Provided is a mobile device including a magnetic sensor and a posture detection sensor for detecting a posture of the mobile device independently of the magnetic sensor, which acquires output data of the magnetic sensor as a plurality of sampling data items in a plurality of states in which the posture detection sensor determines that the mobile device is directed in directions different from one another, the plurality of sampling data items respectively corresponding to the plurality of states, and calculates an offset value which is estimated to be output by the magnetic sensor when the magnetic sensor is not sensing geomagnetism based on the acquired plurality of sampling data items.
1. A mobile device comprising:
a magnetic sensor;
a posture detection sensor for detecting a posture of the mobile device independently of the magnetic sensor;
a sampling data acquisition section for acquiring output data of the magnetic sensor as a plurality of sampling data items in a plurality of states in which the posture detection sensor determines that the mobile device is directed in directions different from one another, the plurality of sampling data items respectively corresponding to the plurality of states;
an offset value calculation section for separately calculating a respective offset value for each of a plurality of orthogonal reference axes of the magnetic sensor, which are estimated to be output by the magnetic sensor when the magnetic sensor is not sensing geomagnetism based on the acquired plurality of sampling data items; and
a storage unit for storing the respective offset values,
wherein the offset value calculation section separately calculates a new offset value and evaluates a reliability of the new offset value, and updates a corresponding one of the offset values stored in the storage unit in accordance with the reliability of the new offset value such that: (i) when the reliability of the new offset value is high, the corresponding one of the offset values stored in the storage unit is replaced with the new offset value, and (ii) when the reliability of the new offset value is low, the corresponding one of the offset values stored in the storage unit is changed toward, but not replaced by, the new offset value.
2. The mobile device according to claim 1 , wherein the sampling data acquisition section acquires the plurality of sampling data items in a plurality of states in which the posture detection sensor determines that the mobile device is directed in directions different from one another by a predetermined angle or larger, the plurality of sampling data items respectively corresponding to the plurality of states.
3. The mobile device according to claim 1 , wherein the offset value calculation section evaluates the reliability of the newly calculated offset value based on the offset value which has been stored and the newly calculated offset value.
4. The mobile device of claim 1 , wherein the offset value calculation section evaluates the reliability of the new offset value by evaluating a difference between the new offset value and the corresponding one of the offset values stored in the storage unit, whereby a higher difference indicates a lower reliability and a lower difference indicates a higher reliability.
5. The mobile device of claim 1 , wherein the offset value calculation section evaluates the reliability of the new offset value by evaluating a difference between a measured orientation of the mobile device using the new offset value and a measured orientation of the mobile device using the posture detection sensor, whereby a higher difference indicates a lower reliability and a lower difference indicates a higher reliability.
6. A calibration method for a magnetic sensor for a mobile device including the magnetic sensor and a posture detection sensor for detecting a posture of the mobile device independently of the magnetic sensor, the calibration method comprising:
acquiring output data of the magnetic sensor as a plurality of sampling data items in a plurality of states in which the posture detection sensor determines that the mobile device is directed in directions different from one another, the plurality of sampling data items respectively corresponding to the plurality of states;
separately calculating a respective offset value for each of a plurality of orthogonal reference axes of the magnetic sensor, which are estimated to be output by the magnetic sensor when the magnetic sensor is not sensing geomagnetism based on the acquired plurality of sampling data items; and
storing the respective offset values in a storage unit,
wherein the calculating step includes separately calculating a new offset value and evaluating a reliability of the new offset value, and updating a corresponding one of the offset values stored in the storage unit in accordance with the reliability of the new offset value such that: (i) when the reliability of the new offset value is high, the corresponding one of the offset values stored in the storage unit is replaced with the new offset value, and (ii) when the reliability of the new offset value is low, the corresponding one of the offset values stored in the storage unit is changed toward, but not replaced by, the new offset value.
7. A non-transitory computer-readable information storage medium having a calibration program stored thereon, the calibration program being used for a magnetic sensor for a mobile device including the magnetic sensor and a posture detection sensor for detecting a posture of the mobile device independently of the magnetic sensor, the calibration program including instructions that cause a computer to:
acquiring output data of the magnetic sensor as a plurality of sampling data items in a plurality of states in which the posture detection sensor determines that the mobile device is directed in directions different from one another, the plurality of sampling data items respectively corresponding to the plurality of states; and
separately calculating a respective offset value for each of a plurality of orthogonal reference axes of the magnetic sensor, which are estimated to be output by the magnetic sensor when the magnetic sensor is not sensing geomagnetism based on the acquired plurality of sampling data items; and
storing the respective offset values in a storage unit,
wherein the calculating step includes separately calculating a new offset value and evaluating a reliability of the new offset value, and updating a corresponding one of the offset values stored in the storage unit in accordance with the reliability of the new offset value such that: (i) when the reliability of the new offset value is high, the corresponding one of the offset values stored in the storage unit is replaced with the new offset value, and (ii) when the reliability of the new offset value is low, the corresponding one of the offset values stored in the storage unit is changed toward, but not replaced by, the new offset value.