Using the geometric information intrinsic to NURBS allows some precalculations. Surface normals are view-independent and can be precalculated, given that it is known which normals one will need. As stated in Section 3.1, in order to imitate the edge lines used in technical illustration for a NURBS model, surface boundaries and discontinuities, as well as silhouettes, need to be drawn. In Section 4.1.1, I will discuss how to find boundaries and discontinuities for NURBS surfaces. In Section 4.1.2, I will define some algorithms for finding silhouettes on NURBS surfaces.