When at rest, directly fuse the gyro data as an observation of its bias.
This allows to strongly observe the gyro biases without having to fuse a
constant heading that makes the ekf too confident about its heading.
Tests showed that sideslip fusion often starts just before airspeed
fusion, resetting the wind states to 0 instead of using the airspeed
data. A quick look at the wind uncertainty allows to know if the current
wind estimate is meaningful or if we should rather reset it using the
airspeed data.
- EKF isTimedOut(), isRecent(), and isNewestSampleRecent() need to handle the case where the timestamp has never been set
- reset() more thoroughly reset fields (mainly impacts unit tests)
- refactor all EKF backend output predictor pieces into new OutputPredictor class
- output states are now calculated immediately with new high rate IMU rather than after EKF update
- IMU delayed sample is passed as around as control data to avoid storing an extra copy and make the requirement clear
- move EV yaw and EV position to new state machines
- EV yaw and EV pos now configured via EKF2_EV_CTRL (migrated from EKF2_AID_MASK)
- new EV position offset estimator to enable EV position while GPS position is active (no more EV pos delta fusion)
- yaw_align now strictly means north (no more rotate external vision aid mask)
- automatic switching between EV yaw, and yaw align north based on GPS quality
- respect new EKF2_EV_CTRL parameter for VPOS usage
- EV hgt rotate EV position before usage (there's often a small offset in frames)
- EV hgt reset use proper EV velocity body frame
- try to keep EV hgt and EV vel state machines consistent
- small incremental piece of https://github.com/PX4/PX4-Autopilot/pull/19128
- with Ekf::initialiseFilter() resetting _time_last_hagl_fuse the terrain estimate was technically valid regardless of any range or flow data availability and as a result optical flow fusion is able to start and stay active
- only consider terrain estimate valid based on control status flags and recent fusion
- working towards keeping all height source (baro/ev/gnss/rng) handling as consistent as possible, possibly refactoring these out into separate classes later
bresch