Gyrocompassing: From Gravity Rotation Analysis to Inertial Trajectory Fitting

<title>Abstract</title> Gyrocompassing is the process of using the rotation of the Earth to determine heading. This approach is the state-of-the-art solution when precise and robust heading is needed, such as in ship navigation. Currently, this procedure is performed using a high-grade inertial measurement unit, consisting of an accelerometer and a gyrometer. To circumvent parasitic motions from the ship, the Earth’s rotation is not directly measured by the gyrometer. The commonly adopted solution is to measure the rotation of the gravity vector in the inertial frame. A curated, straightforward method for gravity vector fitting based on singular value decomposition was developed here to provide a baseline algorithm. This method was compared with a second algorithm based on inertial trajectory fitting. Our results show how a trajectory-fitting algorithm can improve robustness and accelerate gyrocompassing compared with a traditional gravity analysis algorithm.