1. An interface for producing an input from an absolute pose of an item associated with a user in a three-dimensional environment, said interface comprising: a) a unit on-board said item, said unit configured to receive non-collinear optical inputs presented by at least one stationary object in said three-dimensional environment, said at least one stationary object having at least one feature detectable via an electromagnetic radiation, said at least one feature presenting a sufficient number of said non-collinear optical inputs for establishing a stable frame in said three-dimensional environment; b) processing electronics employing a computer vision algorithm using a homography to recover said absolute pose of said item from a geometrical description of said non-collinear optical inputs in terms of absolute pose parameters in said stable frame and to generate a signal related to at least one of said absolute pose parameters; c) an application employing said signal in said input, wherein said absolute pose of said item comprises at least three translational degrees of freedom and at least three rotational degrees of freedom, said at least one absolute pose parameter is related to at least one among said at least three translational degrees of freedom and said at least three rotational degrees of freedom by a mapping and at least one aspect of said application varies with said absolute pose of said item.