Geomagnetic sensor calibration apparatus and method thereof

1. A geomagnetic sensor calibration apparatus comprising:

a geomagnetic sensor configured to measure at least one value of Earth's magnetic field; and

a processor configured to:

estimate first central points from the at least one measured value of the Earth's magnetic field by using a first linear function,

estimate second central points by using a second linear function and the estimated first central points,

determine whether calibration of the geomagnetic sensor is necessary based on the estimated first central points, and control the central point estimator to estimate second central points based on a result of the determination, and

calculate a mean value and a standard deviation value of distances between a plurality of sampling coordinates output from the geomagnetic sensor and the estimated first central points, and determine whether calibration of the geomagnetic sensor is necessary based on whether at least one of the calculated average value and standard deviation value exceeds a preset value.

2. The geomagnetic sensor calibration apparatus of claim 1 , wherein the at least one value of the Earth's magnetic field is expressed with coordinates in an X, Y, and Z coordinate space.

3. The geomagnetic sensor calibration apparatus of claim 1 , wherein the first linear function linearizes a function:

f=r i 2 −r 2 ,

wherein

r i =√{square root over (( X i −X 0 ) 2 +( Y i −Y 0 ) 2 +( Z i −Z 0 ) 2 )},

( X−X 0 ) 2 +( Y−Y 0 ) 2 +( Z−Z 0 ) 2 =r 2 ,

(X i , Y i , Z i ) are coordinate values sampled at an i-th number of the geomagnetic sensor,

(X 0 , Y 0 , Z 0 ) are the estimated first central points,

n is a predetermined integer, and

1≦i≦n.

4. The geomagnetic sensor calibration apparatus of claim 1 , wherein the second linear function linearizes a minimized function:

d i =r i −r 0 ,

wherein

r i =√{square root over (( X i −X 0 ) 2 +( Y i −Y 0 ) 2 +( Z i −Z 0 ) 2 )},

(X i , Y i , Z i ) are coordinate values sampled at an i-th number of the geomagnetic sensor,

(X 0 , Y 0 , Z 0 ) are the estimated first central points,

r 0 is a radius of a sphere having the estimated first central points,

n is a predetermined integer, and

1≦i≦n.

5. The geomagnetic sensor calibration apparatus of claim 1 , wherein the first linear function linearizes a minimized function:

d i =r i − r ,

wherein

r i =√{square root over (( X i −X 0 ) 2 +( Y i −Y 0 ) 2 +( Z i −Z 0 ) 2 )},

(X i , Y i , Z i ) are coordinate values sampled at an i-th number of the geomagnetic sensor,

(X 0 , Y 0 , Z 0 ) are the estimated first central points,

r is a constant value indicating a radius of a sphere having the estimated first central points,

n is a predetermined integer, and

1≦i≦n.

6. The geomagnectic sensor calibration apparatus of claim 1 , wherein the processor is further configured to calibrate central points by using a formula:

M

^

b

=

M

b

-

M

0

=

[

X

-

X

0

Y

-

Y

0

Z

-

Z

0

]

,

wherein M 0 =[X 0 , Y 0 , Z 0 ] T are coordinate values indicating central points estimated by the central point estimator, and

M b =[X, Y, Z] T are output values of the geomagnetic sensor.

7. The geomagnetic sensor calibration apparatus of claim 1 , wherein the geomagnetic sensor comprises:

a fluxgate of X, Y, and Z axes which are arranged orthogonally to each other;

a driving signal generator configured to provide driving signals to the fluxgate of X, Y, and Z axes;

a signal processor configured to, when the fluxgate of X, Y, and Z axes is driven by the driving signals and outputs electrical signals corresponding to surrounding magnetic field, convert the electrical signals to digital signals and output the digital signals; and

a geomagnetic sensor controller configured to perform normalization to map output values of the signal processor within a certain range by using offset values and preset scale values, and output normalized three-axis output values.

8. The geomagnetic sensor calibration apparatus of claim 1 , wherein the processor is further configured to calculate a pitch angle and a roll angle of the geomagnetic sensor calibration apparatus, and calculate azimuth by using the at least one measured value of the Earth's magnetic field, the pitch angle, and the roll angle.

9. The geomagnetic sensor calibration apparatus in claim 1 , wherein the geomagnetic sensor calibration apparatus comprises a remote controller.

10. A geomagnetic sensor calibration method comprising:

measuring at least one value of Earth's magnetic field;

estimating first central points from the at least one measured value of the Earth's magnetic field by using a first linear function;

estimating second central points by using a second linear function and the estimated first central points;

calculating an average value and a standard deviation value of distances between a plurality of sampled geomagnetic coordinates and the estimated first central points; and

determining whether calibration of the geomagnetic sensor is necessary based on whether at least one of the calculated average value and the standard deviation value exceeds a preset value.

11. The geomagnetic sensor calibration method of claim 10 , wherein the at least one measured value of the Earth's magnetic field is expressed with coordinates in an X, Y, and Z coordinate space.

12. The geomagnetic sensor calibration method of claim 10 , wherein the first linear function linearizes a function:

f=r i 2 −r 2 ,

wherein

r i =√{square root over (( X i −X 0 ) 2 +( Y i −Y 0 ) 2 +( Z i −Z 0 ) 2 )},

( X−X 0 ) 2 +( Y−Y 0 ) 2 +( Z−Z 0 ) 2 =r 2 ,

(X i , Y i , Z i ) are coordinate values sampled at an i-th number of the geomagnetic sensor,

(X 0 , Y 0 , Z 0 ) are the estimated first central points,

n is a predetermined integer, and

1≦i≦n.

13. The geomagnetic sensor calibration method of claim 10 , wherein the second linear function linearizes a minimized function:

d i =r i −r 0 ,

wherein

r i =√{square root over (( X i −X 0 ) 2 +( Y i −Y 0 ) 2 +( Z i −Z 0 ) 2 )},

(X i , Y i , Z i ) are coordinate values sampled at an i-th number of the geomagnetic sensor,

(X 0 , Y 0 , Z 0 ) are the estimated first central points,

r 0 is a radius of a sphere having the estimated first central points,

n is a predetermined integer, and

1≦i≦n.

14. The geomagnetic sensor calibration method of claim 10 , wherein the first linear function linearizes a minimized function:

d i =r i − r ,

wherein

r i =√{square root over (( X i −X 0 ) 2 +( Y i −Y 0 ) 2 +( Z i −Z 0 ) 2 )},

(X i , Y i , Z i ) are coordinate values sampled at an i-th number of the geomagnetic sensor,

(X 0 , Y 0 , Z 0 ) are the estimated first central points,

r is a constant value indicating a radius of a sphere having the estimated first central points,

n is a predetermined integer, and

1≦i≦n.

15. The geomagnetic sensor calibration method of claim 10 , further comprising:

calibrating central points by using a formula:

M

^

b

=

M

b

-

M

0

=

[

X

-

X

0

Y

-

Y

0

Z

-

Z

0

]

,

wherein M 0 =[X 0 , Y 0 , Z 0 ] T are coordinate values of the second central points estimated by the central point estimator, and

M b =[X, Y, Z] T are output values of the geomagnetic sensor.

16. The geomagnetic sensor calibration method of claim 10 , further comprising:

calculating a pitch angle and a roll angle of an electronic device; and

calculating azimuth by using the at least one measured value of the Earth's magnetic field, the pitch angle, and the roll angle.

17. A non-transitory computer readable medium which stores a program that is executed by a computer to perform the geomagnetic sensor calibration method of claim 10 .