Method and arrangement for determining the trajectory on a map which corresponds to the trajectory actually travelled by a mobile system

A vehicle navigation system comprises a GPS (220), gyroscope (230) and odometer (240). At regular intervals on a journey using the GPS and the odometer a vehicle actual first position is determined, whilst, with the GPS, system a second or redundant position is determined. Each a is used to derive a plan of the actual route traversed. These are then compared using a specific comparison criterium to derive the route traversed most closely corresponding to that actually traversed.