1. German Aerospace Center (DLR), 12489 Berlin, Germany
2. Visual Computing Lab, Information Technologies Institute, Centre for Research and Technology Hellas (CERTH), 57001 Thermi, Greece
3. Señales, Sistemas y Radiocomunicaciones, ETSI Telecomunicación, Universidad Politécnica de Madrid (UPM), 28040 Madrid, Spain
4. German Aerospace Center (DLR), 82234 Wessling, Germany
5. CS2 Research Centre, School of Computing and Mathematical Sciences, University of Greenwich, London SE10 9LS, UK