Calibration program and electronic compass

1. A calibration method that is executed by a computer for finding a reference point for the output of a magnetic sensor, comprising:

obtaining at least four outputs from the magnetic sensor wherein at least one output contains an error;

forming at least two triangles from said at least four outputs of the magnetic sensor in a three-dimensional space, the at least two triangles including a first triangle and a second triangle;

finding a first circle circumscribing the first triangle and a second circle circumscribing the second triangle, the first circle and the second circle each corresponding to a cut section of a virtual sphere;

obtaining a first normal vector and a second normal vector passing through a center of the first circle and a center of the second circle, respectively;

finding the reference point as an intersection of the first and second normal vectors, the reference point being the center of the virtual sphere; and

calibrating the magnetic sensor using the reference point,

wherein said finding the reference point includes:

acquiring a plurality of sets of said at least four outputs, wherein each set defines the corresponding virtual sphere; and

finding an average of a group of centers, each center being found on the basis of the corresponding set of said at least four outputs.

2. The calibration method according to claim 1 , wherein said at least four outputs are obtained so as to satisfy following two conditions:

(a) each distance between the point of one output and the point of another output is not smaller than a predetermined distance value; and

(b) each planed angle formed by said at least two triangles does not exceed a predetermined angle tolerance (Δθ), the center of which is 90°.

3. An electronic compass comprising:

a compass module that is provided with a magnetic sensor; and

a controlling section provided with a calibration program and performs the calibration method according to claim 2 , so as to find the reference point for the output of the magnetic sensor, the controlling section being further provided with a compass direction calculation program and finding a compass direction with the use of the output of the magnetic sensor.

4. The calibration method according to claim 1 , wherein said at least four outputs are obtained so as to satisfy following three conditions:

(a) each distance between the point of one output and the point of another output is not smaller than a predetermined distance value;

(b) the distance between the found center of the virtual sphere and each of said at least four outputs is not larger than a predetermined distance value; and

(c) each planed angle that is formed by said at least two triangles does not exceed a predetermined angle tolerance (Δθ), the center of which is 90°.

5. An electronic compass comprising:

a compass module that is provided with a magnetic sensor; and

a controlling section provided with a calibration program and performs the calibration method according to claim 1 , so as to find the reference point for the output of the magnetic sensor, the controlling section being further provided with a compass direction calculation program and finding a compass direction with the use of the output of the magnetic sensor.

6. The electronic compass according to claim 5 , wherein the controlling section is further provided with a plurality of buffers each of which can store said at least four outputs; and the controlling section judges whether it is possible to store the output of the magnetic sensor into the plurality of buffers or not on the basis of predetermined judgment conditions.

7. The electronic compass according to claim 5 , wherein the controlling section automatically runs the calibration program in response to the occurrence of a change in the ambient conditions of the magnetic sensor.

8. A calibration method that is executed by a computer for finding a reference point for the output of a magnetic sensor, comprising:

obtaining at least four outputs from the magnetic sensor wherein at least one output contains an error;

forming at least two triangles from said at least four outputs of the magnetic sensor in a three-dimensional space;

finding, for each of said at least two triangles, a circle circumscribed about the triangle, each circle corresponding to a cut section of a virtual sphere; and

finding an intersection of normal vectors each of which passes through a center of the corresponding circumscribed circle so as to find the reference point, the reference point being the center of the virtual sphere; and

calibrating the magnetic sensor using the reference point,

wherein said finding the reference point includes:

acquiring a plurality of sets of said at least four outputs, wherein each set defines the corresponding virtual sphere; and

finding an average of a group of centers, each center being found on the basis of the corresponding set of said at least four outputs, and

wherein said at least four outputs are obtained so as to satisfy following two conditions: a first condition is that each distance between a point of one output and a point of another output is not smaller than a predetermined distance value; and a second condition is that a planed angle or each planed angle that is formed by said at least two triangles does not exceed a predetermined angle tolerance (Δθ), the center of which is 90°.

9. An electronic compass comprising:

a compass module that is provided with a magnetic sensor; and

a controlling section provided with a calibration program and performs the calibration method according to claim 8 , so as to find the reference point for the output of the magnetic sensor, the controlling section being further provided with a compass direction calculation program and finding a compass direction with the use of the output of the magnetic sensor.