A system for detecting a position of an object such as a surgical tool inan image guidance system includes a camera system with a detection array fordetecting visible light a processor arranged to analyze the output from thearray.Each object to be detected carries a single marker with a pattern ofcontrasted areasof light and dark intersecting at a specific single feature point thereon. Thepatternincludes components arranged in an array around the specific location arrangedsuch that the processor is able to detect an angle of rotation of the patternaroundthe location and which are different from other markers of the system suchthat theprocessor is able to distinguish each marker from the other markers.
