“…For example, recent interactive systems attempt to detect user intents expressed in the form of gestures or voice commands using signals from various sensing devices [ 1 , 2 , 3 ]. More immersive and natural ways to capture user intent include face orientation estimation [ 4 , 5 , 6 ], body tracking [ 7 , 8 , 9 ], and estimation of gaze direction [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. For example, the authors of [ 4 , 5 , 6 ] proposed to estimate a driver’s face orientation with color or depth images taken in a specific environment, such as a vehicle, with the aim of preventing traffic accidents.…”