GM_Knot is used to control the constructive parameter space for spline curves and surfaces. Each knot sequence is used for a dimension of the spline's parameter space. Thus, in a surface spline, there will be two knot sequences, one for each parameter (u, v). The ith, jth would be (ui, vj), where the original knot sequences were (ui) and (vj). Each knot of a spline curve or surface is described using a GM_Knot. <br/>