虚拟城市场景建模方法与技术研究

虚拟城市场景建模是虚拟城市设计的重要内容，它包括地形地物建模，纹理映射以及视觉效果处理等内容。地形建模需要进行模型分解，求解法向量和定义颜色；地物建模需要进行二维三角网剖分，不透明和透明单面构造。纹理映射技术将像片纹理和地形地物融合，用来增强地形地物的显示效果。视觉效果处理主要采用消隐处理，光照显示，浓淡处理与透视显示等技术。层次细节纹理技术可以改进虚拟城市复杂场景绘制速度，但在可视化表现时必须使表现信息量和可视速度之间有一个折中，最好的办法是采用多级LOD，在不同的可视化阶段采用不同的LOD。

Technique and Method of the Scene's Modeling of Virtual City

The scene modeling is an important step to design Virtual City, which includes 3D models of terrain and surface features building, textures mapping and special effect designing. In order to construct terrain model, it is necessary to divide the surface into small parts, calculate the normal line and define color for each part; In order to make surface features?model, it is required to divide the surface into 2D triangular pieces, construct transparent and opaque face. The texture mapping is used to improve the scene of Virtual City by joining the photos with terrain and surface features; special effect designing is used to make the special sight effect for Virtual City by the techniques such as elimination, illumination and perspective. The technique of LOD (level of detail) can be used to improve the running speed of the complicated scene model of Virtual City, but certain compromise between detail information and speed need to be made by adopting the technique of multilevel LOD and by using different LOD at different time while drawing the scene.