EKF3: allow earth-frame fields to be estimated with an origin but no GPS

[Williangalvani]

This is my attempt at fixing #18229

Here's a log using it:
00000228.zip
I am using a script to set the origin so we can use the earth field database.

I can see that XKF2 fields are all populated for magnetic field in body frame and earth frame.

I am not sure of what else to look at, though. magnetic field innovations seem bad, but at least they exist?

[rmackay9]

Hi, if the issue is the earth magnetic field (aka WMM) is not being estimated then the EKF also shouldn't be trying to use the WWM to reject the compass, instead it should accept it I think.

As a side note, it's naughty that the EKF is using the GPS status at all when estimating the WWM. This presumably means the same problem could happen when using a non-GPS navigation source while also using a compass which is very possible (e.g. Beacons).

[lixiaowei123]

I have been saying that there is a bug in the estimation of EKF3 acceleration velocity increment offset

[lixiaowei123]

@rmackay9 You can view all the latest version logs to see if this is sometimes very large, and normally it should not exceed 0.3

[rmackay9]

As discussed on the dev call we should investigate why the EKF3 is unable to fuse the compass when it doesn't have a position estimate. It really should be able to although it won't be as accurate.

[tridge]

could be a common function with the code in readGpsData()

[tridge]

maybe setEarthFieldFromLocation()

[rmackay9]

We discussed on the July 2nd dev call and decided that we should move the shared code to a new function and then call it from within setOrigin and readGPSData.