1. Computer Vision Laboratory, ETH Zürich, Zürich, Switzerland
2. Computer Science Department, TU Darmstadt, Darmstadt, Germany,
3. UMIC Research Centre, RWTH Aachen, Aachen, Germany
4. Computer Vision Laboratory, ETH Zürich, Zürich, Switzerland and ESAT/PSI-VISICS IBBT, K.U. Leuven, Heverlee, Belgium