A terminal to calculate a position and detect spoofing, the terminal includes a receiver of first signals, notably signals of a GNSS type, from first sources, to compute a first information relative to its position, as for instance a pseudo range measurement, an ephemeris, a navigation message, spatial coordinates or temporal coordinates, and to calculate a position; a receiver of a second signal of a non-RF and non-GNSS type from a second source, notably from an optical display, the second signal comprising a second information transmitted using a predetermined encoding format to retrieve said second information; a processing logic configured to detect spoofing by comparing the first and second information. The associated transmitters, authentication server and spoofing detection methods are also provided.