Range finder and optical flow data can drop-out and be reliable very close to ground. these patches enable the takeoff to be more relaibly detected and constrain optical flow navigation drift in the first part of takeoff.
Falls back to baro if range finder is unavailable
Adds parameter enabling user to select which height source (baro or range finder) will be used during optical flow nav.
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
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.
This enables the filter to report the last known position after disarm.
The LLH location of the filters NED origin is published and should be logged every time the vehicle is armed to assist with post-flight trajectory reconstruction.
The LLH location of the filters NED origin can be set externally whilst the vehicle is disarmed.
The two state auxiliary EKF has been replaced with a single state filter that only estimates terrain offset. The new filter fuses a optical flow line of sight rate scalar (length of the optical flow LOS rate vector) which provides a terrain offset estimate that is less affected by yaw errors.
Estimation of focal length scale factor error in flight wasn't accurate enough and will be replaced with a pre-flight intrinsic sensor calibration procedure as the scale factor error does not change over time provided the lens assembly is not adjusted.
AP_NavEKF: Remove unwanted printf
The terrain offset solution status is usable for a short period of time without state updates so a timeout has been added which prevents the rapid changes in solution status due to short duration sensor read errors.
Non user adjustable parameters are now declared as 'const' in the header.
The _ prefix has been removed from non user adjustable tuning parameters.
We use a function call rather than a constructor to initialise variables because it enables the filter to be re-started in flight if necessary.
For consistency some signed integer type declarations have been changed to unsigned where appropriate.
Required to prevent acquisition of GPS mid flight causing unwanted change in position and velocity
A distinction has been mad between the arm and disarm transition and the decision to use position hold mode (formerly static mode)
When regaining GPS after a timeout, an offset is applied when fusing GPS velocity so that GPS velocity and position data as fused by the EKF is kinematically consistent.
This velocity offset is also accounted for when fusing air data so that wind estimates are not corrupted when the GPS position offset is being pulle back to zero.
The intended behaviour is that the EKF position will be pulled back to the GPS position at a rate of 5m/s for planes and 1 m/s for copters. This avoids large deviations in trajectory when GPS is regained.
1) Un-used public methods to report height and position drifting have been removed
2) A time-out has been added to the airspeed innovation consistency check so that if we are relying on airspeed to constrain velocity drift, a filter divergence or other fault that causes the airspeed to be continually rejected will trigger a change in health status.
3) A timeout of velocity, position or height measurements does not cause a filter fault to be reported. Timeouts can be due to sensor errors and do not necessarily indicate that the filter has failed.
4) Time-outs of various measurements are used to present a consolidated bitmask which inidicates which parts of the solution can be used, eg attitude, height, velocity, relative position, absolute position, etc.
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
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.
GPS measurement variance is doubled if only 5 satellites, and quadrupled if 4 or less.
The GPS glitch rejection thresholds remain the same
This will reduce the impact of GPS glitches on attitude.
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 various calls to the hal.scheduler->millis() object have been consolidated.
If the vehicle can fly without a compass (a fly forward vehicle)
then if the compass times out (large errors for more than 10 seconds,
then it will be declared permanently failed and will not be
used until the filter is reset
Divergence is now detected by looking for very large changes in the gyro
bias. This will cause the filter to be reset and declared unhealthy for
10 seconds.
Don't reset filterDiverged status immediately during reset
Set filterDiverged true if covariance blows up
Add fault status reporting
This will enable in-flight magnetometer calibration to be inhibited unconditionally,
This is required for long balloon carriage flights where ground speed can be high
enough to put it into in-air state, but with very poor observability of magnetic field
states causing bad state estimates and heading offsets to develop over time.
The covariance matrix no longer has rows and columns artificially zeroed when in static
mode. Instead booleans indicating whether wind or magentic field state estimation is
active are used to:
a) Set the process noise on these states to zero to stop their variances from increasing
unchecked when not being updated, and
b) Turn off updates for these states when measurement fusion is being performed.
This reduces the likelihood of a badly conditioned covariance matrix forming
during static mode operation.
A filter divergence check has also been added that will declare the filter unhealthy if
position, velocity and magnetic field observations are all failing their innovation
consistency checks. This unhealthy status will persist for 10 seconds after the
condition clears.
AP_NavEKF: Remove unnecessary zeroing of wind covariances
A magnetometer axis that fails the innovation consistency check will cause
all axes not to be used. If this condition continues for 10 seconds, a
magnetometer timeout condition will be declared. When the timeout has
occurred, if it is not a fly forward vehicle, then individual channels
will be used again, but with a reduced weighting.
This patch also cleans up the logic associated with use of the synthetic
sideslip measurement so that it can never be used for a non fly-forward
vehicle type
This patch adds functionality that initialises the wind-speed vector to the
reciprocal of the ground speed vector, and scaled to 6 m/s. On average this gives
a better initial wind velocity estimate on launch by assuming:
a) launch will be into wind
b) wind speed is equal to global average
It also helps prevent a headwind causing initial underestimation of airspeed
causing high autopilot gains and limit cycles on climb-out, until first
turn when the EKF is able to estimate the wind.
Randy Mackay
Paul Riseborough
Jonathan Challinger
Andrew Tridgell
Grant Morphett
Andrew Tridgell
Emile Castelnuovo