抄録
In three dimensional solid modeling, there are mainly two types of modeling, CSG (Constructive Solid Geometry) and B-Reps (Boundary Representations). CSG is a human oriented model because it is constructed by combination of primitives. B-Reps is an application oriented model but if designer try to construct 3D shapes by B-Reps directly, many difficulties arise. So it is the best way that the designer makes shapes by CSG, and B-Reps is automatically generated from CSG for computer processing. This paper proposes a method of automatic generation of B-Reps model from CSG model in an analytical way. It is not aprroximate ones but the exact quadratic surfaces are treated. And intersectional curves are derived by an exact analytical method among these surfaces. For getting shape edges from intersect curves, it is shown how to use the CSG structure and how to treat the co-lying surface problems. After creating all geometrical information of B-Reps, topological information of B-Reps is constructed by determining the coordinates of both terminal points of edges and by checking the information of two surfaces to which each edge belongs. To demonstrate this method, the CSG-B-Reps conversion system EAGLE is made, and many experiments are executed.
