Radiographic imaging system, comprising; an emission unit (2) for emitting X rays; a reception unit (3) for receiving X rays; and a plate (11) made from a material which is opaque to X rays and which is situated between the emission unit (2) and the reception unit (3), the plate (11) comprising at least four channels (20 to 23), each channel allowing a part of the X rays emitted by the emission unit (2) to pass through the channel; and an image processing unit (4) configured to determine the co-ordinates of the projected patterns (M1 to M4) and to calculate a position of the reception unit (3) on the basis of the co-ordinates of the projected patterns (M1 to M4) and of the co-ordinates of the channels (20 to 23).