1. VISUS, Universitat Stuttgart, 9149 Stuttgart, Baden-Wrttemberg, Germany, 70569
2. Lawrence Livermore National Laboratory, 4578 Livermore, California, United States
3. Institut fuer Visualisierung und Interaktive Systeme, Universitaet Stuttgart, Stuttgart, BW, Germany, 70569
4. Computer and Information Science, University of Oregon, Eugene, Oregon, United States
5. Bernoulli Institute of Mathematics, Computer Science and Artificial Intelligence, University of Groningen, 3647 Groningen, Groningen, Netherlands, 9700 AB