Magnetometer normalization
Systems and methods for correcting received magnetometer coordinates of a measured magnetic bearing are disclosed. The measured magnetic bearing may be received from a calibrated magnetometer configured to measure the strength and direction of a magnetic field. In embodiments used to navigate a geographical area, the magnetic field comprises, at least in part, Earth's magnetic field. The magnetic field is subject to anomalies caused by metal structures in the vicinity of the magnetometer. The corrected magnetic bearing is based on a slope of the coordinates relative to a defined origin and a magnetic field constant, such as Earth's magnetic field constant. In some embodiments, the received magnetometer coordinates are filtered prior to correction. In some embodiments, a magnitude of the measured magnetic bearing relative to the defined origin is compared to an anomaly detection limit and a bearing validity indicator is output according to the result of the comparison.
1 . A method comprising:
receiving from a magnetometer coordinates of a measured magnetic bearing;
calculating a corrected magnetic bearing based on a slope of the coordinates relative to a defined origin and a magnetic field constant; and
outputting the corrected magnetic bearing.
2 . The method of claim 1 , wherein calculating the corrected magnetic bearing is according to the formulas
X
out
=
C
2
1
+
m
2
and
Y
out
=
m
*
C
2
1
+
m
2
where X out is a first magnitude of the corrected magnetic bearing along a first axis, Y out is a second magnitude of the corrected magnetic bearing along a second axis, C is the magnetic field constant, and m is the slope calculated according to the formula
m
=
Y
i
n
X
i
n
where X in is a first magnitude of the measured magnetic bearing along the first axis and Y in is a second magnitude of the measured magnetic bearing along the second axis.
3 . The method of claim 1 , further comprising filtering the received magnetometer coordinates of the measured magnetic bearing before calculating the corrected magnetic bearing.
4 . The method of claim 3 , wherein the filtering is performed using a Kalman filter.
5 . The method of claim 1 , further comprising:
comparing an anomaly detection limit to a magnitude of the measured magnetic bearing relative to the defined origin; and
outputting a bearing validity indicator according to the result of the comparison.
6 . The method of claim 5 , wherein comparing the anomaly detection limit to a magnitude of the measured magnetic bearing further comprises:
calculating a mean magnetic field magnitude; and
determining a difference between the magnitude of the measured magnetic bearing and the mean magnetic field magnitude.
7 . The method of claim 5 , further comprising:
determining whether to use the corrected magnetic bearing based on the bearing validity indicator; and
using a last known good bearing if the corrected magnetic bearing is not used.
8 . The method of claim 5 , further comprising:
determining whether to use the corrected magnetic bearing based on the bearing validity indicator; and
using another navigation aid if the corrected magnetic bearing is not used.
9 . The method of claim 1 , wherein the defined origin and the magnetic field constant are based on a calibration of the magnetometer.
10 . A system comprising:
a magnetic field circle application module configured to receive from a magnetometer a measured magnetic bearing, calculate a corrected magnetic bearing based on the measured magnetic bearing, a defined origin, and a magnetic field constant, and output the corrected magnetic bearing.
11 . The system of claim 10 , wherein the magnetic field circle application module is configured to calculate the corrected magnetic bearing according to the formulas
X
out
=
C
2
1
+
m
2
and
Y
out
=
m
*
C
2
1
+
m
2
where X out is a first magnitude of the corrected magnetic bearing along a first axis, Y out is a second magnitude of the corrected magnetic bearing along a second axis, C is the magnetic field constant, and m is the slope calculated according to the formula
m
=
Y
i
n
X
i
n
where X in is a first magnitude of the measured magnetic bearing along the first axis and Y in is a second magnitude of the measured magnetic bearing along the second axis.
12 . The system of claim 10 , further comprising a magnetic anomaly variable filter configured to filter the measured magnetic bearing and provide the filtered measured magnetic bearing to the magnetic field circle application module, instead of the measured magnetic bearing.
13 . The method of claim 12 , wherein the magnetic anomaly variable filter comprises a Kalman filter.
14 . The system of claim 10 , further comprising a magnetic field anomaly detector configured to compare an anomaly detection limit to a magnitude of the measured magnetic bearing relative to the defined origin and output a bearing validity indicator according to the result of the comparison.
15 . The system of claim 14 , wherein magnetic field anomaly detector is further configured to calculate a mean magnetic field magnitude and determine a difference between the magnitude of the measured magnetic bearing and the mean magnetic field magnitude.
16 . The system of claim 10 , wherein the defined origin and the magnetic field constant are based on a calibration of the magnetometer.
17 . A computer readable storage medium having embodied thereon a program, the program being executable by a processor for performing a method for correcting a magnetic bearing, the method comprising:
receiving from a magnetometer coordinates of a measured magnetic bearing;
calculating a corrected magnetic bearing based on a slope of the coordinates relative to a defined origin and a magnetic field constant; and
outputting the corrected magnetic bearing.
18 . The computer readable medium of claim 17 , wherein calculating the corrected magnetic bearing is according to the formulas
X
out
=
C
2
1
+
m
2
and
Y
out
=
m
*
C
2
1
+
m
2
where X out is a first magnitude of the corrected magnetic bearing along a first axis, Y out is a second magnitude of the corrected magnetic bearing along a second axis, C is the magnetic field constant, and m is the slope calculated according to the formula
m
=
Y
i
n
X
i
n
where X in is a first magnitude of the measured magnetic bearing along the first axis and Y in is a second magnitude of the measured magnetic bearing along the second axis.
19 . The computer readable medium of claim 17 , wherein the method further comprises filtering the received magnetometer coordinates of the measured magnetic bearing before calculating the corrected magnetic bearing.
20 . The computer readable medium of claim 17 , wherein the method further comprises:
comparing an anomaly detection limit to a magnitude of the measured magnetic bearing relative to the defined origin; and
outputting a bearing validity indicator according to the result of the comparison.