Accuracy indications for an electronic compass in a portable device

• US 7,921,572 B2
• Filed: 06/05/2009
• Issued: 04/12/2011
• Est. Priority Date: 06/05/2009
• Status: Expired due to Fees

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Piemonte, Patrick S., Huang, Ronald K., Mayor, Robert, Patel, Parin
• Primary Examiner(s): Fulton; Christopher W
• Application Number:
  US12/479,196
• Publication Number:
  US 20100307015A1
• Time in Patent Office: 676 Days
• Field of Search: 333/56
• US Class Current: 33/356
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

Multiple instances of a geomagnetic field are calculated. Multiple instances of an average magnitude of a subset of the instances of the geomagnetic field are also calculated. When the average magnitude changes by more than a first predetermined threshold, the user is informed that compass accuracy has degraded. Other embodiments are also described and claimed.

Claims

1. A machine-implemented method for providing a user with accuracy indications for a compass, comprising:

calculating a first plurality of instances of a geomagnetic field;

calculating a second, different plurality of instances of the geomagnetic field;

calculating an average magnitude of the first plurality of instances of the geomagnetic field;

calculating an average magnitude of the second plurality of instances of the geomagnetic field;

detecting whether the average magnitudes of the first plurality of instances and the second plurality of instances differ by more than a first predetermined threshold; and

informing the user that compass accuracy has degraded, in response to having detected that the average magnitudes differ by more than the first predetermined threshold.

2. The method of claim 1 wherein calculating an average magnitude of the first plurality of instances, calculating an average magnitude of the second plurality of instances, and detecting whether the average magnitudes differ comprises:

maintaining a moving average of the geomagnetic field and detecting whether the moving average changes by more than the first predetermined threshold.

3. The method of claim 2 further comprising:

signaling a recalibration of the compass to recalculate an estimated interference field, in response to having detected that the moving average has changed by more than a second predetermined threshold.

4. The method of claim 1 further comprising:

estimating an error bound for a computed direction given by the compass, wherein said informing the user comprises informing the user of the estimated error bound.

5. The method of claim 1 further comprising:

signaling a recalibration of the compass to recalculate an estimated interference field using a different type of compass calibration process selected from the group consisting of a 2D process and a 3D process, in response to having detected that the moving average has changed by more than a second predetermined threshold.

6. A portable device comprising:

a portable device housing having integrated therein

a magnetic sensor;

a compass calibrator to compute a plurality of instances of a geomagnetic field based on an observed magnetic field and an estimated magnetic interference field;

a compass accuracy indicator module to calculate a plurality of instances of an average magnitude of a subset of the plurality of instances of the geomagnetic field, and to detect whether the average magnitude changes by more than a predetermined threshold; and

a user interface module coupled to drive one of a speaker and a display screen of the portable device, wherein the compass accuracy indicator module is to use the user interface module to inform a user of the portable device that compass accuracy has degraded in response to having detected that the average magnitude has changed by more than the predetermined threshold.

7. The portable device of claim 6 compass accuracy indicator module is to calculate a plurality of instances of an average magnitude and detect whether the average magnitude changes, in order to maintain a moving average of the geomagnetic field and detect whether the moving average changes by more than the predetermined threshold.

8. The portable device of claim 6 wherein the compass accuracy indicator module is to estimate an error bound for a computed compass direction output, and uses the user interface module to inform the user of the estimated error bound.

9. The portable device of claim 6 wherein the compass accuracy indicator module is to signal compass recalibration to recalculate the estimated interference field, in response to having detected that the average magnitude has changed by more than a second predetermined threshold.

10. An article of manufacture comprising:

a non-transitory machine-readable medium having stored therein instructions that program a processor, of a portable device having an integrated magnetic sensor, to compute a plurality of instances of a geomagnetic field using the magnetic sensor, calculate a plurality of instances of an average magnitude of a subset of the plurality of instances of the geomagnetic field, detect whether the average magnitude changes by more than a predetermined threshold, and signal a user interface module of the portable device that compass accuracy has degraded in response to having detected that the average magnitude has changed by more than the predetermined threshold.

11. The article of manufacture of claim 10 wherein the non-transitory machine-readable medium has stored therein further instructions that program the processor to calculate a plurality of instances of an average magnitude and detect whether the average magnitude changes, in order to maintain a moving average of the geomagnetic field and detect whether the moving average changes by more than the predetermined threshold.

12. The article of manufacture of claim 10 wherein the non-transitory machine-readable medium has stored therein further instructions that program the processor to estimate an error bound for a computed compass direction output, and signal the user interface module to inform the user of the estimated error bound.

13. The article of manufacture of claim 10 wherein the non-transitory machine-readable medium has stored therein further instructions that program the processor to signal compass recalibration to recalculate an estimated interference field, in response to having detected that the average magnitude has changed by more than a second predetermined threshold.

14. A machine-implemented method for providing a user with accuracy indications for a compass, comprising:

calculating a first set of two or more instances of a geomagnetic field;

calculating a second, different set of two or more instances of the geomagnetic field;

calculating an average magnitude of the first set of two or more instances of the geomagnetic field;

calculating an average magnitude of the second set of two or more instances of the geomagnetic field;

detecting whether a difference between the average magnitudes of the first set and second set exceeds a first predetermined threshold; and

informing the user that compass accuracy has degraded, in response to having detected that the difference between the average magnitudes has exceeded the first predetermined threshold.

15. The method of claim 14 wherein calculating an average magnitude of the first set and calculating an average magnitude of the second set comprises:

maintaining a moving average of the geomagnetic field.

16. The method of claim 14 further comprising:

estimating an error bound for a computed direction given by the compass, wherein informing the user comprises informing the user of the estimated error bound.

17. The method of claim 14 further comprising:

signaling a recalibration of the compass to recalculate an estimated interference field, in response to having detected that the difference between the average magnitudes has exceeded a second predetermined threshold.

18. A machine-implemented method for providing a user with accuracy indications for a compass, comprising:

calculating a plurality of instances of a geomagnetic field;

calculating a magnitude for each instance of the geomagnetic field;

maintaining a moving average of the magnitudes of the plurality of instances of the geomagnetic field;

detecting whether the moving average changes by more than a first predetermined threshold; and

informing the user that compass accuracy has degraded, in response to having detected that the moving average has changed by more than the first predetermined threshold.

19. The method of claim 18 further comprising:

estimating an error bound for a computed direction given by the compass, wherein informing the user comprises informing the user of the estimated error bound.

20. The method of claim 18 further comprising:

signaling a recalibration of the compass to recalculate an estimated interference field, in response to having detected that the moving average has changed by more than a second predetermined threshold.