The magnetic field states are reset once at 1.5 metres and again at 5 metres. This height check was using the height at the first arm event as the reference. In the situation where there is baro drift and extgended time between the first arm event and flight, this can cause the magnetic field state to be reset when on the ground. If this happens when flying off a metallic surface, the resultant heading errors can cause sever toilet bowling.
Improve the quality of the GPS required to set an EKF origin
Eliminate repeated update of origin height - origin height updates once when EKF origin is set.
Operation in GPS mode is linked to setting of origin
The maximum time copters can reject GPS has been reduced from 10 to 7 seconds as flight logs have show that inertial dead reckoning with vibration and calibration errors is not good enough to support 10 seconds without aiding.
This patch causes the EKF to update the height of its origin each time it receives a valid GPs message whislt disarmed.
The resultant EKF origin height represents the height of the zero baro alt datum relative to the GPS height datum.
Flight tests have shown that the magnetic field distortion associated with flight from steel structures can extend 3m or higher. To counteract this, a second and final yaw and magnetic field alignment has been added which is activated when the height exceeds 5m for the first time.
Logic used to delay optical flow and airspeed fusion to prevent it occurring on the same time step as magnetometer fusion has been removed. This is no longer required to efficiency improvements made at the firmware level.
Improvements in PX4 firmware have reduced the computational load and mkae the previous practicwe of splitting magnetometer and optical flow fusion across multiple time steps unnecessary and make it possible to perform a covariance prediction prior to fusing data on the same time step. This patch:
1) Ensures that a covariance prediction is always performed prior to fusion of any observation
2) Removes the splitting of magnetometer fusion so that fusion of the X,Y and Z components occurs on the same time time step
3) Removes the splitting of optical flow fusion so that fusion of X and Y components occurs on the same time step
UBlox receivers report an estimate of the speed accuracy that tests show correlates well to speed glitches. Using this to scale the GPS velocity observation noise will reduce the effect of bad GPS velocity data.
If the vehicle moves significantly or the GPS changes position significantly pre-armed, then the GPS glitch logic was being invoked when the first GPs measurements were fused. This patch resets the position to the GPS when the vehicle arms.
Due to the way that gyro calibration is done, the EKF could be effectively not run for up to 30 seconds in extreme cases, making it possible that the GPS would be failed on arming and the copter put into a non-GPS mode.
the longer term solution is to update the gyro calibration so that it does not hold up other processing. the short tyermfix in thsi patch is to look for evidence of a 3D lock in the last received GPS message.
This fixes a bug that meant that once the EKF had started up in a non-GPS mode, it would no longer read the GPS and therefore would never be able to use GPS again until reset.
Paul Riseborough
myly10
Andrew Tridgell
Jonathan Challinger
Randy Mackay
Grant Morphett