Point location method for a vehicle moving on a constrained trajectory and associated system

A point location method for a vehicle moving on a constrained trajectory of known route, said method making it possible to detect the point of passage of the vehicle closest to a predetermined position and being implemented by a location device performing measurements of distance and of speed of the vehicle along the trajectory, and at least one geopositioning receiver receiving positioning signals from at least one satellite of a satellite geopositioning system, and comprising a local time base measuring the current time, synchronized to the time of said satellite geopositioning system, said method comprising:

• a step Etp0, during which use is made of the information on speed and position of the vehicle on its trajectory, supplied by the location device, to estimate, at the current time, the moment of passage closest to said predetermined position (Tcpa) by taking account of the uncertainties on the time base of the location device;
• a step Etp1, during which several possible moments of passage of the vehicle closest to the predetermined position are estimated, said possible moments being located around the estimated moment of passage closest to said predetermined position (Tcpa);
• a step Etp2, during which the estimation of the possible positions of the vehicle on the trajectory is performed for each of the possible moments of passage closest to the predetermined position, by taking account of the uncertainties on speed of the vehicle and on position on the trajectory estimated at the current time and extrapolated to the estimated moment of passage of the vehicle closest to the predetermined position (Tcpa), said possible positions being included in a range of positions centred on the predetermined positon;
• a step Etp3, during which a prediction is made, for each of said possible positions, as to the form of a set of satellite geopositioning signals corresponding to the set of geopositioning signals expected for this position at the corresponding moment;
• a step Etp4, during which, for each possible moment of passage of the vehicle closest to the predetermined position, the spatial match between the expected geopositioning signals and those received by the geopositioning receiver at the current time is tested, by suitable filtering;
• the estimated possible position for which the match is maximal being considered as the point of passage closest to the predetermined position and the corresponding current time as the moment of passage closest to the determined position.