Vehicle compass system with continuous automatic calibration
View Patent ↗The compass system of the present invention utilizes an improved calibration routine in which a processing circuit of the compass recalibrates the compass each time three data points are obtained from a magnetic field sensor that meet predetermined criteria. One such criterion is that the three data points define corners of a triangle that is substantially non-obtuse. When three data points have been obtained that define a triangle meeting this criterion, the processing circuit calculates a center point for a circle upon which all three data points lie by solving the equation x 2 +y 2 +Ax+By+C=0 for A, B, and C, using the coordinate values (x,y) for the three data points and defining the center point as (−A/2, −B/2).
1. A method for calibrating an electronic vehicular compass, comprising:
receiving electronic data from a sensor circuit in the vehicle, the sensor circuit configured to measure an effect of the earth's magnetic field;
calculating a first smoothed data point using data points received from the sensor circuit;
calculating a second smoothed data point using the data points received from the sensor circuit;
calculating a third smoothed data point using the data points received from the sensor circuit;
calculating a center point based on at least the first smoothed data point, second smoothed data point and third smoothed data point;
calculating a fourth smoothed data point using data received from the sensor circuit;
calculating the distance from the fourth smoothed data point to the center point; and
not processing the fourth smoothed data point if a distance between the fourth smoothed data point and the center point is outside of a predetermined range.
2. The method of claim 1 , wherein calculating the fourth smoothed data point from the sensor circuit is performed only when the vehicle is moving faster than a predetermined limit.
3. The method of claim 2 , wherein the predetermined limit is 10 miles per hour.
4. The method of claim 1 , wherein the predetermined range is a function of a radius of a circular shape based on at least the first smoothed data point, second smoothed data point and third smoothed data point.
5. The method of claim 4 , wherein the predetermined range requires that the distance between the fourth smoothed data point and the center point be greater than half of the radius.
6. The method of claim 5 , wherein the predetermined range requires that the distance between the fourth smoothed data point and the center point be less than 1.5 times the radius.
7. The method of claim 4 , wherein the predetermined range requires that the distance between the fourth smoothed data point and the center point be less than 1.5 times the radius.
8. The method of claim 1 , further comprising:
not processing a data point received prior to receiving the fourth smoothed data point if the distance between the fourth smoothed data point and the center point is outside of the predetermined range.
9. The method of claim 1 , further comprising displaying a heading based on the electronic data received from the sensor circuit.
10. A self-calibrating electronic vehicular compass, comprising:
a sensor circuit configured to measure an effect of the earth's magnetic field and communicate measurements as data points;
a processing circuit configured to:
(i) receive measured data points from the sensor circuit;
(ii) provide a first smoothed data point using the measured data points;
(iii) provide a second smoothed data point using the measured data points;
(iv) provide a third smoothed data point using the measured data points;
(v) provide a center point defined by the coordinates of the first smoothed data point, second smoothed data point and third smoothed data point;
(vi) provide the distance from a fourth data point and the center point; and
(vii) not process the fourth data point if a distance between the fourth data point and the center point is outside of a predetermined range.
11. The compass of claim 10 , wherein the processor circuit is configured to use the data point only when the vehicle is moving faster than a predetermined limit.
12. The compass of claim 11 , wherein the predetermined limit is 10 miles per hour.
13. The compass of claim 10 , wherein the predetermined range is a function of a radius of a circular shape.
14. The compass of claim 13 , wherein the predetermined range requires that the distance between the data point and the center point be greater than half of the radius.
15. The compass of claim 14 , wherein the predetermined range requires that the distance between the data point and the center point be less than 1.5 times the radius.
16. The compass of claim 10 , wherein the predetermined range requires that the distance between the data point and the center point be less than 1.5 times the radius.
17. The compass of claim 10 , wherein the processor circuit is further configured to not process a data point received prior to receiving the data point if the distance between the data point and the center point is outside of the predetermined range.
18. The compass of claim 10 , wherein the processor circuit is further configured to display a heading based on the measured data points received from the sensor circuit.
19. A processing circuit for a vehicle compass configured to:
receive measured data points from a sensor circuit;
provide a first smoothed data point;
provide a second smoothed data point;
provide a third smoothed data point;
provide a center point defined by the coordinates of the first smoothed data point, second smoothed data point and third smoothed data point;
provide a distance from a fourth data point and the center point; and
not use the fourth data point if a distance between the data point and the center point is outside of a predetermined range.
20. The processing circuit of claim 19 , wherein the processing circuit is configured to use the fourth data point only when the vehicle is moving faster than a predetermined limit.
21. The processing circuit of claim 19 , wherein the predetermined range is a function of a radius of a circular shape.
22. The processing circuit of claim 21 , wherein the predetermined range requires that the distance between the fourth data point and the center point be greater than half of the radius.
23. The processing circuit of claim 22 , wherein the predetermined range requires that the distance between the fourth data point and the center point be less than 1.5 times the radius.
24. The processing circuit of claim 19 , wherein the predetermined range requires that the distance between the fourth data point and the center point be less than 1.5 times the radius.
25. The processing circuit of claim 19 , wherein the processor circuit is further configured to not use a fourth data point received prior to receiving the data point if the distance between the fourth data point and the center point is outside of the predetermined range.