1. An apparatus comprising mobile part, the mobile part comprising: a first light emitter for forming a first light emission comprising a plurality of emitted rays on a cone or cylinder that is symmetrical about a central axis of the mobile part; and a first imager for acquiring images from a point of view along the central axis showing an illumination pattern at intersections of the emitted rays and a first surface upon which the first light emission impinges; wherein the apparatus further includes a first estimator for processing the acquired images and using the acquired images to determine at least one of (a) an orientation of the central axis of the apparatus with respect to the first surface, and (b) a distance from the surface along the central axis.