A positioning system , in particular a six dimensional positioning system, comprising: - a plurality of N light sources , wherein N is equal to at least four for at least one shadow sensor and N is equal to at least three for at least two shadow sensors ; - at least one shadow sensor configured to sense shadows cast on the shadow sensor by light emitted from the light sources , said shadow sensor comprising an imager ; - a processor configured to: - sync a shadow sensing with a pulsing of the light sources ; - distinguish between the sensed shadows from each of the light sources ; characterized in that - said shadow sensor comprises a mask , the mask having repetitive elements and a distinctive element, wherein as light from the light sources passes through the mask , a shadow of the mask is cast on the imager ; - the maximum distance between any of said light sources is larger than fifty times a width or a height of said imager ; and - the processor is configured to: - determine two dimensional positions of the shadows of the mask casted by each light sources on said imager ; and - compute a six dimensional position of the at least one shadow sensor with respect to the light sources based on the determined 2D positions, provided that the relative position of the light sources is known, wherein the six dimensional position of the shadow sensor is computed by considering the shadow sensor as a pinhole camera so as to use projective geometry computations. - a plurality of N light sources , wherein N is equal to at least four for at least one shadow sensor and N is equal to at least three for at least two shadow sensors ; - at least one shadow sensor configured to sense shadows cast on the shadow sensor by light emitted from the light sources , said shadow sensor comprising an imager ; - a processor configured to: - sync a shadow sensing with a pulsing of the light sources ; - distinguish between the sensed shadows from each of the light sources ; - sync a shadow sensing with a pulsing of the light sources ; - distinguish between the sensed shadows from each of the light sources ; - said shadow sensor comprises a mask , the mask having repetitive elements and a distinctive element, - the maximum distance between any of said light sources is larger than fifty times a width or a height of said imager ; and - the processor is configured to: - determine two dimensional positions of the shadows of the mask casted by each light sources on said imager ; and - compute a six dimensional position of the at least one shadow sensor with respect to the light sources based on the determined 2D positions, provided that the relative position of the light sources is known, wherein the six dimensional position of the shadow sensor is computed by considering the shadow sensor as a pinhole camera so as to use projective geometry computations. - determine two dimensional positions of the shadows of the mask casted by each light sources on said imager ; and - compute a six dimensional position of the at least one shadow sensor with respect to the light sources based on the determined 2D positions, provided that the relative position of the light sources is known, wherein the six dimensional position of the shadow sensor is computed by considering the shadow sensor as a pinhole camera so as to use projective geometry computations. <EOS>