The authors would like to thank those persons who contributed with their concepts and implementations to the work presented in this paper: Torsten Sommerfeld (figure captions for anatomic illustrations), Alf Ritter, Michael Rüger and Andreas Raab (zoom techniques in 2D and 3D). Moreover, we wish to thank Rainer Michel for fruitful discussions; he also incorporated figure captions for computer generated maps for blind people. Finally, we wish to thank Brigitte Grote for a thorough reading and many suggestions to improve the paper.