1. UMR LETG CNRS 6554, University of Rennes, Rennes, France
2. Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, the Netherlands
3. Faculty of Computer Science and Mathematics, Bremen Spatial Cognition Centre, University of Bremen, Bremen, Germany
4. UMR Espace-Dev, IRD, University of Montpellier, Montpellier, France