IGES边界模型转换中的参数域重构与修正算法

A Parameter Domain Reconstruction and Revision Algorithm for IGES B-rep Model Transformation

针对IGES边界表示模型中可能缺少参数域信息的情况,在总结常见曲面上曲线参数域反求方法的基础上,通过分析可能出现特殊母线边计算错误和缺少退化边的问题,提出一套从三维空间曲线到二维参数域曲线的修正算法.该算法中,对只有一条边的环,仅需处理缺少退化边的错误;对多于一条边的环,通过判断相邻环边中参数域端点处离散线的几何位置关系,分2步分别修正特殊母线边的计算错误和添加退化边;同时以NURBS曲面为例,重点讨论了基于三维空间信息的参数域歧义情况判定及处理算法.在TiGems7.0系统中的实验结果表明,该算法不依赖于求交运算中造成的数值误差,具有较好的鲁棒性,能够实现IGES的边界表示格式在Solid Works,Pro/E等系统中的数据交换功能.

For the case that B-rep models of IGES may be lack of parameter domain, this paper analyzes the problems of degenerative edges and special generatrix edges when recalculating the parameter domain of curves on surfaces directly, and presents an algorithm for amending the parameter domain information. If a loop contains a single edge, only degenerative edges need to be appended properly; otherwise, we take two steps to revise the special generatrix edges and append degenerative edges respectively, according to the geometric relationships between discrete lines on parameter domain of adjacent edges. We also take the NURBS surface as an example, and propose an algorithm which can determine and process the ambiguity of parameter domain based on 3-D spatial information of surfaces. Experimental results in TiGems7. 0 illustrate that this algorithm is independent of the numerical error accumulated in intersection computation, and can implement the data exchange of IGES B-rep model built by different CAD systems such as SolidWorks and Pro/E.