System and method for calibrating a magnetometer on a mobile device

1. A method of calibrating a magnetometer on a mobile device, the method comprising:

obtaining one or more pairs of magnetometer readings, each pair including a first reading and a second reading;

for each pair of magnetometer readings:

determining a rotation axis direction and a rotation angle corresponding to a change in orientation of the mobile device between obtaining the first reading and the second reading; and

determining a rotation axis for the pair of magnetometer readings using the rotation axis direction and rotation angle; and

determining a calibration parameter based on at least one property of one or more rotation axes.

2. The method of claim 1 , wherein for each pair of magnetometer readings, an angle between the first reading and the second reading about the rotation axis corresponds to the rotation angle.

3. The method of claim 1 , wherein for each pair of magnetometer readings, at least one of the rotation axis direction or the rotation angle is obtained using a gyroscope reading.

4. The method of claim 1 , wherein determining the calibration parameter comprises determining a point of a minimum distance between two or more rotation axes.

5. The method of claim 1 , further comprising determining a cluster comprising a plurality of points indicative of proximity between two or more rotation axes.

6. The method of claim 1 , further comprising:

determining location information of the mobile device;

obtaining expected magnetic field data based on the location information; and

determining the calibration parameter using the expected magnetic field data.

7. The method of claim 6 , wherein for each pair of magnetometer readings, an angle between the first reading and the second reading about the rotation axis corresponds to the rotation angle.

8. The method of claim 6 , wherein for each pair of magnetometer readings, at least one of the rotation axis direction or the rotation angle is obtained using a gyroscope reading.

9. The method of claim 6 , wherein the calibration parameter is a point on the rotation axis.

10. The method of claim 6 , wherein the expected magnetic field data comprises at least one of an expected magnitude of a magnetic field or an expected inclination angle.

11. The method of claim 6 , wherein the expected magnetic field data is obtained from a predetermined set of magnetic field data arranged according to location.

12. The method of claim 6 , wherein the expected magnetic field data is obtained by performing a predetermined set of computations using the location information.

13. A non-transitory computer readable storage medium for calibrating a magnetometer on a mobile device, the computer readable storage medium comprising computer executable instructions that when executed by a processor cause the processor to perform operations comprising:

obtaining one or more pairs of magnetometer readings, each pair including a first reading and a second reading;

for each pair of magnetometer readings:

determining a rotation axis direction and a rotation angle corresponding to a change in orientation of the mobile device between obtaining the first reading and the second reading; and

determining a rotation axis for the pair of magnetometer readings using the rotation axis direction and rotation angle; and

determining a calibration parameter based on at least one property of one or more rotation axes.

14. The non-transitory computer readable storage medium of claim 13 , wherein for each pair of magnetometer readings, an angle between the first reading and the second reading about the rotation axis corresponds to the rotation angle.

15. The non-transitory computer readable storage medium of claim 13 , wherein for each pair of magnetometer readings, at least one of the rotation axis direction or the rotation angle is obtained using a gyroscope reading.

16. The non-transitory computer readable storage medium of claim 13 further comprising computer executable instructions for:

determining location information of the mobile device;

obtaining expected magnetic field data based on the location information; and

determining the calibration parameter using the expected magnetic field data.

17. A mobile device comprising a processor coupled to a non-transitory memory, a magnetometer and a gyroscope, the non-transitory memory comprising computer executable instructions that when executed by the processor cause the processor to perform operations comprising:

obtaining one or more pairs of magnetometer readings, each pair including a first reading and a second reading;

for each pair of magnetometer readings:

determining a rotation axis direction and a rotation angle corresponding to a change in orientation of the mobile device between obtaining the first reading and the second reading; and

determining a rotation axis for the pair of magnetometer readings using the rotation axis direction and rotation angle; and

determining a calibration parameter based on at least one property of one or more rotation axes.

18. The mobile device of claim 17 , wherein for each pair of magnetometer readings, an angle between the first reading and the second reading about the rotation axis corresponds to the rotation angle.

19. The mobile device of claim 17 , wherein for each pair of magnetometer readings, at least one of the rotation axis direction or the rotation angle is obtained using a gyroscope reading.

20. The mobile device of claim 17 , wherein the non-transitory memory further comprises computer executable instructions for:

determining location information of the mobile device;

obtaining expected magnetic field data based on the location information; and

determining the calibration parameter using the expected magnetic field data.