Magnetometer accuracy and use

• US 7,891,103 B2
• Filed: 06/05/2009
• Issued: 02/22/2011
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Piemonte, Patrick, Mayor, Robert, Huang, Ronald Keryuan, Patel, Parin
• Primary Examiner(s): Fulton; Christopher W
• Application Number:
  US12/479,717
• Publication Number:
  US 20100307016A1
• Time in Patent Office: 627 Days
• Field of Search: 333/56
• US Class Current: 33/356
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01R 33/10 Plotting field distribution ; Measuring field distribution
• CPC Class Codes: G01V 3/087 the earth magnetic field being modified by the objects or geological structures
• CPC Class Codes: G08B 7/06 using electric transmission , e.g. involving audible and visible signalling through the use of sound and light sources

Abstract

A parameter related to the Earth'"'"'s magnetic field can be used to determine accuracy of a magnetometer of a mobile device. In one aspect, a first instance of a parameter related to Earth'"'"'s magnetic field is determined using data generated by the magnetometer. The magnetometer data can be based in part on a position of the mobile device with respect to the Earth. A second instance of the parameter can be determined using data generated by a model of Earth'"'"'s magnetic field. The model data can also be based in part on the position of the mobile device with respect to the Earth. The first instance of the parameter can be compared with the second instance of the parameter. An accuracy metric for the magnetometer can be determined based on a result of the comparison. An indication of the accuracy metric can be presented by the mobile device.

Claims

1. A method performed by a processor of a mobile device having a magnetometer, the method comprising:

determining a first instance of a parameter related to Earth'"'"'s magnetic field using first data generated by the magnetometer, the first data based at least in part on a position of the mobile device with respect to the Earth;

determining a second instance of the parameter using second data generated by a model of Earth'"'"'s magnetic field, the second data based at least in part on the position of the mobile device with respect to the Earth;

comparing the first instance of the parameter with the second instance of the parameter;

determining an accuracy metric for the magnetometer based on results of the comparison; and

presenting an indication of the accuracy metric on the mobile device.

2. The method of claim 1, where the first instance of a parameter is an angle between Earth'"'"'s magnetic vector and Earth'"'"'s gravitational acceleration vector defined in a Cartesian coordinate frame, and the second instance of the parameter is the angle provided by the model of Earth'"'"'s magnetic field.

3. The method of claim 1, where comparing the first instance of the parameter with the second instance of the parameter includes computing a statistical value based on a difference between the first and second instances of the parameter.

4. The method of claim 1, where presenting an indication of the accuracy metric on the mobile device includes displaying a visual representation of the accuracy metric on a display of the mobile device.

5. The method of claim 4, where the visual representation includes a portion of a map that is marked to indicate a heading error associated with an orientation of the mobile device relative to the map.

6. An apparatus, comprising:

a magnetometer; and

a processor coupled to the magnetometer, the processor configured for;

determining a first instance of a parameter related to Earth'"'"'s magnetic field using first data generated by the magnetometer, the first data based at least in part on a position of the mobile device with respect to the Earth;

determining a second instance of the parameter using second data generated by a model of Earth'"'"'s magnetic field, the second data based at least in part on the position of the mobile device with respect to the Earth;

comparing the first instance of the parameter with the second instance of the parameter;

determining an accuracy metric for the magnetometer based on results of the comparison; and

presenting an indication of the accuracy metric on the mobile device.

7. The apparatus of claim 6, where the first instance of a parameter is an angle between Earth'"'"'s magnetic vector and Earth'"'"'s gravitational acceleration vector defined in a Cartesian coordinate frame, and the second instance of the parameter is the angle provided by the model of Earth'"'"'s magnetic field.

8. The apparatus of claim 6, where comparing the first instance of the parameter with the second instance of the parameter includes computing a statistical value based on a difference between the first and second instances of the parameter.

9. The apparatus of claim 6, where presenting an indication of the accuracy metric on the mobile device includes displaying a visual representation of the accuracy metric on a display of the mobile device.

10. The apparatus of claim 9, where the visual representation includes a portion of a map that is marked to indicate a heading error associated with an orientation of the mobile device relative to the map.

11. The apparatus of claim of claim 10, where the display is touch sensitive.

12. A computer-readable, non-transitory medium having instructions stored thereon, which, when executed by a processor, causes at least one processor to perform operations comprising:

determining a first instance of a parameter related to Earth'"'"'s magnetic field using first data generated by the magnetometer, the first data based at least in part on a position of the mobile device with respect to the Earth;

determining a second instance of the parameter using second data generated by a model of Earth'"'"'s magnetic field, the second data based at least in part on the position of the mobile device with respect to the Earth;

comparing the first instance of the parameter with the second instance of the parameter;

determining an accuracy metric for the magnetometer based on results of the comparison; and

presenting an indication of the accuracy metric on the mobile device.

13. The computer-readable medium of claim 12, where the first instance of a parameter is an angle between Earth'"'"'s magnetic vector and Earth'"'"'s gravitational acceleration vector defined in a Cartesian coordinate frame, and the second instance of the parameter is the angle provided by the model of Earth'"'"'s magnetic field.

14. The computer-readable medium of claim 12, where comparing the first instance of the parameter with the second instance of the parameter includes computing a statistical value based on a difference between the first and second instances of the parameter.

15. The computer-readable medium of claim 12, where presenting an indication of the accuracy metric on the mobile device includes displaying a visual representation of the accuracy metric on a display of the mobile device.

16. The computer-readable medium of claim 15, where the visual representation includes a portion of a map that is marked to indicate a heading error associated with an orientation of the mobile device relative to the map.

17. A method performed by a processor of a mobile device having a magnetometer, the method comprising:

determining an accuracy metric based on magnetometer measurements output by the magnetometer during a calibration or recalibration procedure; and

presenting an indication of the accuracy metric on the mobile device.

18. The method of claim 17, where presenting an indication of the accuracy metric on the mobile device includes displaying a visual representation of the accuracy metric on a display of the mobile device.

19. The method of claim 18, where the visual representation includes a portion of a map that is marked to indicate a heading error associated with an orientation of the mobile device relative to the map.

20. The method of claim 18, where the visual representation indicates heading error.

21. The method of claim 18, where presenting an indication of the accuracy metric on the mobile device includes presenting an audio output to a user of the mobile device.

22. An apparatus, comprising:

a magnetometer; and

a processor coupled to the magnetometer, the processor configured for;

determining an accuracy metric based on magnetometer measurements output by the magnetometer during a calibration or recalibration procedure; and

presenting an indication of the accuracy metric on the mobile device.

23. The apparatus of claim 22, where presenting an indication of the accuracy metric on the mobile device includes displaying a visual representation of the accuracy metric on a display of the mobile device.

24. The apparatus of claim 23, where the visual representation includes a portion of a map that is marked to indicate a heading error associated with an orientation of the mobile device relative to the map.

25. The apparatus of claim 23, where the visual representation indicates heading error.

26. The apparatus of claim 22, where presenting an indication of the accuracy metric on the mobile device includes presenting an audio output to a user of the mobile device.