ABSTRACT
NURBs curves and surfaces [11, 12] play important parts in computer aided geometric design. To increase the flexibility of the defining curve (or surface) basis, degree raising [6] and knot insertion [2, 5] are the most important tools to make different NURBs curves and surfaces compatible; i.e., they are of the same degree and are defined over the same knot sequence(s). Multiplication of splines is another important tool to combine two different NURBs curves or surfaces to one; i.e., they have common weight functions, which are the denominators of the rational B-splines.
