1. a Computer Vision and Machine Intelligence Laboratory, Aalborg University, DK-3750 Ballerup, Denmark;, Email: vok@cvmi.aau.dk
2. b Computer Vision and Active Perception Laboratory, CSC-KTH, SE-10044 Stockholm, Sweden
3. c Jozef Stefan Institute, Department of Automatics, Biocybernetics & Robotics, 1000 Ljubljana, Slovenia
4. d School of Informatics, University of Edinburgh, Edinburgh, EH8 9LE UK