COMPARISON OF SURFACE AND DERIVATIVE EVALUATION METHODS FOR THE RENDERING OF NURB SURFACES

Three methods for evaluating the surface coordinates, first derivative s, and normal vectors of a NURB surface are compared. These methods in clude forward differencing, knot insertion, and a two-stage Cox-de Boo r technique. The computational complexity of each of these techniques is analyzed and summarized. The use of Hermite functions is shown to y ield a poor approximation for the shading functions of a NURB surface. An improved method for computing derivatives by knot insertion is pre sented. An efficient algorithm for computing the forward difference ma trix and a method for using forward differencing to compute the first derivatives of a NURB surface are also presented.