1. Xsens Technologies B.V., Pantheon 6a, 7521 PR, Enschede, The Netherlands. E-mail: matteo.giuberti@xsens.com
2. Department of Information Engineering, University of Parma, Parco Area delle Scienze, I-43123, Parma, Italy. E-mail: gianluigi.ferrari@unipr.it