System and Method for Calibrating a Magnetometer Using Partial and Full Calibrations

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

obtaining a plurality of magnetometer sensor readings;

storing sensor readings from the plurality of obtained sensor readings that are different;

determining a first calibration parameter based on a first predetermined number of different readings; and

determining a plurality of calibration parameters based on a second predetermined number of different readings, wherein the plurality of calibration parameters includes the first calibration parameter.

2 . The method according to claim 1 , further comprising:

applying at least one test to the plurality of calibration parameters; and

accepting the plurality of calibration parameters as an active set of calibration parameters if the plurality of calibration parameters are acceptable according to the at least one test.

3 . The method according to claim 1 , wherein the first predetermined number of different readings comprises enough values to compute a constant bias along each axis of the magnetometer.

4 . The method according to claim 3 , wherein at least 3 different readings are required to determine the first calibration parameter.

5 . The method according to claim 1 , wherein the second predetermined number of different readings comprises enough values to compute constant bias, gain, and inter-axis misalignment parameters along each axis of the magnetometer.

6 . The method according to claim 5 , wherein at least 9 different readings are required to determine the plurality of calibration parameters.

7 . The method according to claim 1 , further comprising determining a radius of a sphere representing a magnetic field using the first predetermined number of different readings.

8 . The method according to claim 1 , wherein the plurality of calibration parameters are determined using a least squares fitting algorithm.

9 . A computer readable medium comprising computer executable instructions for calibrating a magnetometer on a mobile device, the computer executable instructions comprising instructions for:

obtaining a plurality of magnetometer sensor readings;

storing sensor readings from the plurality of obtained sensor readings that are different;

determining a first calibration parameter based on a first predetermined number of different readings; and

determining a plurality of calibration parameters based on a second predetermined number of different readings, wherein the plurality of calibration parameters includes the first calibration parameter.

10 . The computer readable medium according to claim 9 , further comprising instructions for:

applying at least one test to the plurality of calibration parameters; and

accepting the plurality of calibration parameters as an active set of calibration parameters if the plurality of calibration parameters are acceptable according to the at least one test.

11 . The computer readable medium according to claim 9 , wherein the first predetermined number of different readings comprises enough values to compute a constant bias along each axis of the magnetometer.

12 . The computer readable medium according to claim 11 , wherein at least 3 different readings are required to determine the first calibration parameter.

13 . The computer readable medium according to claim 9 , wherein the second predetermined number of different readings comprises enough values to compute constant bias, gain, and inter-axis misalignment parameters along each axis of the magnetometer.

14 . The computer readable medium according to claim 13 , wherein at least 9 different readings are required to determine the plurality of calibration parameters.

15 . The computer readable medium according to claim 9 , further comprising instructions for determining a radius of a sphere representing a magnetic field using the first predetermined number of different readings.

16 . The computer readable medium according to claim 9 , wherein the plurality of calibration parameters are determined using a least squares fitting algorithm.

17 . A mobile device comprising a processor coupled to a memory, and a magnetometer, the memory comprising computer executable instructions for calibrating the magnetometer, the computer executable instructions comprising instructions for:

obtaining a plurality of magnetometer sensor readings;

storing sensor readings from the plurality of obtained sensor readings that are different;

determining a first calibration parameter based on a first predetermined number of different readings; and

determining a plurality of calibration parameters based on a second predetermined number of different readings, wherein the plurality of calibration parameters includes the first calibration parameter.

18 . The mobile device according to claim 17 , further comprising instructions for:

applying at least one test to the plurality of calibration parameters; and

accepting the plurality of calibration parameters as an active set of calibration parameters if the plurality of calibration parameters are acceptable according to the at least one test.

19 . The mobile device according to claim 17 , wherein the first predetermined number of different readings comprises enough values to compute a constant bias along each axis of the magnetometer.

20 . The mobile device according to claim 19 , wherein at least 3 different readings are required to determine the first calibration parameter.

21 . The mobile device according to claim 17 , wherein the second predetermined number of different readings comprises enough values to compute constant bias, gain, and inter-axis misalignment parameters along each axis of the magnetometer.

22 . The mobile device according to claim 21 , wherein at least 9 different readings are required to determine the plurality of calibration parameters.

23 . The mobile device according to claim 17 , further comprising instructions for determining a radius of a sphere representing a magnetic field using the first predetermined number of different readings.

24 . The mobile device according to claim 17 , wherein the plurality of calibration parameters are determined using a least squares fitting algorithm.