Land navigation system displaying the position of a vehicle in real time

Claim 1

A land navigation system for a vehicle having a position and a direction and adapted to travel at a distance from a reference position, for displaying the position of the vehicle in real time, said system comprising: sensor means (1) for preparing signals representing parameters of movement of the vehicle, including at least information on the distance travelled from the reference position, and information on the direction of the vehicle; means for processing and digitalization (2) of the signals from the sensor means; first computation means (3) for periodic computation using said digitalized signals, of an estimated position (M) of the vehicle; first random-access memory storage means (4) for storing the successive estimated positions and for an estimated trajectory (TE) of the vehicle; a mass memory (5) forming a digital cartographic data base comprising point by point description of routes; a reader (6) connected to the mass memory to extract therefrom the cartographic data corresponding to a selected zone chosen to include the estimated position of the vehicle and to give information on each point of the routes in the selected zone; second random-access memory (7) storage means, for storing the data of the selected zone extracted by the reader; a central processing unit (8) for management and computation, to coordinate the land navigation system according to a preestablished programming; a display device (11, 12) to display in image of the selected zone as well as the position of the vehicle; and a device (12A) to designate any point of the displayed image, wherein, to enable the automatic readjustment of the estimated trajectory at a readjustment point, the central processing unit comprises means for comparing the information on direction form the sensor means with information on direction extracted form the mass memory in the selected zone, within an imprecision zone centered on the estimated position of the vehicle, the comparison consisting in finding points, in the imprecision zone, for which at least the vehicle direction is substantially the same as the information on direction at a given instant, said comparison being continued until only one point is found in the imprecision zone, and this only found point forming the readjustment point; and wherein the position of the vehicle, displayed by the display device (11, 12) is the last position of the vehicle, whether it is obtained by the first computation means or by said automatic readjustment.