1. A position detection system for detecting a three dimensional position of plurality of targets, including: the plurality of targets, wherein each target is configured to act as a retro-reflector for light incident from any direction; a plurality of detectors configured to detect and take measurements of light retro-reflected from the targets, individual targets of the plurality of targets being surrounded by at least a subset of the plurality of detectors; at least one light emitter for illuminating the targets, the or each light emitter being for illuminating a plurality of the targets and including a diverging element, the diverging element being configured to direct the light from a light source to the plurality of targets and direct the light retro-reflected by at least one of the plurality of targets to at least one of the plurality of detectors; and a processor configured to process measurements taken simultaneously by individual detectors of the plurality of detectors to determine the three dimensional position of the targets using absolute distance measurements determined from measurements from the at least one detector using frequency scanning interferometry.