Add magnetometer thermal calibration/compensation.

[mcsauder]

Describe problem solved by this pull request

This PR extends the thermal compensation to include magnetometers. Sensor ordering following the convention accel, gyro, mag, baro is also standardized across files in this PR.

Describe your solution

Data taken from an IST8310 magnetometer standard with the pixhawk4 and pixhawk4 mini shows a change in measured values from 0C to 45C by almost ~10uTesla (0.1Gauss). The typical earth magnetic field strength is ~60uTesla, so the observed shift is significant against what is being measured and more significant in areas of the earth with weaker magnetic field strength.

Test data / coverage

Flight tested with calibration values applied at ambient (~21C): https://review.px4.io/plot_app?log=6335c430-828b-4f7e-8404-ba7832585ada
After cold soaking to ~7C and temperature climbing to ~17C: https://review.px4.io/plot_app?log=6335c430-828b-4f7e-8404-ba7832585ada

Additional context

Most magnetometers do not have an integrated temperature sensor, so this PR utilizes the primary barometer temperature value as the magnetometer temperature. If there is a better alternative we can certainly use a different source (such as the IMU).

Let me know if you have questions or feedback on this PR. Thanks!

-Mark

[dagar]

Overall this looks good, but I really don't think we should be plumbing in random baro temperature in a magnetometer driver just for a temperature.

Should we do something to make the temperature source configurable (at the level of the compensation)?

[mcsauder]

Should we do something to make the temperature source configurable (at the level of the compensation)?

Yes. Good suggestion. I'll work on that. Thanks @dagar !

[dagar]

Overall looks fine, but I do have a few suggestions for later

• Tools/process_sensor_caldata.py
  • remove initial (and probably final) garbage data
  • decode device ids
  • verify onboard cal gives same results as offline script
• split sensor_corrections for accel, gyro, baro, mag and publish per instance on temperature change
• calibration only when the vehicle/board is still (conservative monitoring of accel/gyro)
• heavily filter onboard calibration raw sensor data

[mcsauder]

@dagar , comments addressed, thank you! Squashed and rebased.

[hamishwillee]

@mcsauder When this goes in, we will need to update http://docs.px4.io/main/en/advanced_config/sensor_thermal_calibration.html#thermal-calibration-and-compensation - I assume this will be in the release after PX4 v1.15, and that you will take care of initial update (might be as small as just removing the note up the top of that doc.)