is the lowest terrain and the maximum gray point is the summit. The other is based on contour line. The way is that first editing the contour line, then saving these heights, finally depending on linear calculating middle value, thus getting the height of every mesh point, and the 3D terrain model.In the third chapter, there principally introduce the method of ground objects model generation. On the grounds of the relation of the ground objects model and the terrain model, we can assort them into two kinds. One is inIIIrelation to the terrain, such as river, lake, artificial hill etc. The other is not in relation to the terrain, for example tree, simple building etc. As for the first ground objects model, I expound and realize natural piling algorithm; as for the second, the paper adopt the billboard algorithm that use 2D image in place of 3D models.In the forth chapter, there introduce the real-time rendering method of terrain. When we generate quit photo-realistic scenery, but because of the complication of terrain, it’s impossible to realize the real-time rendering. We must simplify the complication of terrain resting on its characteristic. The LOD technology was proposed in this environment. In the paper I propose and realize the LOD based on transitional band. Quad tree algorithm and ROAM algorithm are depicted in detail.In fifth chapter, there introduce the generation technology of photo-realistic scenery. If we want to render out photo-realistic scenery, we should consider these circumstance: the terrain surface with more detail, rendering ground vegetation, even all sorts of weather effects. All of these can make scene more natural, more real. This chapter chiefly introduces the technology of sky generation, lighting, material, fog, texture, the detail of terrain surface.The sixth chapter summarizes the paper, and prospects the next work.更多还原