1. A system comprising: a 3-D imaging system that generates a 3D depth image of a user in the field-of-imaging (FOI) of said imaging system, the 3-D imaging system uses Time of Flight (TOF) 3-D imaging, the 3D system identifies at least a first point and a second point based on the 3D depth image, the first point is an eye, the 3D system generates continuous data of the spatial position of the first point and the second point based on the 3D image; and a computation system that calculates a pointing line extending from said first point through said second point towards a screen based on the continuous data of the spatial positions, the computation system calculates an imaginary point on said screen at which said pointing line hits said screen.