1. Research Center “Enrico Piaggio” University of Pisa Largo Lucio Lazzarino 1 Pisa 56126 Italy
2. Computer Science and Artificial Intelligence Laboratory (CSAIL) Massachusetts Institute of Technology 32 Vassar Street Cambridge MA 02139 USA
3. Department of Information Engineering University of Pisa Via G. Caruso 16 Pisa 56122 Italy
4. Department of Mechanical and Aerospace Engineering University of Central Florida 12760 Pegasus Dr., Orlando FL 32816 USA
5. School of Biological and Health Systems Engineering Ira A. Fulton Schools of Engineering Arizona State University Tempe AZ USA
6. Istituto Italiano di Tecnologia Via Morego 30 Genoa 16163 Italy