B-spline curves - clipping and 3d primitives

B-spline curves are piecewise polynomial cubes with one or more polynomial pieces with a minimum smoothness requirement.  For example, a C² cubic B-spline curve has one or more cubic pieces which are joined in such a way that the resulting composite curve is twice continuously differentiable.   B-spline curves have a very elegant expression similar to the Bezier representation with basis function as B-spline functions in place of Bernstein basis polynomials.  B-spline basis functions can be computed iteratively using de Boor algorithm.