1. Computer Science Department, Visualization Lab, University of Kaiserslautern, PO BOX 3049, D-67653, Kaiserslautern, Germany
2. School of Mathematics and Systems Engineering (MSI), Växjö University, Vejdes Plats 7, Växjö, SE-351 95, Sweden.
3. Competence Center Human-Centered Visualization (HCV), German Research Center for Artificial Intelligence, DFKI GmbH, Trippstadter Strasse 122, D-67663, Kaiserslautern, Germany