Specification of camera parameters for virtual keyboard

Virtual keyboards are commonly used as an on-screen input method in devices with no physical keyboard, where there is no room for one, such as a pocket computer, personal digital assistant (PDA), tablet computer or touch screen equipped mobile phone. The touch screen keyboard can be replaced in the near future with the virtual keyboard based on camera. We work on a project of such virtual keyboard, which is planned to be used in tablet. It means that the camera will capture an area under a relatively sharp angle. In our paper we analyze how the 3D space of a virtual keyboard is projected to the 2D view plane of camera, and we determine the limits of the camera parameters: camera elevation, angle of camera rotation, horizontal viewing angle.