TURBS—Topologically Unrestricted Rational B-Splines

We present a new approach to the construction of piecewise polynomial or rational C ^k -spline surfaces of arbitrary topological structure. The basic idea is to use exclusively parametric smoothness conditions, and to solve the well-known problems at extraordinary points by admitting singular parametrizations. The smoothness of the spline surfaces is guaranteed by specifying a regular smooth reparametrization explicitly. The resulting space of topologically unrestricted rational B-splines (TURBS) is linear and possesses a natural refinement property. Compared with all known methods the construction principle of TURBS is of striking simplicity and the required polynomial bi-degree is essentially decreased from O(k ² ) to d=2k+2 . January 5, 1996. Date revised: September 5, 1996.