A markerless tracking device comprising a source configured to direct a beam on a plurality of beam paths, where each beam path illuminates a distinct region of an object; a sensor configured to receive beam reflected from each region in order to generate an image of each region; and a processor configured to generate a metric which indicates suitability of a beam trajectory, wherein the metric is generated by comparing images of selected regions, and wherein the beam trajectory is a path over which the beam is to be directed by the source during markerless tracking of the object.