Abstract
In 3D CAD systems, it is not always possible to convert trimmed surfaces to the intended shapes upon data exchange between different CAD systems because the definition of trimmed surfaces is not unified among the CAD systems. If a shape can not import to a CAD system, the shape should be modified to suit to the system. But many problems to improve the shape arise. To solve the problems, it is effective to generate a new surface from the boundary curves and delete the invalid one. If insufficient information on the features of the original trimmed surface is applied, the intended surface cannot be estimated from the boundary curves. Even if surface can be estimated, the quality of the surface is low. We, therefore, focus on the tangent vectors of the original source surface in the U and V directions on the boundary curves of the trimed surface. In this paper, we present a new method to generate the new source surface by using the boundary curves and the features of the original source surface. In our method, at first, the first derivative vectors are calculated at the start and end points of each boundary curve and the division points on the curve segment of the source surface in the U and V directions. Next, the projection plane is defined whose origin is the maximum and minimum points of a boundary curve in the UV space and normal vector at the origin is the tangent vector of the original source surface. The offset direction is calculated by linear interpolation of the first derivative vectors in the U and V directions for each boundary curve, and the boundary curves are offset to the projection plane. Finally, a region enclosed by the offset four free-form curves is interpolated by a B-spline surface to create the new source surface.
