采用推理方法提高多面体Boolean运算的可靠性

提高实体Boolean运算的可靠性是几何造型中最基本也是最迫切的工作。通过对国内外几何造型系统在实体Boolean运算可靠性方面的测试,我们发现,实体Boolean运算不可靠是一个普遍现象,运算失败的根本原因在于数值计算存在误差。数值计算误差决定了我们不能精确地确定集合成员分类。集合成员分类的结果与选定的计算容差有关,具 有相对性。从而相关分类之间会发生冲突。一旦分类之间发生冲突,Boolean运算就不能得到正确的结果。我们提出了一个相当可靠的Boolean运算算法。该算法采用推理的方法在进行Boolean运算之前解决由数值计算误差所引起的相关分类之间冲突。这些算法已在Apollo和SUN工作站上实现,并取代了GEMS 2.0造型系统,构成了一个新的造型系统GEMS 2.1。经测试和比较,这个系统的可靠性比SDRC公司的Geomod 3.9和Intergraph公司的I/EMS高得多。

AN REASONING APPROACH TO IMPROVE THE RELIABILITY OF BOOLEAN OPERATION ON A. PAIR OF POLYHEDRA

It is essential and pressing to improve rebobility of Boolean operations in geometric modelling systems. The Boolean operations in commercial systems now available are not reliable enough because of numerical calculation errors. Numerical calculation errors make us unable to determine set membership classifications exactly. Some classifications are ambiguous because they are dependent on adopted computing tolerance. Thereby interrelated classifications may conflict with each other and it is very difficult to get correct results of Boolean operations in many cases.We introduce a reliable Boolean opration algorithm which solves the conflicts among interrelated classifcations before implementation of Boolean operation by use of reasoning technique.The algorithm has replaced the modelling module of the geometric modelling system GEMS 2.0 to forma new system CEMS 2.1 on Apollo and Sun workstations.According totests and compared with Geomod 3.9 and I/EMS,CEMS 2.1 is much more reliable.