# Magnetometer Calibration

## Definition

The INS component of the Applanix APX-15 GNSS-INS sensor utilizes a magnetometer, in addition to other onboard sensors, to aid in heading and attitude determination by measuring the vector component of the Earth’s magnetic field.&#x20;

"The MAG is only used for very coarse heading initialization so the absolute accuracy of the MAG heading isn't vital to performance. The main heading alignment comes from the \[dynamic alignment procedure] while in-flight." - Applanix Support

Magnetometer calibrations are performed in-flight in just a few minutes, with no external setup beyond the aircraft and payload required.

## Frequency

1. At least once yearly.
2. If any physical changes are made to the payload/configuration/installation.
3. When the magnetic declination changes more than 10-15 degrees (typically corresponding to several hundred miles of range from last calibration).
   * See map here for more information:

{% embed url="<https://www.ncei.noaa.gov/products/world-magnetic-model>" %}

## Requirements

* The calibration requires for the unit to be rotated at least 3 times clock wise and 3 times counter clock wise around the z-axis.&#x20;
* The calibration algorithm is initiated automatically when the receiver is rotated about the Z‐axis a minimum of 0.6 degrees / second.
* The maximum angular rate cannot exceed 40 degrees / second. It should therefore take at least 9 seconds to complete a full 360 degree rotation about one axis.
* Don’t move further away from power on location than 50m for calibration procedure.

## Instructions

To begin a magnetometer calibration:

1. Turn on the aircraft and power the payload.
   1. Aircraft should be far from buildings, cars, or other metal objects.
2. Let the UAV **sit static for at least 1 minute**.
3. Take off and hover in place at 10-25m AGL.
4. Begin rotating (yawing) the UAV clockwise, completing **each 360 degree rotation in no less than 9 seconds.**
5. Complete **at minimum** 3 rotations clockwise.
6. Repeat rotations counter-clockwise.
7. Land the UAV&#x20;

To check that the calibration was completed properly:

1. Connect an ethernet cable between your laptop and the system's GNSS ethernet port&#x20;
2. Go to IP address 10.0.65.100 in a browser&#x20;
3. If prompted, Username: admin; Password: password&#x20;
4. Receiver Status -> INS Status
5. Ensure the latest calibration date and time match today’s date&#x20;
   1. If the date/time has not updated, power off the system, wait at least 10 minutes, then repeat the calibration.
