Method and apparatus for calculating azimuth

• US 10,267,649 B2
• Filed: 04/02/2014
• Issued: 04/23/2019
• Est. Priority Date: 07/24/2013
• Status: Active Grant

• Current Assignee: Magnachip Semiconductor Limited (Magnachip Semiconductor)
• Original Assignee: Magnachip Semiconductor Limited (Magnachip Semiconductor)
• Inventors: Kim, Dong Ho, Cho, Ki Seok
• Primary Examiner(s): Satanovsky, Alexander
• Assistant Examiner(s): Fairbanks, Brent A.
• Application Number:
  US14/243,643
• Publication Number:
  US 20150032409A1
• Time in Patent Office: 1,847 Days
• Field of Search: None
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A method and an apparatus for calculating azimuth, and a method and an apparatus for determining an offset from geomagnetic field are provided. An apparatus for calculating azimuth includes a magnetic sensor configured to sense magnetic field, a data selecting unit configured to select offset data items, an offset calculating unit configured to calculate an offset by a geometrical method that uses the selected offset data items, and an azimuth calculating unit configured to calculate an azimuth by using the calculated offset.

Claims

1. An apparatus comprising:

a magnetic sensor configured to sense a magnetic field and convert the sensed magnetic field into a voltage;

an amplifier configured to amplify the voltage;

an analog-to-digital converter configured to convert the amplified voltage into voltage data; and

a processor configured to execute instructions stored in a memory, thereby configuring the processor to;

separate the voltage data into 3-axis magnetic field components in X, Y and Z axes to generate separated voltage data;

remove noise components of the separated voltage data by creating a median value of the separated voltage data and filtering the separated voltage data by selecting midmost voltage data;

apply a previously calculated offset to the filtered separated voltage data;

determine, based on the application of the previously calculated offset, whether the filtered separated voltage data correspond to a geomagnetic field;

selectively, based on a result of the determining of whether the filtered separated voltage data correspond to the geomagnetic field,

select offset data items from the filtered separated voltage data,

subtract a difference between the filtered separated voltage data and previously measured voltage data from a previous offset reference point,

set a resultant value as a new offset reference point, in response to the filtered separated voltage data being determined not to correspond to the geomagnetic field and the previously measured voltage data being determined to correspond to the geomagnetic field, and

calculate an offset by a geometrical method that uses the selected offset data items and the new offset reference point; and

determine a location or directional information of the apparatus based on the voltage data for the sensed magnetic field and selectively one of the calculated offset and the previously calculated offset, with increased location or directional determination speed and/or accuracy with respect to a presence of an abnormal magnetic field.

2. The apparatus according to claim 1, wherein the processor is further configured, through the execution of the instructions, to remove an instantaneous noise from measurements of the magnetic field.

3. The apparatus according to claim 1, wherein the processor is further configured, through the execution of the instructions, to select at least three data items as the selected offset data items, including two distant X or Y axis voltage data items and an X or Y voltage data item between the two distant voltage data items.

4. The apparatus according to claim 3, wherein the processor is further configured, through the execution of the instructions, to use two values, which are a value having the greatest difference in distance between data items in a measured data group and a value having the second greatest difference, as main-calculation data items, and

wherein, when arranged in order of X values, a data item between the two values is used as sub-calculation data.

5. The apparatus according to claim 4, wherein the processor is further configured, through the execution of the instructions, to set one point that is farther from the sub-calculation data, among intersecting points of two circles having the two main-calculation data items as centers and each having a radius r, as the calculated offset.

6. The apparatus according to claim 1,

wherein the determining of the location or directional information of the apparatus includes, based on a result of the determining of whether the filtered separated voltage data correspond to the geomagnetic field,

determining the location or directional information based on the previously calculated offset, without performing the selecting of the offset data items, the subtracting of the difference, the setting of the resultant value, and the calculating of the offset, in response to determining that the magnetic field is the geomagnetic field, and

determining the location or directional information based on the calculated offset in response to determining that the magnetic field is not the geomagnetic field.

7. The apparatus according to claim 1, wherein the filtered separated voltage data that is presently measured is represented as C₁(X_c, Y_c) and the filtered separated voltage data which is previously measured is represented as P₁(X_p, Y_p), and in response to a determination that the P₁ is the geomagnetic field and the C₁ is not the geomagnetic field, the processor is controlled to subtracts a difference between the C₁(X_c, Y_c) and the P₁(X_p, Y_p) from the previously calculated offset and set a resultant value as the new offset reference point.

8. The apparatus according to claim 1, wherein the determination of whether the filtered separated voltage data correspond to the geomagnetic field is based on consideration of a dip angle with respect to the Z axis in the XY plane and magnitudes of the magnetic field in the X, Y, and Z axes.

9. A processor-implemented method of determining a location or directional information of an apparatus comprising a magnetic sensor, an amplifier, an analog-to-digital converter, and a processor, the method comprising:

sensing, using the magnetic sensor, a magnetic field and converting the sensed magnetic field into a voltage;

amplifying, using the amplifier, the voltage;

converting, using the analog-to-digital converter, the amplified voltage into voltage data;

controlling, through execution by a processor of instructions stored in a memory, the processor to;

separate the voltage data into 3-axis magnetic field components in X, Y and Z axes to generate separated voltage data;

remove noise components of the separated voltage data by creating a median value of the separated voltage data and filtering the separated voltage data by selecting midmost voltage data;

apply a previously calculated offset to the filtered separated voltage data;

determine, based on the application of the previously calculated offset, whether the filtered separated voltage data correspond to a geomagnetic field;

selectively, based on a result of the determining of whether the filtered separated voltage data correspond to the geomagnetic field,

select offset data from the filtered separated voltage data which do not correspond to the geomagnetic field,

subtract a difference between the filtered separated voltage data and previously measured voltage data from the previously calculated offset and setting a resultant value as a new offset reference point, in response to the previously measured voltage data being determined to correspond to the geomagnetic field, and

calculate an offset by using the selected offset data and the new offset reference point; and

determine a location or directional information of the apparatus based on the voltage data for the sensed magnetic field and selectively one of the calculated offset, another calculated offset, and the previously calculated offset, with increased location or directional determination speed and/or accuracy with respect to a presence of an abnormal magnetic field,

wherein, when the filtered separated voltage data does not correspond to the geomagnetic field, the location or directional information of the apparatus is determined based on the voltage data for the sensed magnetic field and the calculated offset in response to a determination that the calculated offset is within a set range of a reference point, and determined based on the voltage data for the sensed magnetic field and the other calculated offset, calculated by a geometrical method that uses the previously calculated offset, in response to a determination that the calculated offset is outside the set range of the reference point.

10. The method according to claim 9, wherein, in the selecting of the offset data, two values, which are a value having the greatest difference in distance between data items in a measured data group and a value having the second greatest difference, are used as main-calculation data items, and

wherein, when arranged in order of X values, a data item between the two values is used as sub-calculation data.

11. The method according to claim 10, wherein in the selecting of the offset data, data items that are sequentially input are sorted in order of magnitude, and a middle data item of the arranged data items is selected to remove a noise.

12. The method according to claim 10, wherein the selected offset data items comprise at least three data items.

13. The method according to claim 12, wherein the selecting of the three data items comprises:

storing a number of 2-axis or 3-axis data items;

calculating X_diff and Y_diff by performing an operation of the following equations by using the stored data items;

selecting two of the stored data items having the largest value and the second largest value from among the X_diff and the Y_diff and selecting the two of the stored data items as main-calculation data items C and D,

wherein if the X_diff is selected when the X_diff is larger than the Y_diff, the selected two of the stored data items are Xmax and Xmin, and

wherein if the Y_diff is selected when the X_diff is smaller than the Y_diff, the selected two of the stored data items are Ymax and Ymin;

in response to the X_diff being selected, selecting data having an X value closest to X_avg, and in response to the Y_diff being selected, selecting data having a Y value closest to Y_avg; and

selecting the data selected as the data having an X value closest to X_avg or the data having a Y value closest to Y_avg as sub-calculation data E, in accordance with equations;

X_diff=X_max−

X_min,

Y_diff=Y_max−

Y_min,

X_avg=(X_max+X_min)/2,

Y_avg=(Y_max+Y_min)/2,

wherein X_max, X_min, Y_max, and Y_min are output values of the median filter, and X_avg and Y_avg are average values.

14. The method according to claim 13, wherein the calculating of the offset, by using the selected three data items, comprises:

forming a circle having the main-calculation data C as a center and a radius r and a circle having the main-calculation data D as a center and the radius r, where one point of intersecting points a1 and a2 of the circles as correspond to a changed offset reference point B, such that with coordinates of the main-calculation data C being X₁ and Y₁, coordinates of the main-calculation data D being X₂ and Y₂, coordinates of the changed offset reference point B being ^OX and ^OY, and coordinates of the sub-calculation data E being X₃ and Y₃, the coordinates of the changed offset reference point B are calculated according to the following equations;

(X₁−

^OX)²+(Y₁−

^OY)²=r²; and

(X₂−

^OX)²+(Y₂−

^OY)²=r²,

wherein a1 and a2 are roots of the equations, and among the roots, a root farther from the sub-calculation data E is set as the changed offset reference point B, and set as the calculated offset.

15. The method according to claim 10,

wherein the filtered separated voltage data that is presently measured is represented as C₁(X_c, Y_c) and the filtered separated voltage data which is previously measured is represented as P₁(X_p, Y_p), and in response to a determination that the P₁ is the geomagnetic field and the C₁ is not the geomagnetic field, the processor is controlled to subtracts a difference between the C₁(X_c, Y_c) and the P₁(X_p, Y_p) from the previously calculated offset and sets a resultant value as the new offset reference point.

16. The method according to claim 10, wherein the method further comprising controlling the magnetic sensor to sense the magnetic field for obtaining the voltage data.

17. A processor-implemented method of determining a location or directional information of an apparatus comprising a magnetic sensor, an amplifier, an analog-to-digital converter, and a processor, the method comprising:

sensing and measuring, using the magnetic sensor, a magnetic field and converting the sensed and measured magnetic field into a voltage;

amplifying, using the amplifier, the voltage;

converting, using the analog-to-digital converter, the amplified voltage into voltage data; and

controlling, through execution by a processor of instructions stored in a memory, the processor to;

separate the voltage data into 3-axis magnetic field components in X, Y and Z axes to generate separated voltage data;

remove noise components of the separated voltage data by creating a median value of the separated voltage data, and filtering the separated voltage data by selecting midmost voltage data;

apply a previously calculated offset to the filtered separated voltage data;

determine, based on the application of the previously calculated offset, whether the filtered separated voltage data correspond to a geomagnetic field;

selectively, based on a result of the determining of whether the filtered separated voltage data correspond to the geomagnetic field,

select offset data items for calculating an offset from the filtered separated voltage data,

select a median value or a value in a midmost position of data in a collected data group, arranged in order of magnitude to form a measured data group,

subtract a difference between the filtered separated voltage data and previously measured voltage data from the previously calculated offset and setting a resultant value as a new offset reference point, in response to the filtered separated voltage data being determined not to correspond to the geomagnetic field and the previously measured voltage data being determined to correspond to the geomagnetic field, and

calculate the offset by applying a geometric method to the selected offset data item and the new offset reference point; and

determine a location or directional information of the apparatus based on the voltage data for the sensed magnetic field and selectively one of the calculated offset and the previously calculated offset, with increased location or directional determination speed and/or accuracy with respect to a presence of an abnormal magnetic field.

18. The method according to claim 17, wherein the controlling of the processor further comprises controlling the processor to:

separate the voltage data into components along two or more axes to obtain a collected data group.

19. The method according to claim 17, wherein the selecting of the median value or the value in the midmost position of the data in the collected data group comprises selecting two values having the greatest difference and the second greatest difference in distance between data items in a measured data group, and further selecting the value between the two values.

20. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to perform the method of claim 17.