基于局部协调设计的复杂自由曲面模型拓扑还原技术

Topology Recovery Technique for Complex Freeform Surface Model Based on Local Consistent Mending

针对局部协调设计因引入协调曲面而破坏了模型原有的拓扑结构并同时增加了自由曲面形状造型所需的曲面片数量,提出一种基于局部协调设计的复杂裁剪汇交曲面模型拓扑还原技术。逆向定位汇交点(N面角点)并完整构造出决定还原后N边汇交曲面模型拓扑、几何形状和边界的特征曲线网格。应用自由曲面逼近技术分片逼近经裁剪汇交曲面和协调曲面离散获得的点云数据重建B样条曲面以实现裁剪汇交曲面的拓扑还原。采用自由曲面模型的全局美化技术实现紧公差约束下对点云逼近的N张拓扑还原后汇交曲面的全局美化,保证曲面相邻边界和N面角点处收敛的G1光滑拼接。应用实例表明,该拓扑还原技术不仅较好复现了原始汇交曲面模型的拓扑与几何性质,并且使模型达到整体G1连续。

Considering that the local consistent mending technique destroys the original model topology and increases the number of surface patches needed for freeform surface shape modeling, a topology recovery approach dealing with complex trimmed confluent surface model based on local consistent fitting is proposed. The N-patch comer of topology recovery model is relocated and the complete curvilinear grid is constructed, which determines the topology, geometrical shape and boundary of recovery N-sided confluent surface model. The freeform surface approximation technique is utilized to approach point cloud sampled from trimmed confluent surface and consistent surface to reconstruct B-spline surface in order to recover the topology of trimmed confluent surface. The multiple recovery surfaces approximated to point cloud subject to tight tolerance are beautified globally, which generates convergent G1 continuity between adjacent B-spline surfaces and smoothly stitches the N-patch comer. Practical application shows that the presented topology recovery technique not only recovers the topological and geometrical properties of original confluent surface model, but also achieves global G1 continuity.