Auto compass declination questions

General
1

From what I understand, it’d be advisable to do a compass calibration if you jumped in the car and drove quite some distance away from home, for example 100km, to do flying/driving/floating/sinking with Ardupilot. I was wondering how “auto” the autodeclination really is…
I have the auto declination option set and there seems to be no issue since I’ve not experienced any directional issues. I’ve looked over the copter docs and everything else I could find on auto declination but I’m left with a couple of questions.

  1. is the auto declination table baked into the firmware, and therefore fixed until the next firmware update? Could be an issue if you’re running 2 year old firmware!

  2. is the table updated dynamically from an external source either during operation, or just during compass calibration? (which leads to the next question)

  3. if updated dynamically, does that mean the ground station used for calibration needs an internet connection, or is it somehow like the GPS almanac and is updated as if by magic?

Back to my scenario - Driving away from home some distance where I dont normally operate, will I be able to leave Ardupilot (arducopter in my case) sit powered up for a few minutes to sort its self out in regards to the compass and declination?
Or do I need to have a groundstation, internet connection and perform a compass calibration.

The alternative is: do nothing, power up and fly as per normal, the auto declination sorts out everything.

2

The declination look-up table is indeed integral to the firmware. It’s not dynamically updated it’s hard coded. Declination changes very slightly over time, a couple years is not significant. A decade is hardly significant. For example where I am declination is changing ~2’W per year. 16yrs for a 0.5° change. This depends on where you are but you get the idea.

So, do nothing and let auto declination take care of it!

Compass calibration is not related to declination. It determines error offsets from vehicle local magnetic anomalies. The only time you need to re-do the compass calibration is if something changes on the vehicle that would effect the magnetic field. Wire routing, change in electronics, battery, etc.

3

Great, thanks a lot Dave.

4

I see a lot about the poles moving lately:

Does the declination table need updating in ardupilot? I understand declination changes are relatively slow to occur, just checking though…

5

I have had issues with auto declination - toilet boweling in particular. I generally switch it off these days as when I look at the auto values they do not match what google is telling me. May be something to do with the northern location of the UK.