1 Introduction
In order to interact with virtual environments (VE), users often need to interactively position and orient objects or camera views. In order to do so, a lot of 6 degrees of freedom (DOF) input devices have been realized such as face trackers [6], [9], [13], nose trackers [5], hand trackers [11], [12], [14], magnetic trackers [2], [4] and other devices targeted more at the home user [1], [3]