Virtual sensor and compass calibration

1. An unmanned aerial vehicle comprising:

one or more magnetometers, configured to detect a magnetic field and to output magnetometer data corresponding to a magnitude of the detected magnetic field;

a position sensor, configured to detect a position of the unmanned aerial vehicle relative to one or more reference points, and to output position sensor data representing the detected position;

one or more processors, configured to:

control the unmanned aerial vehicle to rotate about its z-axis;

receive magnetometer data comprising a plurality of z-axis directional measurements taken during the rotation about the z-axis;

receive position sensor data and determine from at least the position sensor data a magnetic field inclination of the detected position;

determine a z-axis magnetometer correction value as a difference between the received magnetometer data for the z-axis and the determined magnetic field inclination;

wherein the one or more processors are further configured to receive magnetometer data comprising a plurality of x-axis directional measurements and y-axis directional measurements taken during the rotation about the z-axis, and to determine from the received x-axis directional measurements and y-axis directional measurements an x-axis magnetometer correction value and a y-axis magnetometer correction value;

wherein determining the z-axis magnetometer correction value comprises determining the z-axis magnetometer correction value based on the magnetic field inclination, a value corresponding to the x-axis magnetometer correction value, a value corresponding to the y-axis magnetometer correction value, and the plurality of z-axis directional measurements.

2. The unmanned aerial vehicle of claim 1 , wherein the one or more processors are further configured to calibrate the magnetometer by the correction value.

3. The unmanned aerial vehicle of claim 1 , wherein the one or more processors are further configured to average the plurality of z-axis directional measurements to obtain an average magnitude of the detected magnetometer data for the z-axis, and wherein determining the z-axis magnetometer correction value as a difference between the received magnetometer data and the magnetic field inclination comprises comparing the averaged magnitude of the plurality of measurements to the magnetic field inclination.

4. A method of calibration comprising

detecting a magnitude of a magnetic field relative to a y-axis of an unmanned aerial vehicle;

controlling the unmanned aerial vehicle to rotate about its z-axis;

determining a plurality of z-axis directional magnetic field measurements during the rotation about the z-axis;

determining a position of the unmanned aerial vehicle relative to one or more reference points;

determining a magnetic field inclination corresponding to the detected position;

determining a z-axis correction value as a difference between the detected z-axis directional magnetic field measurements and the determined magnetic field inclination;

further comprising taking a plurality of x-axis directional measurements and y-axis directional during the rotation about the z-axis, and determining from the received x-axis directional measurements and y-axis directional measurements an x-axis magnetometer correction value and a y-axis magnetometer correction value;

wherein determining the z-axis magnetometer correction value comprises determining the z-axis magnetometer correction value based on the magnetic field inclination, a value corresponding to the x-axis magnetometer correction value, a value corresponding to the y-axis magnetometer correction value, and the plurality of z-axis directional measurements.

5. The method of calibration of claim 4 , further comprising calibrating the magnetometer by the correction value.

6. The method of calibration of claim 4 , further comprising averaging the plurality of z-axis directional measurements to obtain an average magnitude of the z-axis directional magnetic field measurements; and wherein determining the z-axis magnetometer correction value comprises comparing an averaged magnitude of the plurality of measurements to the magnetic field inclination.