1. Electro-optical system for determining position and orientation of a mobile part, said system comprising a fixed part comprising projection means and having a centre of projection and a mobile part, the fixed part being linked rigidly with a virtual image plane, the mobile part being linked rigidly with at least two linear electro-optical devices, the projection means projecting into a zone comprising the electro-optical devices, at least two networks of beams, whose intersection with the image plane defines at least two networks of nonparallel straight lines, each of the networks of straight lines comprising at least three parallel segments, each of the electro-optical devices being intercepted at least two triples of points, wherein the two electro-optical devices being coplanar and their direction secant, the orientation and the position of the mobile part is determined as a function of the vanishing points (E, F) in the image plane of the two straight lines respectively comprising the first and the second electro-optical devices, calculation means making it possible, on the basis of the points of intersections of the beams on the electro-optical devices, to determine the positions: of the projections on the image plane of a first triple (A, I, B) of points whose positions are known in a benchmark frame linked with the first device; of the projections on the image plane of a second triple of points (C, J, G) whose positions are known in a benchmark frame linked with the second devices; and of the vanishing points (E, F) in the image plane.