NURBS BOUNDARY GREGORY PATCH AND ITS SHAPE CONTROL

Since the body shapes of industrial products contain various kinds of free-form surfaces, designers need a 3D CAD system with which they can easily design such surfaces. This paper proposes a new method of modeling the free-form surface with a NURBS boundary Gregory patch. This patch, bounded by four NURBS curves, can be easily connected to other surfaces with G¹ continuity. In this paper, two methods that modify the surface shapes are described. One method modifies the direction and length of a tangent vector on the surface boundary, and the other controls the center area shape of the surface by moving a point on the surface. We have developed these capabilities on the solid modeling toolkit called DESIGNBASE. This system enables designers to dynamically control the surface shape, as they observe the parametric lines and curvature radii.