In the praxis of cutting glass many problems related to geometric modelling arise. At first some points on the actual glass are sampled and the surface model is calculated. Now patterns on this surface are designed and a photorealistic image of the final result is computed. By an analysis of the curvature it is possible to decide whether a cut is feasible with the given tools. In the following the path of the cutting tool is computed an, if necessary, modified corresponding to the actual position and outline of the real glass.