Patent ID: 8209117

Claim:
A method of navigation quality estimation, the method comprising: (a) obtaining an alignment observation; (b) comparing the alignment observation to a current heading estimate; (c) updating the current heading estimate based on the comparison; (d) updating a heading error estimate based on the updated current heading estimate; (e) determining an estimated drift rate based on the heading error estimate and an operational latitude, wherein the estimated drift rate is represented by a circular error probable rate that is calculated using the formula: CEPR= x*σ Heading *cos( y *abs(latitude)+ z ), wherein CEPR represents the circular error probable rate, σ heading represents the heading error estimate, abs(latitude) represents an absolute value of the operational latitude in degrees, and the x, y, z variables represent numerical values determined empirically and by interpolation of data; (f) determining if a drift rate requirement is met by the estimated drift rate; and (g) if the drift rate requirement is not met, repeating (a) to (f) until the drift rate requirement is met.