Navigation filter for navigation system by terrain matching.

The navigation filter (11) has a selectively tilting unit for calculating a kinematic state of a carrier and a covariance matrix, where the navigation filter restores values ??calculated by one of a convergence filter (21) e.g. particle filter or marginalised particle filter, and a tracking filter (22) e.g. extended Kalman filter or Unscented Kalman filter. The navigation filter restores the values based on the comparison of a quality index calculated from the covariance matrix restored by the navigation filter at one instant at a predetermined threshold value.