Efficient NURBS Rendering using View-Dependent LOD and Normal Maps

Rendering large trimmed NURBS models with high quality at interactive frame rates is of great interest for industry, since nearly all their models are designed on the basis of this surface type. Most existing approaches transform the NURBS surfaces into polygonal representation and build static levels of detail. Unfortunately, algorithms which keep the NURBS representation and generate view-dependent LOD on the fly suffer from the problem, that they only calculate the geometric error of an approximation, but no care is taken of the illumination artefacts introduced by the chosen view-dependent triangulation. Normal maps have proven to be very accurate in providing better visual quality without increasing the complexity of the geometry itself and thus solving this problem, but need much memory to store the normal textures. In this paper we present a novel approach to apply normal maps to view-depandent NURBS rendering with small memory and computational overhead. Additionally, we apply our approach to render isophotes and environment maps such as reflection lines on view dependent triangulations with high visual fidelity.