This provides the calling vehicle software the abiity to request the EKF to not use GPS.
An integer is returned that indicates the type of operation available:
0 = request rejected (request will only be accepted if the EKF is in static mode, eg pre-armed)
1 = request accepted, attitude, vertical velocity and position estimates available
2 = request accepted, attitude, height rate, height, horizontal velocity and relative position estimates available
This takes into account the inter-sampling delay between the flow driver and the APM software which depends on the rate at which the dirver is being checked. This is 50Hz for plane and rover, and 200Hz for Copter.
This patch reduces the level of 5Hz and 10Hz 'pulsing' heard in motors due to GPS and altimeter fusion which cause a small 5Hz and 10Hz ripple on the output under some conditions. Attitude, velocity and position state corrections from GPS, altimeter and magnetometer measurements are applied incrementally in the interval from receiving the measurement to the predicted time of receipt of the next measurement. Averaging of attitude state corrections is not performed during periods of rapid rotation.
Time stamps are now explicitly initialised to the current IMU time to avoid unwanted activation of timeout logic on filter start and the various calls to the hal.scheduler->millis() object have been consolidated.
Unused variables have been removed
If the inertial solution velocity or position needs to be reset to the GPS, the stored state history for the corresponding states should also be reset.
Otherwise the next GPS measurement will be compared to an invalid previous state and will be rejected.
The position state should be reset to a GPS position corrected for velocity and measurement latency. This will make a noticeable difference for high speed flight vehicles, eg 11m at 50m/s
Re-initialisation of the magnetic field states and yaw angle is now only performed a maximum of two times after start-up.
Once when coming out of static modefor the first time (first arm event)
Again (for copter only) when the altitude gain above the arming altitude exceeds 1.5m
this prevents magnetic interference present at arming (eg arming on a metal roof)from corrupting the magnetic field states enough to cause bad heading errors and toilet bowling on copter
(Plane Only) If the yaw and GPS heading disagree by more than 45 degrees on takeoff, then the magnetometer is declared as failed. The heading is then reset based on the difference between GPS ground track and stgate velocity vector.
Magnetometer fusion uses corrected data and bias states are initialised to zero. This allows the compass to be switched in flight.
For persistent compass errors that trigger a timeout, the compass is not permanently failed, however for non-forward fly vehicles the compass weighting is reduced.
