Efficient Trimmed NURBS Tessellation

Interactive rendering of trimmed NURBS models is of great importance for CAD systems. For this the model needs to be transformed into a polygonal representation. This transformation can be either performed in a preprocessing step, at the cost of losing the capability to edit the surfaces, or on the fly during rendering. Since the number of frames per second is usually critical, efficient on the fly tessellation of trimmed NURBS surfaces is very important for interactive rendering and editing of such models. In this paper we present an efficient – with respect to both runtime and to the number of generated triangles – tessellation algorithm for trimmed NURBS surfaces that is capable of guaranteeing a specified geometric approximation error. When affordable by the subsequent steps in the pipeline, an approximate error of the tessellation can also be used leading to fewer triangles.