1. CNRS, Centrale Lille, UMR 9189 CRIStAL, University of Lille, Lille, France
2. IMT Nord Europe, Institut Mines-Télécom, Centre for Digital Systems, University Lille, Lille, France
3. Department of Information Engineering, University of Florence, Firenze, Italy
4. Robotics Institute, Carnegie Mellon University, Pittsburgh, PA, USA