基于图形旋转系统的渐进层次细节和拓扑改变操作

针对现有的层次细节方法不能一直保持模型的二维流形性,提出2种基于图形旋转系统的拓扑改变操作Cut Tunnel和Create Tunnel。Cut Tunnel操作算法通过输入环绕待切断柄的1条封闭轨迹的顶点集合,然后删除所有与这些顶点相连的边,从而切断1个复杂的柄。Create Tunnel是Cut Tunnel的逆操作。在此基础上,提出1种渐进层次细节理论框架,框架采用基于图形旋转系统的数据结构表示模型网格,分为生成层次细节过程和使用层次细节过程2个过程。生成层次细节过程能够改变模型的拓扑,并自动生成连续变化的细节层次网格;使用层次细节过程使模型从某一层次细节的网格逐渐变形到任意层次细节的网格,并始终保持模型的二维流形性。对Stanford大学的buddhaf模型进行拓扑改变操作、生成渐进层次细节和运行层次细节的试验。结果表明:拓扑改变操作及渐进层次细节理论框架效果良好,模型始终保持了二维流形性。

Progressive LOD and Topology Operation Based on Graph Rotation System

Current LOD(Level of detail) method can not preserve 2-manifold of models.In this paper two topology operations,CutTunnel and CreateTunnel,are presented.By inputting a vertex set which belongs to an edge track around the tunnel to be cut into CutTunnel operation algorithm,the algorithm deletes all the edges connected to the vertex in vertex set.Thus the tunnel is cut.CreateTunnel operation is the reverse operation of CutTunnel.Based on these,a new progressive framework is presented.In this framework the data structure based on graph rotation system is used to represent meshes.The framework can be divided into two procedures: create LOD procedure and use LOD procedure.Create LOD procedure can change the topology of models,and automatically produce progressive LOD meshes.Use LOD procedure can gradually change the model from one level to another level of LOD.This framework can preserve 2-manifold of models.We test the topology operations,create LOD procedure and use LOD procedure by using the buddhaf model of Stanford University.The result shows that our framework and topology operations work well and the results are satisfying.The model has been preserving 2-manifold during the whole test.