三维树木模型在虚拟地理环境, 三维城市场景等领域中应用广泛, 但由于树木中包含丰富的几何信息, 难以对大规模的森林场景进行有效的渲染. 为此我们设计了一种基于视点互信息(Viewpoint Mutual Information, VMI)的树木实时简化方法. 在预处理中按照树枝间的拓扑关系将树木划分为具有父子关系的节点, 然后根据VMI计算每片树叶在多个视点下的平均重要度并以此对树叶进行排序, 重要程度较小的树叶在简化过程中将会被优先删除. 实时简化过程中, 我们提出了一种视点依赖的简化方法, 大大降低了需要渲染的数据量. 为了提高渲染森林场景时的性能, 我们使用了多种渲染优化措施以避免不必要的细节层次(Level Of Detail, LOD)切换.
The three-dimensional tree model is widely used in the fields of virtual geographic environment, three-dimensional city scenes, etc. However, due to the rich geometric details of trees, it is still a huge challenge to effectively render trees in large-scale forest scenes. In this study, a real-time simplification method for tree foliage based on Viewpoint Mutual Information (VMI) is proposed. In the preprocess, the whole tree is divided into parent-child branch and leaf nodes according to its own topological relationship. Then, the average importance of each leaf under multiple viewpoints is calculated based on the VMI value and the leaves are sorted based on it. The leaves of less importance are pruned first during the real-time simplification process. In the real-time simplification process, we propose a view-dependent simplification method which greatly reduces the number of primitives needed to be rendered. In order to improve the rendering performance in forest scenes, a variety of rendering optimization measures are taken to avoid unnecessary Level Of Detail (LOD) transition.