1. A method of obtaining positional data of at least one region of reflectivity contained in a field of view, said field of view containing a plurality of said regions of reflectivity, said method comprising the steps of: projecting into said field of view at least two detectable markers ( 107 ), each marker ( 107 ) produced by incidence of at least one electromagnetic beam ( 106 ) on at least reference plane comprised by said field of view, said reference plane comprising at least one region of reflectivity, said beams ( 106 ) having at least one origin ( 1109 ); and capturing an image of said field of view and said markers ( 107 ) on an image plate ( 501 ), said method characterised by comprising the steps of: selecting a set of beam configuration characteristics, wherein at least one spatial relationship between at least one of the origins ( 1109 ) of said beams ( 106 ) and said image plate ( 501 ), at image capture, is determined, identifying at least two markers ( 107 ) in the captured image; and using said at least one spatial relationship to determine a set of offset values relating said image plate to said origin(s) ( 1109 ); and using the identification of said markers, said offset values, said selected beam configuration characteristics and trigonometric calculations to determine a set of orientation values describing the orientation of said image plate to each of selected regions of reflectivity in the field of view, said selected regions of reflectivity not being comprised by said reference plane.