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Magnetometer Calibration for Portable Navigation Devices in Vehicles Using a Fast and Autonomous Technique

Using absolute navigation systems (such as global navigation satellite systems) has proved to be insufficient for indoor navigation or when navigating in urban canyons due to multipath and obstruction. This opened the gate widely for sensor-based navigation systems to be used, particularly after the development of low-cost microelectromechanical system sensors. Heading determination is one of the most important aspects for navigation solutions. Magnetometer is a low-cost sensor that can provide an absolute heading from magnetic north by sensing the Earth's magnetic field. Magnetometer readings are usually affected by magnetic fields, other than the Earth's magnetic field, and by other error sources; therefore, magnetometer calibration is required. In this paper, a technique is proposed for fast and automatic magnetometer calibration that requires small space coverage. There is no user involvement in the calibration process, and there are no required specific movements. The proposed technique performs 3-D-space magnetometer calibration using 2-D calibration equations with pitch and roll sectors. The 3-D-space is divided into a group of pitch and roll sectors. Inside each sector, 2-D calibration can be performed for the leveled magnetometer readings, which make the calibration process faster and requiring less data. This technique makes the magnetometer useful for determining heading in pseudo-tethered devices, particularly when used while driving. Pseudo-tethered navigation devices are tethered at normal operation, but they can change their orientation according to user needs such as portable vehicle navigation devices, which can be placed on the dashboard of a vehicle or attached to the wind shield.