NURBS rendering in OpenSG Plus

Most of the industrial parts are designed as trimmed NURBS. Today’s graphics hardware supports the high-speed display of polygonal objects consisting of triangles. This means that analytical surfaces (like NURBS) need to be triangulated so they can be displayed by 3D graphics cards. To be able to control the quality of the tesselated model, the triangulation should be carried out with a given error torelance. Currently available methods make it possible to achieve approximation of the surface in 3D space with a given error and to polygonize the trimming curves with another given error, but only in the parameter space of the surface. From this fact follows that there exists no error control of the trimming curves in Euclidean space, which can result in cracks along the trimming curves in case of models consisting of more than one surface and models usually consist of several hundreds or thousands of surfaces. Our new method introduced in this paper takes care of this problem, i.e. it can guarantee the geometric error along the trimming curves. This makes also possible to sew these surfaces together along their borders. Several examples of industrial data 1 demonstrate the applicability of our new method. The introduced techniques will also be included into the OpenSG scenegraph API as the basic tool for NURBS rendering.