1. An apparatus for sensing three-dimensional relative movement, the apparatus comprising: a movable motion sensor comprising a first and a second two-dimensional array of photo detectors; and at least one lens for directing far-field images onto the first and the second arrays of photo detectors, the sensor configured to generate digital representations of the far-field images and to generate three-dimensional relative movement data based on the digital representations of the far-field images, the movement data indicative of motion of the sensor in three dimensions.