A six degrees of freedom positioning system comprising: - a target comprising N light sources; - at least one shadow sensor comprising a mask and configured to sense shadows cast on the shadow sensor by light emitted from the light sources of the target, wherein N is equal to at least four for one shadow sensor and N is equal to at least three for at least two shadow sensors with known relative position; and - a processor (108, 800); wherein the processor (108, 800) is configured to: - recording a projection of at least four points, a projection of a point being a projection of light from a light source of the target on the shadow sensor; characterized in that the processor is further configured for: - computing a first estimate of the six degrees of freedom position of the target with respect to the shadow sensor using known prior six degrees of freedom positions or a computation method and provided that the relative positions of the light sources are known; - virtually reprojecting from said first estimate of the six degrees of freedom position the at least four points on the shadow sensor by considering the shadow sensor as a calibrated pinhole camera (302, 304) so as to use projective geometry computations; - computing an error between the recorded projections and the virtual reprojections; - estimating the six degrees of freedom position of the target with respect to the shadow sensor based on said error and on said first estimate of the six degrees of freedom position of the target. - a target comprising N light sources; - at least one shadow sensor comprising a mask and configured to sense shadows cast on the shadow sensor by light emitted from the light sources of the target, wherein N is equal to at least four for one shadow sensor and N is equal to at least three for at least two shadow sensors with known relative position; and - a processor (108, 800); wherein the processor (108, 800) is configured to: - recording a projection of at least four points, a projection of a point being a projection of light from a light source of the target on the shadow sensor; characterized in that the processor is further configured for: - computing a first estimate of the six degrees of freedom position of the target with respect to the shadow sensor using known prior six degrees of freedom positions or a computation method and provided that the relative positions of the light sources are known; - virtually reprojecting from said first estimate of the six degrees of freedom position the at least four points on the shadow sensor by considering the shadow sensor as a calibrated pinhole camera (302, 304) so as to use projective geometry computations; - computing an error between the recorded projections and the virtual reprojections; - estimating the six degrees of freedom position of the target with respect to the shadow sensor based on said error and on said first estimate of the six degrees of freedom position of the target. - recording a projection of at least four points, a projection of a point being a projection of light from a light source of the target on the shadow sensor; characterized in that the processor is further configured for: - computing a first estimate of the six degrees of freedom position of the target with respect to the shadow sensor using known prior six degrees of freedom positions or a computation method and provided that the relative positions of the light sources are known; - virtually reprojecting from said first estimate of the six degrees of freedom position the at least four points on the shadow sensor by considering the shadow sensor as a calibrated pinhole camera (302, 304) so as to use projective geometry computations; - computing an error between the recorded projections and the virtual reprojections; - estimating the six degrees of freedom position of the target with respect to the shadow sensor based on said error and on said first estimate of the six degrees of freedom position of the target.