Screw pole, suitable to be installed along the sides of a railway line for the execution of topographic surveys aimed at detecting and verifying the track layout (Bl) of the railway line, comprising: - a stem, threaded, allowing to screw (f) the screw pole into the ground in the area of or adjacent to the ballast, that is to the gravel embankment of the railway line; and - coupling and fixing means (12, 12a), associated with an upper end of said stem, for coupling and fixing to the screw pole, once screwed into the ground at the sides of the railway line, an optical measuring device or tool, defining a reference point, included in and part of a wider optical measurement system to measure and detect the topographical track layout (Bl) of the railway line; wherein said coupling and fixing means comprise an upper plate, fixed to, extended transversely and protruding from said upper end of said stem; wherein said upper plate has a plurality of slots corresponding to a plurality of corresponding pegs, each having a stem of smaller diameter and a head (22a") of greater diameter, projecting from a lower plate of said optical measuring device or tool; wherein said plurality of slots, of the screw pole, are adapted to cooperate with said plurality of corresponding pegs of the optical measuring device or tool, by inserting the pegs in the slots and then rotating the optical measuring device or tool with respect to the screw pole, so as to couple and fix the optical measuring device or tool to the screw pole screwed into the ground at the sides of the railway line; and wherein each of said slots has a wider portion and a narrower portion (12a"); whereby each peg, protruding from the lower plate of the optical measuring device or tool, is able to be inserted with its head (22a"), of greater diameter, in the wider portion of the corresponding slot, formed in the upper plate of the screw pole, and then to cooperate with its stem, of smaller diameter, with the narrower portion (12a") of the same slot, when the optical measuring device or tool is rotated with respect to the screw pole in order to connect these two parts to each other. - a stem, threaded, allowing to screw (f) the screw pole into the ground in the area of or adjacent to the ballast, that is to the gravel embankment of the railway line; and - coupling and fixing means (12, 12a), associated with an upper end of said stem, for coupling and fixing to the screw pole, once screwed into the ground at the sides of the railway line, an optical measuring device or tool, defining a reference point, included in and part of a wider optical measurement system to measure and detect the topographical track layout (Bl) of the railway line; wherein said coupling and fixing means comprise an upper plate, fixed to, extended transversely and protruding from said upper end of said stem; wherein said upper plate has a plurality of slots corresponding to a plurality of corresponding pegs, each having a stem of smaller diameter and a head (22a") of greater diameter, projecting from a lower plate of said optical measuring device or tool; wherein said plurality of slots, of the screw pole, are adapted to cooperate with said plurality of corresponding pegs of the optical measuring device or tool, by inserting the pegs in the slots and then rotating the optical measuring device or tool with respect to the screw pole, so as to couple and fix the optical measuring device or tool to the screw pole screwed into the ground at the sides of the railway line; and wherein each of said slots has a wider portion and a narrower portion (12a"); whereby each peg, protruding from the lower plate of the optical measuring device or tool, is able to be inserted with its head (22a"), of greater diameter, in the wider portion of the corresponding slot, formed in the upper plate of the screw pole, and then to cooperate with its stem, of smaller diameter, with the narrower portion (12a") of the same slot, when the optical measuring device or tool is rotated with respect to the screw pole in order to connect these two parts to each other.