Patent ID: 8594927

Claim:
A navigation filter for a terrain aided navigation system, the navigation filter delivering an estimation of a kinematic state of a carrier craft associated with a covariance matrix at a discretized moment in time k, the navigation filter comprising: measurements returned by at least one terrain sensor, a model associated with the at least one terrain sensor, data from an onboard map, an error model for the onboard map, measurements returned by an inertial guidance system, a model of the inertial guidance system, a convergence filter, and a tracking filter, the navigation filter further comprising switch-over means for selecting, for calculation of the estimation of the kinematic state of the carrier craft and of the covariance matrix, one or more of the convergence filter and the tracking filter, based on comparison of a quality index calculated from the covariance matrix at a preceding time k−1 with a predetermined threshold value, the navigation filter returning values calculated by the selected one or more of the convergence filter and the tracking filter.