World Magnetic Model needs to be updated (after January 30)
« on: January 13, 2019, 06:24:40 pm »
This amount of mag angle error may or may not be important to the operation of LibrePilot GPS flight modes.

GPS flight modes use the GPS to know where the aircraft is, but they use the mag to know what direction it is pointed in.  If it thinks it is pointed north and it wants to go north it issues a "go forward" command.  If it was actually pointed east when it thought it was pointed north, it will now be farther away than it was to start with and you have a "fly away".  That is for very large errors.  For smaller errors you get oscillations.  For errors below some limit (probably a few degrees) it handles it and all you get is a slightly curved deviation from straight flight.  That is why (in 16.09) we require a green mag to arm in GPS flight modes.

The LibrePilot code's 2015 World Magnetic Model (apparently the WMM is updated every 5 years) was supposed to last until 2020 but magnetic north has drifted and according to the articles:
"The magnetic pole is moving so quickly that it has forced the world's geomagnetism experts into a rare move."
"They realized that it was so inaccurate that it was about to exceed the acceptable limit for navigational errors."

"... the release of the corrected World Magnetic Model, which should restore accuracy through the end of 2019, has now been postponed from January 15th to January 30th -- 'due to the ongoing US government shutdown.' "

https://www.nature.com/articles/d41586-019-00007-1
https://science.slashdot.org/story/19/01/13/0427222/earths-magnetic-field-is-acting-up-and-geologists-dont-know-why

There is a small chance that this is related to some LibrePilot GPS mode aircraft oscillations.

I have convinced myself that simply making a small angle change to aux mag settings (Attitude->Magnetometer->Orientation) will not work to fix this because that rotation is in the model's frame of reference, not the earth's frame of reference.