This work was supported in part by the Bavarian Ministry for Economic
Affairs and the European Fund for Regional Development. Corresponding
author: B. M. Eskofier (eskofier@cs.fau.de)
1S. Gradl, P. Kugler and B. M. Eskofier are with the Digital Sports
Group, Pattern Recognition Lab, Computer Science Department, Friedrich-
Alexander University of Erlangen-Nuremberg, Germany.
2C. Lohm¨uller is with the Department of Surgery, University Hospital
Erlangen, Germany.