细分造型技术在CAD系统中的应用研究

Research on the application of subdivision modeling in CAD systems

在现有CAD系统中通用的NURBS造型对于非规则拓扑关系的曲面的表示存在着拼接、剪裁困难、表达难以准确等缺点 ,而在实际工程应用中形体轮廓复杂、难以通过基本体素复合且要求光滑的实体又普遍存在。细分造型计算简单 ,可以表达任意拓扑关系 ,在图形学中已得到广泛研究。本文阐述了细分造型的原理和方法 ,提出了在现有CAD系统中应用细分造型的方案 ,对细分造型中的网格生成、边界限定、法线控制、NURBS补片转换等关键技术进行了研究 ,初步构造了细分造型的原型系统 ,可极大地缩短复杂曲面形体的造型时间 ,取得了良好的实践效果。

In existing CAD systems, classical NURBS patch method is used to build solids of irregular topology with some drawbacks: difficult patching_up and trimming, expensive computing and hard exact representing. However, in practical engineering application, there are many solids with complex shape, which require smooth ness and are difficult to be combined with basic elements. Subdivision modeling is a new and easily computing method, and can represent arbitrary topology, which has been widely researched in CAD. In this paper, the principles and methods of surface subdivision are described, and the kernel technologies for subdivision including mesh creation, boundary control, normal control, transformation from subdivision mesh to NURBS patch , Boolean calculation, etc., are studied. A scheme of using subdivision modeling in existing CAD system is presented, and a prototyping system of subdivision modeling is constructed. The experiment proves that by using this scheme, the modeling time is shortened and the efficiency is improved.