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.
we must not update _gyro_offset[] until we have completed calibration
of that gyro, or we will end up using the new offsets when asking for
the raw gyro vector
