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/**
* @file control.cpp
* Control functions for ekf attitude and position estimator.
*
* @author Paul Riseborough <p_riseborough@live.com.au>
*
*/
#include "../ecl.h"
#include "ekf.h"
#include <mathlib/mathlib.h>
void Ekf::controlFusionModes()
{
// Store the status to enable change detection
_control_status_prev.value = _control_status.value;
// monitor the tilt alignment
if (!_control_status.flags.tilt_align) {
// whilst we are aligning the tilt, monitor the variances
Vector3f angle_err_var_vec = calcRotVecVariances();
// Once the tilt variances have reduced to equivalent of 3deg uncertainty, re-set the yaw and magnetic field states
// and declare the tilt alignment complete
if ((angle_err_var_vec(0) + angle_err_var_vec(1)) < sq(math::radians(3.0f))) {
_control_status.flags.tilt_align = true;
_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
// send alignment status message to the console
if (_control_status.flags.baro_hgt) {
ECL_INFO("EKF aligned, (pressure height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
} else if (_control_status.flags.ev_hgt) {
ECL_INFO("EKF aligned, (EV height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
} else if (_control_status.flags.gps_hgt) {
ECL_INFO("EKF aligned, (GPS height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
} else if (_control_status.flags.rng_hgt) {
ECL_INFO("EKF aligned, (range height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
} else {
ECL_ERR("EKF aligned, (unknown height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
}
}
}
// check for intermittent data (before pop_first_older_than)
const baroSample &baro_init = _baro_buffer.get_newest();
_baro_hgt_faulty = !((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
const gpsSample &gps_init = _gps_buffer.get_newest();
_gps_hgt_intermittent = !((_time_last_imu - gps_init.time_us) < 2 * GPS_MAX_INTERVAL);
// check for arrival of new sensor data at the fusion time horizon
_gps_data_ready = _gps_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_gps_sample_delayed);
_mag_data_ready = _mag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_mag_sample_delayed);
_delta_time_baro_us = _baro_sample_delayed.time_us;
_baro_data_ready = _baro_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_baro_sample_delayed);
// if we have a new baro sample save the delta time between this sample and the last sample which is
// used below for baro offset calculations
if (_baro_data_ready) {
_delta_time_baro_us = _baro_sample_delayed.time_us - _delta_time_baro_us;
}
// calculate 2,2 element of rotation matrix from sensor frame to earth frame
// this is required for use of range finder and flow data
_R_rng_to_earth_2_2 = _R_to_earth(2, 0) * _sin_tilt_rng + _R_to_earth(2, 2) * _cos_tilt_rng;
// Get range data from buffer and check validity
_range_data_ready = _range_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_range_sample_delayed);
checkRangeDataValidity();
if (_range_data_ready && !_rng_hgt_faulty) {
// correct the range data for position offset relative to the IMU
Vector3f pos_offset_body = _params.rng_pos_body - _params.imu_pos_body;
Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
_range_sample_delayed.rng += pos_offset_earth(2) / _R_rng_to_earth_2_2;
}
// We don't fuse flow data immediately because we have to wait for the mid integration point to fall behind the fusion time horizon.
// This means we stop looking for new data until the old data has been fused.
if (!_flow_data_ready) {
_flow_data_ready = _flow_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_flow_sample_delayed)
&& (_R_to_earth(2, 2) > _params.range_cos_max_tilt);
}
// check if we should fuse flow data for terrain estimation
if (!_flow_for_terrain_data_ready && _flow_data_ready && _control_status.flags.in_air) {
// only fuse flow for terrain if range data hasn't been fused for 5 seconds
_flow_for_terrain_data_ready = (_time_last_imu - _time_last_hagl_fuse) > 5 * 1000 * 1000;
// only fuse flow for terrain if the main filter is not fusing flow and we are using gps
_flow_for_terrain_data_ready &= (!_control_status.flags.opt_flow && _control_status.flags.gps);
}
_ev_data_ready = _ext_vision_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_ev_sample_delayed);
_tas_data_ready = _airspeed_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_airspeed_sample_delayed);
// check for height sensor timeouts and reset and change sensor if necessary
controlHeightSensorTimeouts();
// control use of observations for aiding
controlMagFusion();
controlOpticalFlowFusion();
controlGpsFusion();
controlAirDataFusion();
controlBetaFusion();
controlDragFusion();
controlHeightFusion();
// For efficiency, fusion of direct state observations for position and velocity is performed sequentially
// in a single function using sensor data from multiple sources (GPS, baro, range finder, etc)
controlVelPosFusion();
// Additional data from an external vision pose estimator can be fused.
controlExternalVisionFusion();
// Additional NE velocity data from an auxiliary sensor can be fused
controlAuxVelFusion();
// check if we are no longer fusing measurements that directly constrain velocity drift
update_deadreckoning_status();
}
void Ekf::controlExternalVisionFusion()
{
// Check for new external vision data
if (_ev_data_ready) {
// if the ev data is not in a NED reference frame, then the transformation between EV and EKF navigation frames
// needs to be calculated and the observations rotated into the EKF frame of reference
if ((_params.fusion_mode & MASK_ROTATE_EV) && ((_params.fusion_mode & MASK_USE_EVPOS) || (_params.fusion_mode & MASK_USE_EVVEL)) && !_control_status.flags.ev_yaw) {
// rotate EV measurements into the EKF Navigation frame
calcExtVisRotMat();
}
// external vision aiding selection logic
if (_control_status.flags.tilt_align && _control_status.flags.yaw_align) {
// check for a external vision measurement that has fallen behind the fusion time horizon
if ((_time_last_imu - _time_last_ext_vision) < (2 * EV_MAX_INTERVAL)) {
// turn on use of external vision measurements for position
if (_params.fusion_mode & MASK_USE_EVPOS && !_control_status.flags.ev_pos) {
_control_status.flags.ev_pos = true;
resetPosition();
ECL_INFO("EKF commencing external vision position fusion");
}
// turn on use of external vision measurements for velocity
if (_params.fusion_mode & MASK_USE_EVVEL && !_control_status.flags.ev_vel) {
_control_status.flags.ev_vel = true;
resetVelocity();
ECL_INFO("EKF commencing external vision velocity fusion");
}
if ((_params.fusion_mode & MASK_ROTATE_EV) && !(_params.fusion_mode & MASK_USE_EVYAW)
&& !_ev_rot_mat_initialised) {
// Reset transformation between EV and EKF navigation frames when starting fusion
resetExtVisRotMat();
_ev_rot_mat_initialised = true;
}
}
}
// external vision yaw aiding selection logic
if (!_control_status.flags.gps && (_params.fusion_mode & MASK_USE_EVYAW) && !_control_status.flags.ev_yaw && _control_status.flags.tilt_align) {
// don't start using EV data unless daa is arriving frequently
if (_time_last_imu - _time_last_ext_vision < 2 * EV_MAX_INTERVAL) {
// reset the yaw angle to the value from the observation quaternion
// get the roll, pitch, yaw estimates from the quaternion states
Quatf q_init(_state.quat_nominal);
Eulerf euler_init(q_init);
// get initial yaw from the observation quaternion
const extVisionSample &ev_newest = _ext_vision_buffer.get_newest();
Quatf q_obs(ev_newest.quat);
Eulerf euler_obs(q_obs);
euler_init(2) = euler_obs(2);
// save a copy of the quaternion state for later use in calculating the amount of reset change
Quatf quat_before_reset = _state.quat_nominal;
// calculate initial quaternion states for the ekf
_state.quat_nominal = Quatf(euler_init);
uncorrelateQuatStates();
// adjust the quaternion covariances estimated yaw error
increaseQuatYawErrVariance(sq(fmaxf(_ev_sample_delayed.angErr, 1.0e-2f)));
// calculate the amount that the quaternion has changed by
_state_reset_status.quat_change = _state.quat_nominal * quat_before_reset.inversed();
// add the reset amount to the output observer buffered data
for (uint8_t i = 0; i < _output_buffer.get_length(); i++) {
_output_buffer[i].quat_nominal = _state_reset_status.quat_change * _output_buffer[i].quat_nominal;
}
// apply the change in attitude quaternion to our newest quaternion estimate
// which was already taken out from the output buffer
_output_new.quat_nominal = _state_reset_status.quat_change * _output_new.quat_nominal;
// capture the reset event
_state_reset_status.quat_counter++;
// flag the yaw as aligned
_control_status.flags.yaw_align = true;
// turn on fusion of external vision yaw measurements and disable all magnetometer fusion
_control_status.flags.ev_yaw = true;
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_dec = false;
// save covariance data for re-use if currently doing 3-axis fusion
if (_control_status.flags.mag_3D) {
save_mag_cov_data();
_control_status.flags.mag_3D = false;
}
ECL_INFO("EKF commencing external vision yaw fusion");
}
}
// determine if we should start using the height observations
if (_params.vdist_sensor_type == VDIST_SENSOR_EV) {
// don't start using EV data unless data is arriving frequently
if (!_control_status.flags.ev_hgt && ((_time_last_imu - _time_last_ext_vision) < (2 * EV_MAX_INTERVAL))) {
setControlEVHeight();
resetHeight();
}
}
// determine if we should use the vertical position observation
if (_control_status.flags.ev_hgt) {
_fuse_height = true;
}
// determine if we should use the horizontal position observations
if (_control_status.flags.ev_pos) {
_fuse_pos = true;
// correct position and height for offset relative to IMU
Vector3f pos_offset_body = _params.ev_pos_body - _params.imu_pos_body;
Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
_ev_sample_delayed.posNED(0) -= pos_offset_earth(0);
_ev_sample_delayed.posNED(1) -= pos_offset_earth(1);
_ev_sample_delayed.posNED(2) -= pos_offset_earth(2);
// Use an incremental position fusion method for EV position data if GPS is also used
if (_params.fusion_mode & MASK_USE_GPS) {
_fuse_hpos_as_odom = true;
} else {
_fuse_hpos_as_odom = false;
}
if (_fuse_hpos_as_odom) {
if (!_hpos_prev_available) {
// no previous observation available to calculate position change
_fuse_pos = false;
_hpos_prev_available = true;
} else {
// calculate the change in position since the last measurement
Vector3f ev_delta_pos = _ev_sample_delayed.posNED - _pos_meas_prev;
// rotate measurement into body frame is required when fusing with GPS
ev_delta_pos = _ev_rot_mat * ev_delta_pos;
// use the change in position since the last measurement
_vel_pos_innov[3] = _state.pos(0) - _hpos_pred_prev(0) - ev_delta_pos(0);
_vel_pos_innov[4] = _state.pos(1) - _hpos_pred_prev(1) - ev_delta_pos(1);
// observation 1-STD error, incremental pos observation is expected to have more uncertainty
_posObsNoiseNE = fmaxf(_ev_sample_delayed.posErr, 0.5f);
}
// record observation and estimate for use next time
_pos_meas_prev = _ev_sample_delayed.posNED;
_hpos_pred_prev(0) = _state.pos(0);
_hpos_pred_prev(1) = _state.pos(1);
} else {
// use the absolute position
Vector3f ev_pos_meas = _ev_sample_delayed.posNED;
if (_params.fusion_mode & MASK_ROTATE_EV) {
ev_pos_meas = _ev_rot_mat * ev_pos_meas;
}
_vel_pos_innov[3] = _state.pos(0) - ev_pos_meas(0);
_vel_pos_innov[4] = _state.pos(1) - ev_pos_meas(1);
// observation 1-STD error
_posObsNoiseNE = fmaxf(_ev_sample_delayed.posErr, 0.01f);
// check if we have been deadreckoning too long
if ((_time_last_imu - _time_last_pos_fuse) > _params.reset_timeout_max) {
// don't reset velocity if we have another source of aiding constraining it
if (((_time_last_imu - _time_last_of_fuse) > (uint64_t)1E6) && ((_time_last_imu - _time_last_vel_fuse) > (uint64_t)1E6)) {
resetVelocity();
}
resetPosition();
}
}
// innovation gate size
_posInnovGateNE = fmaxf(_params.ev_pos_innov_gate, 1.0f);
}else{
_vel_pos_innov[3] = 0.0f;
_vel_pos_innov[4] = 0.0f;
}
// determine if we should use the velocity observations
if (_control_status.flags.ev_vel) {
_fuse_hor_vel = true;
_fuse_vert_vel = true;
Vector3f velNED_aligned{_ev_sample_delayed.velNED};
// rotate measurement into correct earth frame if required
if (_params.fusion_mode & MASK_ROTATE_EV) {
velNED_aligned = _ev_rot_mat * _ev_sample_delayed.velNED;
}
// correct velocity for offset relative to IMU
Vector3f ang_rate = _imu_sample_delayed.delta_ang * (1.0f / _imu_sample_delayed.delta_ang_dt);
Vector3f pos_offset_body = _params.ev_pos_body - _params.imu_pos_body;
Vector3f vel_offset_body = cross_product(ang_rate, pos_offset_body);
Vector3f vel_offset_earth = _R_to_earth * vel_offset_body;
velNED_aligned -= vel_offset_earth;
_vel_pos_innov[0] = _state.vel(0) - velNED_aligned(0);
_vel_pos_innov[1] = _state.vel(1) - velNED_aligned(1);
_vel_pos_innov[2] = _state.vel(2) - velNED_aligned(2);
// check if we have been deadreckoning too long
if ((_time_last_imu - _time_last_vel_fuse) > _params.reset_timeout_max) {
// don't reset velocity if we have another source of aiding constraining it
if (((_time_last_imu - _time_last_of_fuse) > (uint64_t)1E6) && ((_time_last_imu - _time_last_pos_fuse) > (uint64_t)1E6)) {
resetVelocity();
}
}
// observation 1-STD error
_velObsVarNED(2) = _velObsVarNED(1) = _velObsVarNED(0) = fmaxf(_ev_sample_delayed.velErr, 0.01f);
// innovation gate size
_vvelInnovGate = _hvelInnovGate = fmaxf(_params.ev_vel_innov_gate, 1.0f);
}
// Fuse available NED position data into the main filter
if (_fuse_height || _fuse_pos || _fuse_hor_vel || _fuse_vert_vel) {
fuseVelPosHeight();
_fuse_vert_vel = _fuse_hor_vel = false;
_fuse_pos = _fuse_height = false;
_fuse_hpos_as_odom = false;
}
// determine if we should use the yaw observation
if (_control_status.flags.ev_yaw) {
fuseHeading();
}
} else if ((_control_status.flags.ev_pos || _control_status.flags.ev_vel)
&& (_time_last_imu >= _time_last_ext_vision)
&& ((_time_last_imu - _time_last_ext_vision) > (uint64_t)_params.reset_timeout_max)) {
// Turn off EV fusion mode if no data has been received
_control_status.flags.ev_pos = false;
_control_status.flags.ev_vel = false;
_control_status.flags.ev_yaw = false;
ECL_INFO("EKF External Vision Data Stopped");
}
}
void Ekf::controlOpticalFlowFusion()
{
// Check if on ground motion is un-suitable for use of optical flow
if (!_control_status.flags.in_air) {
// When on ground check if the vehicle is being shaken or moved in a way that could cause a loss of navigation
const float accel_norm = _accel_vec_filt.norm();
const bool motion_is_excessive = ((accel_norm > (CONSTANTS_ONE_G * 1.5f)) // upper g limit
|| (accel_norm < (CONSTANTS_ONE_G * 0.5f)) // lower g limit
|| (_ang_rate_mag_filt > _flow_max_rate) // angular rate exceeds flow sensor limit
|| (_R_to_earth(2,2) < cosf(math::radians(30.0f)))); // tilted excessively
if (motion_is_excessive) {
_time_bad_motion_us = _imu_sample_delayed.time_us;
} else {
_time_good_motion_us = _imu_sample_delayed.time_us;
}
} else {
_time_bad_motion_us = 0;
_time_good_motion_us = _imu_sample_delayed.time_us;
}
// Accumulate autopilot gyro data across the same time interval as the flow sensor
_imu_del_ang_of += _imu_sample_delayed.delta_ang - _state.gyro_bias;
_delta_time_of += _imu_sample_delayed.delta_ang_dt;
// New optical flow data is available and is ready to be fused when the midpoint of the sample falls behind the fusion time horizon
if (_flow_data_ready) {
// Inhibit flow use if motion is un-suitable or we have good quality GPS
// Apply hysteresis to prevent rapid mode switching
float gps_err_norm_lim;
if (_control_status.flags.opt_flow) {
gps_err_norm_lim = 0.7f;
} else {
gps_err_norm_lim = 1.0f;
}
// Check if we are in-air and require optical flow to control position drift
bool flow_required = _control_status.flags.in_air &&
(_is_dead_reckoning // is doing inertial dead-reckoning so must constrain drift urgently
|| (_control_status.flags.opt_flow && !_control_status.flags.gps && !_control_status.flags.ev_pos) // is completely reliant on optical flow
|| (_control_status.flags.gps && (_gps_error_norm > gps_err_norm_lim))); // is using GPS, but GPS is bad
if (!_inhibit_flow_use && _control_status.flags.opt_flow) {
// inhibit use of optical flow if motion is unsuitable and we are not reliant on it for flight navigation
bool preflight_motion_not_ok = !_control_status.flags.in_air && ((_imu_sample_delayed.time_us - _time_good_motion_us) > (uint64_t)1E5);
bool flight_motion_not_ok = _control_status.flags.in_air && !_range_aid_mode_enabled;
if ((preflight_motion_not_ok || flight_motion_not_ok) && !flow_required) {
_inhibit_flow_use = true;
}
} else if (_inhibit_flow_use && !_control_status.flags.opt_flow){
// allow use of optical flow if motion is suitable or we are reliant on it for flight navigation
bool preflight_motion_ok = !_control_status.flags.in_air && ((_imu_sample_delayed.time_us - _time_bad_motion_us) > (uint64_t)5E6);
bool flight_motion_ok = _control_status.flags.in_air && _range_aid_mode_enabled;
if (preflight_motion_ok || flight_motion_ok || flow_required) {
_inhibit_flow_use = false;
}
}
// Handle cases where we are using optical flow but are no longer able to because data is old
// or its use has been inhibited.
if (_control_status.flags.opt_flow) {
if (_inhibit_flow_use) {
_control_status.flags.opt_flow = false;
_time_last_of_fuse = 0;
} else if ((_time_last_imu - _time_last_of_fuse) > (uint64_t)_params.reset_timeout_max) {
_control_status.flags.opt_flow = false;
}
}
// optical flow fusion mode selection logic
if ((_params.fusion_mode & MASK_USE_OF) // optical flow has been selected by the user
&& !_control_status.flags.opt_flow // we are not yet using flow data
&& _control_status.flags.tilt_align // we know our tilt attitude
&& !_inhibit_flow_use
&& get_terrain_valid()) // we have a valid distance to ground estimate
{
// If the heading is not aligned, reset the yaw and magnetic field states
if (!_control_status.flags.yaw_align) {
_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
}
// If the heading is valid and use is not inhibited , start using optical flow aiding
if (_control_status.flags.yaw_align) {
// set the flag and reset the fusion timeout
_control_status.flags.opt_flow = true;
_time_last_of_fuse = _time_last_imu;
// if we are not using GPS or external vision aiding, then the velocity and position states and covariances need to be set
const bool flow_aid_only = !(_control_status.flags.gps || _control_status.flags.ev_pos);
if (flow_aid_only) {
resetVelocity();
resetPosition();
// align the output observer to the EKF states
alignOutputFilter();
}
}
} else if (!(_params.fusion_mode & MASK_USE_OF)) {
_control_status.flags.opt_flow = false;
}
// handle the case when we have optical flow, are reliant on it, but have not been using it for an extended period
if (_control_status.flags.opt_flow
&& !_control_status.flags.gps
&& !_control_status.flags.ev_pos) {
bool do_reset = ((_time_last_imu - _time_last_of_fuse) > _params.reset_timeout_max);
if (do_reset) {
resetVelocity();
resetPosition();
}
}
// Only fuse optical flow if valid body rate compensation data is available
if (calcOptFlowBodyRateComp()) {
bool flow_quality_good = (_flow_sample_delayed.quality >= _params.flow_qual_min);
if (!flow_quality_good && !_control_status.flags.in_air) {
// when on the ground with poor flow quality, assume zero ground relative velocity and LOS rate
_flowRadXYcomp.zero();
} else {
// compensate for body motion to give a LOS rate
_flowRadXYcomp(0) = _flow_sample_delayed.flowRadXY(0) - _flow_sample_delayed.gyroXYZ(0);
_flowRadXYcomp(1) = _flow_sample_delayed.flowRadXY(1) - _flow_sample_delayed.gyroXYZ(1);
}
} else {
// don't use this flow data and wait for the next data to arrive
_flow_data_ready = false;
}
}
// Wait until the midpoint of the flow sample has fallen behind the fusion time horizon
if (_flow_data_ready && (_imu_sample_delayed.time_us > _flow_sample_delayed.time_us - uint32_t(1e6f * _flow_sample_delayed.dt) / 2)) {
// Fuse optical flow LOS rate observations into the main filter only if height above ground has been updated recently
// but use a relaxed time criteria to enable it to coast through bad range finder data
if (_control_status.flags.opt_flow && ((_time_last_imu - _time_last_hagl_fuse) < (uint64_t)10e6)) {
fuseOptFlow();
_last_known_posNE(0) = _state.pos(0);
_last_known_posNE(1) = _state.pos(1);
}
_flow_data_ready = false;
}
}
void Ekf::controlGpsFusion()
{
// Check for new GPS data that has fallen behind the fusion time horizon
if (_gps_data_ready) {
// GPS yaw aiding selection logic
if ((_params.fusion_mode & MASK_USE_GPSYAW)
&& ISFINITE(_gps_sample_delayed.yaw)
&& _control_status.flags.tilt_align
&& (!_control_status.flags.gps_yaw || !_control_status.flags.yaw_align)
&& ((_time_last_imu - _time_last_gps) < (2 * GPS_MAX_INTERVAL))) {
if (resetGpsAntYaw()) {
// flag the yaw as aligned
_control_status.flags.yaw_align = true;
// turn on fusion of external vision yaw measurements and disable all other yaw fusion
_control_status.flags.gps_yaw = true;
_control_status.flags.ev_yaw = false;
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_dec = false;
// save covariance data for re-use if currently doing 3-axis fusion
if (_control_status.flags.mag_3D) {
save_mag_cov_data();
_control_status.flags.mag_3D = false;
}
ECL_INFO("EKF commencing GPS yaw fusion");
}
}
// fuse the yaw observation
if (_control_status.flags.gps_yaw) {
fuseGpsAntYaw();
}
// Determine if we should use GPS aiding for velocity and horizontal position
// To start using GPS we need angular alignment completed, the local NED origin set and GPS data that has not failed checks recently
bool gps_checks_passing = (_time_last_imu - _last_gps_fail_us > (uint64_t)5e6);
bool gps_checks_failing = (_time_last_imu - _last_gps_pass_us > (uint64_t)5e6);
if ((_params.fusion_mode & MASK_USE_GPS) && !_control_status.flags.gps) {
if (_control_status.flags.tilt_align && _NED_origin_initialised && gps_checks_passing) {
// If the heading is not aligned, reset the yaw and magnetic field states
// Do not use external vision for yaw if using GPS because yaw needs to be
// defined relative to an NED reference frame
if (!_control_status.flags.yaw_align || _control_status.flags.ev_yaw || _mag_inhibit_yaw_reset_req) {
_control_status.flags.ev_yaw = false;
_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
// Handle the special case where we have not been constraining yaw drift or learning yaw bias due
// to assumed invalid mag field associated with indoor operation with a downwards looking flow sensor.
if (_mag_inhibit_yaw_reset_req) {
_mag_inhibit_yaw_reset_req = false;
// Zero the yaw bias covariance and set the variance to the initial alignment uncertainty
setDiag(P, 12, 12, sq(_params.switch_on_gyro_bias * FILTER_UPDATE_PERIOD_S));
}
}
// If the heading is valid start using gps aiding
if (_control_status.flags.yaw_align) {
// if we are not already aiding with optical flow, then we need to reset the position and velocity
// otherwise we only need to reset the position
_control_status.flags.gps = true;
if (!_control_status.flags.opt_flow) {
if (!resetPosition() || !resetVelocity()) {
_control_status.flags.gps = false;
}
} else if (!resetPosition()) {
_control_status.flags.gps = false;
}
if (_control_status.flags.gps) {
ECL_INFO("EKF commencing GPS fusion");
_time_last_gps = _time_last_imu;
}
}
}
} else if (!(_params.fusion_mode & MASK_USE_GPS)) {
_control_status.flags.gps = false;
}
// Handle the case where we are using GPS and another source of aiding and GPS is failing checks
if (_control_status.flags.gps && gps_checks_failing && (_control_status.flags.opt_flow || _control_status.flags.ev_pos || _control_status.flags.ev_vel)) {
_control_status.flags.gps = false;
// Reset position state to external vision if we are going to use absolute values
if (_control_status.flags.ev_pos && !(_params.fusion_mode & MASK_ROTATE_EV)) {
resetPosition();
}
ECL_WARN("EKF GPS data quality poor - stopping use");
}
// handle the case when we now have GPS, but have not been using it for an extended period
if (_control_status.flags.gps) {
// We are relying on aiding to constrain drift so after a specified time
// with no aiding we need to do something
bool do_reset = ((_time_last_imu - _time_last_pos_fuse) > _params.reset_timeout_max)
&& ((_time_last_imu - _time_last_delpos_fuse) > _params.reset_timeout_max)
&& ((_time_last_imu - _time_last_vel_fuse) > _params.reset_timeout_max)
&& ((_time_last_imu - _time_last_of_fuse) > _params.reset_timeout_max);
// We haven't had an absolute position fix for a longer time so need to do something
do_reset = do_reset || ((_time_last_imu - _time_last_pos_fuse) > (2 * _params.reset_timeout_max));
if (do_reset) {
// use GPS velocity data to check and correct yaw angle if a FW vehicle
if (_control_status.flags.fixed_wing && _control_status.flags.in_air) {
// if flying a fixed wing aircraft, do a complete reset that includes yaw
_control_status.flags.mag_align_complete = realignYawGPS();
}
resetVelocity();
resetPosition();
_velpos_reset_request = false;
ECL_WARN("EKF GPS fusion timeout - reset to GPS");
// Reset the timeout counters
_time_last_pos_fuse = _time_last_imu;
_time_last_vel_fuse = _time_last_imu;
}
}
// Only use GPS data for position and velocity aiding if enabled
if (_control_status.flags.gps) {
_fuse_pos = true;
_fuse_vert_vel = true;
_fuse_hor_vel = true;
// correct velocity for offset relative to IMU
Vector3f ang_rate = _imu_sample_delayed.delta_ang * (1.0f / _imu_sample_delayed.delta_ang_dt);
Vector3f pos_offset_body = _params.gps_pos_body - _params.imu_pos_body;
Vector3f vel_offset_body = cross_product(ang_rate, pos_offset_body);
Vector3f vel_offset_earth = _R_to_earth * vel_offset_body;
_gps_sample_delayed.vel -= vel_offset_earth;
// correct position and height for offset relative to IMU
Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
_gps_sample_delayed.pos(0) -= pos_offset_earth(0);
_gps_sample_delayed.pos(1) -= pos_offset_earth(1);
_gps_sample_delayed.hgt += pos_offset_earth(2);
// calculate observation process noise
float lower_limit = fmaxf(_params.gps_pos_noise, 0.01f);
if (_control_status.flags.opt_flow || _control_status.flags.ev_pos) {
// if we are using other sources of aiding, then relax the upper observation
// noise limit which prevents bad GPS perturbing the position estimate
_posObsNoiseNE = fmaxf(_gps_sample_delayed.hacc, lower_limit);
} else {
// if we are not using another source of aiding, then we are reliant on the GPS
// observations to constrain attitude errors and must limit the observation noise value.
float upper_limit = fmaxf(_params.pos_noaid_noise, lower_limit);
_posObsNoiseNE = math::constrain(_gps_sample_delayed.hacc, lower_limit, upper_limit);
}
_velObsVarNED(2) = _velObsVarNED(1) = _velObsVarNED(0) = sq(fmaxf(_gps_sample_delayed.sacc, _params.gps_vel_noise));
// calculate innovations
_vel_pos_innov[0] = _state.vel(0) - _gps_sample_delayed.vel(0);
_vel_pos_innov[1] = _state.vel(1) - _gps_sample_delayed.vel(1);
_vel_pos_innov[2] = _state.vel(2) - _gps_sample_delayed.vel(2);
_vel_pos_innov[3] = _state.pos(0) - _gps_sample_delayed.pos(0);
_vel_pos_innov[4] = _state.pos(1) - _gps_sample_delayed.pos(1);
// set innovation gate size
_posInnovGateNE = fmaxf(_params.gps_pos_innov_gate, 1.0f);
_hvelInnovGate = _vvelInnovGate = fmaxf(_params.gps_vel_innov_gate, 1.0f);
}
} else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)10e6)) {
_control_status.flags.gps = false;
ECL_WARN("EKF GPS data stopped");
} else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)1e6) && (_control_status.flags.opt_flow || _control_status.flags.ev_pos)) {
// Handle the case where we are fusing another position source along GPS,
// stop waiting for GPS after 1 s of lost signal
_control_status.flags.gps = false;
ECL_WARN("EKF GPS data stopped, using only EV or OF");
}
}
void Ekf::controlHeightSensorTimeouts()
{
/*
* Handle the case where we have not fused height measurements recently and
* uncertainty exceeds the max allowable. Reset using the best available height
* measurement source, continue using it after the reset and declare the current
* source failed if we have switched.
*/
// Check for IMU accelerometer vibration induced clipping as evidenced by the vertical innovations being positive and not stale.
// Clipping causes the average accel reading to move towards zero which makes the INS think it is falling and produces positive vertical innovations
float var_product_lim = sq(_params.vert_innov_test_lim) * sq(_params.vert_innov_test_lim);
bool bad_vert_accel = (_control_status.flags.baro_hgt && // we can only run this check if vertical position and velocity observations are independent
(sq(_vel_pos_innov[5] * _vel_pos_innov[2]) > var_product_lim * (_vel_pos_innov_var[5] * _vel_pos_innov_var[2])) && // vertical position and velocity sensors are in agreement that we have a significant error
(_vel_pos_innov[2] > 0.0f) && // positive innovation indicates that the inertial nav thinks it is falling
((_imu_sample_delayed.time_us - _baro_sample_delayed.time_us) < 2 * BARO_MAX_INTERVAL) && // vertical position data is fresh
((_imu_sample_delayed.time_us - _gps_sample_delayed.time_us) < 2 * GPS_MAX_INTERVAL)); // vertical velocity data is fresh
// record time of last bad vert accel
if (bad_vert_accel) {
_time_bad_vert_accel = _time_last_imu;
} else {
_time_good_vert_accel = _time_last_imu;
}
// declare a bad vertical acceleration measurement and make the declaration persist
// for a minimum of 10 seconds
if (_bad_vert_accel_detected) {
_bad_vert_accel_detected = (_time_last_imu - _time_bad_vert_accel < BADACC_PROBATION);
} else {
_bad_vert_accel_detected = bad_vert_accel;
}
// check if height is continuously failing because of accel errors
bool continuous_bad_accel_hgt = ((_time_last_imu - _time_good_vert_accel) > (unsigned)_params.bad_acc_reset_delay_us);
// check if height has been inertial deadreckoning for too long
bool hgt_fusion_timeout = ((_time_last_imu - _time_last_hgt_fuse) > (uint64_t)5e6);
// reset the vertical position and velocity states
if (hgt_fusion_timeout || continuous_bad_accel_hgt) {
// boolean that indicates we will do a height reset
bool reset_height = false;
// handle the case where we are using baro for height
if (_control_status.flags.baro_hgt) {
// check if GPS height is available
const gpsSample &gps_init = _gps_buffer.get_newest();
bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);
const baroSample &baro_init = _baro_buffer.get_newest();
bool baro_hgt_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
// check for inertial sensing errors in the last 10 seconds
bool prev_bad_vert_accel = (_time_last_imu - _time_bad_vert_accel < BADACC_PROBATION);
// reset to GPS if adequate GPS data is available and the timeout cannot be blamed on IMU data
bool reset_to_gps = !_gps_hgt_intermittent && gps_hgt_accurate && !prev_bad_vert_accel;
// reset to GPS if GPS data is available and there is no Baro data
reset_to_gps = reset_to_gps || (!_gps_hgt_intermittent && !baro_hgt_available);
// reset to Baro if we are not doing a GPS reset and baro data is available
bool reset_to_baro = !reset_to_gps && baro_hgt_available;
if (reset_to_gps) {
// set height sensor health
_baro_hgt_faulty = true;
// reset the height mode
setControlGPSHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF baro hgt timeout - reset to GPS");
} else if (reset_to_baro) {
// set height sensor health
_baro_hgt_faulty = false;
// reset the height mode
setControlBaroHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF baro hgt timeout - reset to baro");
} else {
// we have nothing we can reset to
// deny a reset
reset_height = false;
}
}
// handle the case we are using GPS for height
if (_control_status.flags.gps_hgt) {
// check if GPS height is available
const gpsSample &gps_init = _gps_buffer.get_newest();
bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);
// check the baro height source for consistency and freshness
const baroSample &baro_init = _baro_buffer.get_newest();
bool baro_data_fresh = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
float baro_innov = _state.pos(2) - (_hgt_sensor_offset - baro_init.hgt + _baro_hgt_offset);
bool baro_data_consistent = fabsf(baro_innov) < (sq(_params.baro_noise) + P[9][9]) * sq(_params.baro_innov_gate);
// if baro data is acceptable and GPS data is inaccurate, reset height to baro
bool reset_to_baro = baro_data_consistent && baro_data_fresh && !_baro_hgt_faulty && !gps_hgt_accurate;
// if GPS height is unavailable and baro data is available, reset height to baro
reset_to_baro = reset_to_baro || (_gps_hgt_intermittent && baro_data_fresh);
// if we cannot switch to baro and GPS data is available, reset height to GPS
bool reset_to_gps = !reset_to_baro && !_gps_hgt_intermittent;
if (reset_to_baro) {
// set height sensor health
_baro_hgt_faulty = false;
// reset the height mode
setControlBaroHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF gps hgt timeout - reset to baro");
} else if (reset_to_gps) {
// reset the height mode
setControlGPSHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF gps hgt timeout - reset to GPS");
} else {
// we have nothing to reset to
reset_height = false;
}
}
// handle the case we are using range finder for height
if (_control_status.flags.rng_hgt) {
// check if range finder data is available
const rangeSample &rng_init = _range_buffer.get_newest();
bool rng_data_available = ((_time_last_imu - rng_init.time_us) < 2 * RNG_MAX_INTERVAL);
// check if baro data is available
const baroSample &baro_init = _baro_buffer.get_newest();
bool baro_data_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
// reset to baro if we have no range data and baro data is available
bool reset_to_baro = !rng_data_available && baro_data_available;
// reset to range data if it is available
bool reset_to_rng = rng_data_available;
if (reset_to_baro) {
// set height sensor health
_rng_hgt_faulty = true;
_baro_hgt_faulty = false;
// reset the height mode
setControlBaroHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF rng hgt timeout - reset to baro");
} else if (reset_to_rng) {
// set height sensor health
_rng_hgt_faulty = false;
// reset the height mode
setControlRangeHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF rng hgt timeout - reset to rng hgt");
} else {
// we have nothing to reset to
reset_height = false;
}
}
// handle the case where we are using external vision data for height
if (_control_status.flags.ev_hgt) {
// check if vision data is available
const extVisionSample &ev_init = _ext_vision_buffer.get_newest();
bool ev_data_available = ((_time_last_imu - ev_init.time_us) < 2 * EV_MAX_INTERVAL);
// check if baro data is available
const baroSample &baro_init = _baro_buffer.get_newest();
bool baro_data_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
// reset to baro if we have no vision data and baro data is available
bool reset_to_baro = !ev_data_available && baro_data_available;
// reset to ev data if it is available
bool reset_to_ev = ev_data_available;
if (reset_to_baro) {
// set height sensor health
_baro_hgt_faulty = false;
// reset the height mode
setControlBaroHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF ev hgt timeout - reset to baro");
} else if (reset_to_ev) {
// reset the height mode
setControlEVHeight();
// request a reset
reset_height = true;
ECL_WARN("EKF ev hgt timeout - reset to ev hgt");
} else {
// we have nothing to reset to
reset_height = false;
}
}
// Reset vertical position and velocity states to the last measurement
if (reset_height) {
resetHeight();
// Reset the timout timer
_time_last_hgt_fuse = _time_last_imu;
}
}
}
void Ekf::controlHeightFusion()
{
// set control flags for the desired primary height source
rangeAidConditionsMet();
_range_aid_mode_selected = (_params.range_aid == 1) && _range_aid_mode_enabled;
if (_params.vdist_sensor_type == VDIST_SENSOR_BARO) {
if (_range_aid_mode_selected && _range_data_ready && !_rng_hgt_faulty) {
setControlRangeHeight();
_fuse_height = true;
// we have just switched to using range finder, calculate height sensor offset such that current
// measurement matches our current height estimate
if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
if (get_terrain_valid()) {
_hgt_sensor_offset = _terrain_vpos;
} else {
_hgt_sensor_offset = _R_rng_to_earth_2_2 * _range_sample_delayed.rng + _state.pos(2);
}
}
} else if (!_range_aid_mode_selected && _baro_data_ready && !_baro_hgt_faulty) {
setControlBaroHeight();
_fuse_height = true;
// we have just switched to using baro height, we don't need to set a height sensor offset
// since we track a separate _baro_hgt_offset
if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
_hgt_sensor_offset = 0.0f;
}
// Turn off ground effect compensation if it times out
if (_control_status.flags.gnd_effect) {
if ((_time_last_imu - _time_last_gnd_effect_on > GNDEFFECT_TIMEOUT)) {
_control_status.flags.gnd_effect = false;
}
}
} else if (_control_status.flags.gps_hgt && _gps_data_ready && !_gps_hgt_intermittent) {
// switch to gps if there was a reset to gps
_fuse_height = true;
// we have just switched to using gps height, calculate height sensor offset such that current
// measurement matches our current height estimate
if (_control_status_prev.flags.gps_hgt != _control_status.flags.gps_hgt) {
_hgt_sensor_offset = _gps_sample_delayed.hgt - _gps_alt_ref + _state.pos(2);
}
}
}
// set the height data source to range if requested
if ((_params.vdist_sensor_type == VDIST_SENSOR_RANGE) && !_rng_hgt_faulty) {
setControlRangeHeight();
_fuse_height = _range_data_ready;
// we have just switched to using range finder, calculate height sensor offset such that current
// measurement matches our current height estimate
if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
// use the parameter rng_gnd_clearance if on ground to avoid a noisy offset initialization (e.g. sonar)
if (_control_status.flags.in_air && get_terrain_valid()) {
_hgt_sensor_offset = _terrain_vpos;
} else if (_control_status.flags.in_air) {
_hgt_sensor_offset = _R_rng_to_earth_2_2 * _range_sample_delayed.rng + _state.pos(2);
} else {
_hgt_sensor_offset = _params.rng_gnd_clearance;
}
}
} else if ((_params.vdist_sensor_type == VDIST_SENSOR_RANGE) && _baro_data_ready && !_baro_hgt_faulty) {
setControlBaroHeight();
_fuse_height = true;
// we have just switched to using baro height, we don't need to set a height sensor offset
// since we track a separate _baro_hgt_offset
if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
_hgt_sensor_offset = 0.0f;
}
}
// Determine if GPS should be used as the height source
if (_params.vdist_sensor_type == VDIST_SENSOR_GPS) {
if (_range_aid_mode_selected && _range_data_ready && !_rng_hgt_faulty) {
setControlRangeHeight();
_fuse_height = true;
// we have just switched to using range finder, calculate height sensor offset such that current
// measurement matches our current height estimate
if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
if (get_terrain_valid()) {
_hgt_sensor_offset = _terrain_vpos;
} else {
_hgt_sensor_offset = _R_rng_to_earth_2_2 * _range_sample_delayed.rng + _state.pos(2);
}
}
} else if (!_range_aid_mode_selected && _gps_data_ready && !_gps_hgt_intermittent && _gps_checks_passed) {
setControlGPSHeight();
_fuse_height = true;
// we have just switched to using gps height, calculate height sensor offset such that current
// measurement matches our current height estimate
if (_control_status_prev.flags.gps_hgt != _control_status.flags.gps_hgt) {
_hgt_sensor_offset = _gps_sample_delayed.hgt - _gps_alt_ref + _state.pos(2);
}
} else if (_control_status.flags.baro_hgt && _baro_data_ready && !_baro_hgt_faulty) {
// switch to baro if there was a reset to baro
_fuse_height = true;
// we have just switched to using baro height, we don't need to set a height sensor offset
// since we track a separate _baro_hgt_offset
if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
_hgt_sensor_offset = 0.0f;
}
}
}
// Determine if we rely on EV height but switched to baro
if (_params.vdist_sensor_type == VDIST_SENSOR_EV) {
if (_control_status.flags.baro_hgt && _baro_data_ready && !_baro_hgt_faulty) {
// switch to baro if there was a reset to baro
_fuse_height = true;
// we have just switched to using baro height, we don't need to set a height sensor offset
// since we track a separate _baro_hgt_offset
if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
_hgt_sensor_offset = 0.0f;
}
}
}
// calculate a filtered offset between the baro origin and local NED origin if we are not using the baro as a height reference
if (!_control_status.flags.baro_hgt && _baro_data_ready) {
float local_time_step = 1e-6f * _delta_time_baro_us;
local_time_step = math::constrain(local_time_step, 0.0f, 1.0f);
// apply a 10 second first order low pass filter to baro offset
float offset_rate_correction = 0.1f * (_baro_sample_delayed.hgt + _state.pos(
2) - _baro_hgt_offset);
_baro_hgt_offset += local_time_step * math::constrain(offset_rate_correction, -0.1f, 0.1f);
}
if ((_time_last_imu - _time_last_hgt_fuse) > 2 * RNG_MAX_INTERVAL && _control_status.flags.rng_hgt
&& (!_range_data_ready || _rng_hgt_faulty)) {
// If we are supposed to be using range finder data as the primary height sensor, have missed or rejected measurements
// and are on the ground, then synthesise a measurement at the expected on ground value
if (!_control_status.flags.in_air) {
_range_sample_delayed.rng = _params.rng_gnd_clearance;
_range_sample_delayed.time_us = _imu_sample_delayed.time_us;
}
_fuse_height = true;
}
}
void Ekf::rangeAidConditionsMet()
{
// if the parameter for range aid is enabled we allow to switch from using the primary height source to using range finder as height source
// under the following conditions
// 1) Vehicle is in-air
// 2) Range data is valid
// 3) Vehicle is no further than max_hagl_for_range_aid away from the ground
// 4) Ground speed is not higher than max_vel_for_range_aid
// 5) Terrain estimate is stable (needs better checks)
if (_control_status.flags.in_air && !_rng_hgt_faulty) {
// check if we can use range finder measurements to estimate height, use hysteresis to avoid rapid switching
bool can_use_range_finder;
if (_range_aid_mode_enabled) {
can_use_range_finder = (_terrain_vpos - _state.pos(2) < _params.max_hagl_for_range_aid) && get_terrain_valid();
} else {
// if we were not using range aid in the previous iteration then require the current height above terrain to be
// smaller than 70 % of the maximum allowed ground distance for range aid
can_use_range_finder = (_terrain_vpos - _state.pos(2) < 0.7f * _params.max_hagl_for_range_aid) && get_terrain_valid();
}
bool horz_vel_valid = (_control_status.flags.gps || _control_status.flags.ev_pos || _control_status.flags.opt_flow)
&& (_fault_status.value == 0);
if (horz_vel_valid) {
float ground_vel = sqrtf(_state.vel(0) * _state.vel(0) + _state.vel(1) * _state.vel(1));
if (_range_aid_mode_enabled) {
can_use_range_finder &= ground_vel < _params.max_vel_for_range_aid;
} else {
// if we were not using range aid in the previous iteration then require the ground velocity to be
// smaller than 70 % of the maximum allowed ground velocity for range aid
can_use_range_finder &= ground_vel < 0.7f * _params.max_vel_for_range_aid;
}
} else {
can_use_range_finder = false;
}
// use hysteresis to check for hagl
if (_range_aid_mode_enabled) {
can_use_range_finder &= ((_hagl_innov * _hagl_innov / (sq(_params.range_aid_innov_gate) * _hagl_innov_var)) < 1.0f);
} else {
// if we were not using range aid in the previous iteration then use a much lower (1/100) threshold to avoid
// switching to range finder too soon (wait for terrain to update).
can_use_range_finder &= ((_hagl_innov * _hagl_innov / (sq(_params.range_aid_innov_gate) * _hagl_innov_var)) < 0.01f);
}
_range_aid_mode_enabled = can_use_range_finder;
} else {
_range_aid_mode_enabled = false;
}
}
void Ekf::checkRangeDataValidity()
{
// check if out of date
if ((_imu_sample_delayed.time_us - _range_sample_delayed .time_us) > 2 * RNG_MAX_INTERVAL) {
_rng_hgt_faulty = true;
return;
}
// Don't allow faulty flag to clear unless range data is continuous
if (_rng_hgt_faulty && !_range_data_continuous) {
return;
}
// Don't run the checks after this unless we have retrieved new data from the buffer
if (!_range_data_ready) {
return;
} else {
// reset fault status when we get new data
_rng_hgt_faulty = (_range_sample_delayed.quality == 0);
}
// Check if excessively tilted
if (_R_rng_to_earth_2_2 < _params.range_cos_max_tilt) {
_rng_hgt_faulty = true;
return;
}
// Check if out of range
if ((_range_sample_delayed.rng > _rng_valid_max_val)
|| (_range_sample_delayed.rng < _rng_valid_min_val)) {
if (_control_status.flags.in_air) {
_rng_hgt_faulty = true;
return;
} else {
// Range finders can fail to provide valid readings when resting on the ground
// or being handled by the user, which prevents use of as a primary height sensor.
// To work around this issue, we replace out of range data with the expected on ground value.
_range_sample_delayed.rng = _params.rng_gnd_clearance;
return;
}
}
// Check for "stuck" range finder measurements when range was not valid for certain period
// This handles a failure mode observed with some lidar sensors
if (((_range_sample_delayed.time_us - _time_last_rng_ready) > (uint64_t)10e6) &&
_control_status.flags.in_air) {
// require a variance of rangefinder values to check for "stuck" measurements
if (_rng_stuck_max_val - _rng_stuck_min_val > _params.range_stuck_threshold) {
_time_last_rng_ready = _range_sample_delayed.time_us;
_rng_stuck_min_val = 0.0f;
_rng_stuck_max_val = 0.0f;
_control_status.flags.rng_stuck = false;
} else {
if (_range_sample_delayed.rng > _rng_stuck_max_val) {
_rng_stuck_max_val = _range_sample_delayed.rng;
}
if (_rng_stuck_min_val < 0.1f || _range_sample_delayed.rng < _rng_stuck_min_val) {
_rng_stuck_min_val = _range_sample_delayed.rng;
}
_control_status.flags.rng_stuck = true;
_rng_hgt_faulty = true;
}
} else {
_time_last_rng_ready = _range_sample_delayed.time_us;
}
}
void Ekf::controlAirDataFusion()
{
// control activation and initialisation/reset of wind states required for airspeed fusion
// If both airspeed and sideslip fusion have timed out and we are not using a drag observation model then we no longer have valid wind estimates
bool airspeed_timed_out = ((_time_last_imu - _time_last_arsp_fuse) > (uint64_t)10e6);
bool sideslip_timed_out = ((_time_last_imu - _time_last_beta_fuse) > (uint64_t)10e6);
if (_control_status.flags.wind && airspeed_timed_out && sideslip_timed_out && !(_params.fusion_mode & MASK_USE_DRAG)) {
_control_status.flags.wind = false;
}
if (_control_status.flags.fuse_aspd && airspeed_timed_out) {
_control_status.flags.fuse_aspd = false;
}
// Always try to fuse airspeed data if available and we are in flight
if (_tas_data_ready && _control_status.flags.in_air) {
// always fuse airsped data if we are flying and data is present
if (!_control_status.flags.fuse_aspd) {
_control_status.flags.fuse_aspd = true;
}
// If starting wind state estimation, reset the wind states and covariances before fusing any data
if (!_control_status.flags.wind) {
// activate the wind states
_control_status.flags.wind = true;
// reset the timout timer to prevent repeated resets
_time_last_arsp_fuse = _time_last_imu;
_time_last_beta_fuse = _time_last_imu;
// reset the wind speed states and corresponding covariances
resetWindStates();
resetWindCovariance();
}
fuseAirspeed();
}
}
void Ekf::controlBetaFusion()
{
// control activation and initialisation/reset of wind states required for synthetic sideslip fusion fusion
// If both airspeed and sideslip fusion have timed out and we are not using a drag observation model then we no longer have valid wind estimates
bool sideslip_timed_out = ((_time_last_imu - _time_last_beta_fuse) > (uint64_t)10e6);
bool airspeed_timed_out = ((_time_last_imu - _time_last_arsp_fuse) > (uint64_t)10e6);
if (_control_status.flags.wind && airspeed_timed_out && sideslip_timed_out && !(_params.fusion_mode & MASK_USE_DRAG)) {
_control_status.flags.wind = false;
}
// Perform synthetic sideslip fusion when in-air and sideslip fuson had been enabled externally in addition to the following criteria:
// Sufficient time has lapsed sice the last fusion
bool beta_fusion_time_triggered = ((_time_last_imu - _time_last_beta_fuse) > _params.beta_avg_ft_us);
if (beta_fusion_time_triggered && _control_status.flags.fuse_beta && _control_status.flags.in_air) {
// If starting wind state estimation, reset the wind states and covariances before fusing any data
if (!_control_status.flags.wind) {
// activate the wind states
_control_status.flags.wind = true;
// reset the timeout timers to prevent repeated resets
_time_last_beta_fuse = _time_last_imu;
_time_last_arsp_fuse = _time_last_imu;
// reset the wind speed states and corresponding covariances
resetWindStates();
resetWindCovariance();
}
fuseSideslip();
}
}
void Ekf::controlDragFusion()
{
if (_params.fusion_mode & MASK_USE_DRAG) {
if (_control_status.flags.in_air
&& !_mag_inhibit_yaw_reset_req) {
if (!_control_status.flags.wind) {
// reset the wind states and covariances when starting drag accel fusion
_control_status.flags.wind = true;
resetWindStates();
resetWindCovariance();
} else if (_drag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_drag_sample_delayed)) {
fuseDrag();
}
} else {
_control_status.flags.wind = false;
}
}
}
void Ekf::controlMagFusion()
{
if (_params.mag_fusion_type >= MAG_FUSE_TYPE_NONE) {
// do not use the magnetometer and deactivate magnetic field states
// save covariance data for re-use if currently doing 3-axis fusion
if (_control_status.flags.mag_3D) {
save_mag_cov_data();
_control_status.flags.mag_3D = false;
}
zeroRows(P, 16, 21);
zeroCols(P, 16, 21);
_mag_decl_cov_reset = false;
_control_status.flags.mag_hdg = false;
return;
}
// If we are on ground, store the local position and time to use as a reference
// Also reset the flight alignment flag so that the mag fields will be re-initialised next time we achieve flight altitude
if (!_control_status.flags.in_air) {
_last_on_ground_posD = _state.pos(2);
_control_status.flags.mag_align_complete = false;
_num_bad_flight_yaw_events = 0;
}
// check for new magnetometer data that has fallen behind the fusion time horizon
// If we are using external vision data for heading then no magnetometer fusion is used
if (!_control_status.flags.ev_yaw && !_control_status.flags.gps_yaw && _mag_data_ready) {
// We need to reset the yaw angle after climbing away from the ground to enable
// recovery from ground level magnetic interference.
if (!_control_status.flags.mag_align_complete && _control_status.flags.in_air) {
// Check if height has increased sufficiently to be away from ground magnetic anomalies
// and request a yaw reset if not already requested.
float terrain_vpos_estimate = get_terrain_valid() ? _terrain_vpos : _last_on_ground_posD;
_mag_yaw_reset_req |= (terrain_vpos_estimate - _state.pos(2)) > 1.5f;
}
// perform a yaw reset if requested by other functions
if (_mag_yaw_reset_req && _control_status.flags.tilt_align) {
if (!_mag_use_inhibit ) {
if (!_control_status.flags.mag_align_complete && _control_status.flags.fixed_wing && _control_status.flags.in_air) {
// A fixed wing vehicle can use GPS to bound yaw errors immediately after launch
_control_status.flags.mag_align_complete = realignYawGPS();
if (_velpos_reset_request) {
resetVelocity();
resetPosition();
_velpos_reset_request = false;
}
} else {
_control_status.flags.mag_align_complete = resetMagHeading(_mag_sample_delayed.mag) && _control_status.flags.in_air;
}
}
_control_status.flags.yaw_align = _control_status.flags.yaw_align || _control_status.flags.mag_align_complete;
_mag_yaw_reset_req = false;
}
// Determine if we should use simple magnetic heading fusion which works better when there are large external disturbances
// or the more accurate 3-axis fusion
if (_control_status.flags.mag_fault) {
// do no magnetometer fusion at all
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_3D = false;
} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_AUTO || _params.mag_fusion_type == MAG_FUSE_TYPE_AUTOFW) {
// Check if there has been enough change in horizontal velocity to make yaw observable
// Apply hysteresis to check to avoid rapid toggling
if (_yaw_angle_observable) {
_yaw_angle_observable = _accel_lpf_NE.norm() > _params.mag_acc_gate;
} else {
_yaw_angle_observable = _accel_lpf_NE.norm() > 2.0f * _params.mag_acc_gate;
}
_yaw_angle_observable = _yaw_angle_observable && (_control_status.flags.gps || _control_status.flags.ev_pos);
// check if there is enough yaw rotation to make the mag bias states observable
if (!_mag_bias_observable && (fabsf(_yaw_rate_lpf_ef) > _params.mag_yaw_rate_gate)) {
// initial yaw motion is detected
_mag_bias_observable = true;
_yaw_delta_ef = 0.0f;
_time_yaw_started = _imu_sample_delayed.time_us;
} else if (_mag_bias_observable) {
// monitor yaw rotation in 45 deg sections.
// a rotation of 45 deg is sufficient to make the mag bias observable
if (fabsf(_yaw_delta_ef) > math::radians(45.0f)) {
_time_yaw_started = _imu_sample_delayed.time_us;
_yaw_delta_ef = 0.0f;
}
// require sustained yaw motion of 50% the initial yaw rate threshold
float min_yaw_change_req = 0.5f * _params.mag_yaw_rate_gate * (1e-6f * (float)(_imu_sample_delayed.time_us - _time_yaw_started));
_mag_bias_observable = fabsf(_yaw_delta_ef) > min_yaw_change_req;
} else {
_mag_bias_observable = false;
}
// record the last time that movement was suitable for use of 3-axis magnetometer fusion
if (_mag_bias_observable || _yaw_angle_observable) {
_time_last_movement = _imu_sample_delayed.time_us;
}
// decide whether 3-axis magnetometer fusion can be used
bool use_3D_fusion = _control_status.flags.tilt_align && // Use of 3D fusion requires valid tilt estimates
_control_status.flags.in_air && // don't use when on the ground because of magnetic anomalies
_control_status.flags.mag_align_complete &&
((_imu_sample_delayed.time_us - _time_last_movement) < 2 * 1000 * 1000); // Using 3-axis fusion for a minimum period after to allow for false negatives
// perform switch-over
if (use_3D_fusion) {
if (!_control_status.flags.mag_3D) {
// reset the mag field covariances
zeroRows(P, 16, 21);
zeroCols(P, 16, 21);
// re-instate variances for the D earth axis and XYZ body axis field
for (uint8_t index = 0; index <= 3; index ++) {
P[index + 18][index + 18] = _saved_mag_bf_variance[index];
}
// re-instate the NE axis covariance sub-matrix
for (uint8_t row = 0; row <= 1; row ++) {
for (uint8_t col = 0; col <= 1; col ++) {
P[row + 16][col + 16] = _saved_mag_ef_covmat[row][col];
}
}
}
// only use one type of mag fusion at the same time
_control_status.flags.mag_3D = _control_status.flags.mag_align_complete;
_control_status.flags.mag_hdg = !_control_status.flags.mag_3D;
} else {
// save covariance data for re-use if currently doing 3-axis fusion
if (_control_status.flags.mag_3D) {
save_mag_cov_data();
_control_status.flags.mag_3D = false;
}
_control_status.flags.mag_hdg = true;
}
/*
Control switch-over between only updating the mag states to updating all states
When flying as a fixed wing aircraft, a misaligned magnetometer can cause an error in pitch/roll and accel bias estimates.
When MAG_FUSE_TYPE_AUTOFW is selected and the vehicle is flying as a fixed wing, then magnetometer fusion is only allowed
to access the magnetic field states.
*/
_control_status.flags.update_mag_states_only = (_params.mag_fusion_type == MAG_FUSE_TYPE_AUTOFW)
&& _control_status.flags.fixed_wing;
// For the first 5 seconds after switching to 3-axis fusion we allow the magnetic field state estimates to stabilise
// before they are used to constrain heading drift
_flt_mag_align_converging = ((_imu_sample_delayed.time_us - _flt_mag_align_start_time) < (uint64_t)5e6);
if (_control_status.flags.mag_3D && _control_status_prev.flags.update_mag_states_only && !_control_status.flags.update_mag_states_only) {
// When re-commencing use of magnetometer to correct vehicle states
// set the field state variance to the observation variance and zero
// the covariance terms to allow the field states re-learn rapidly
zeroRows(P, 16, 21);
zeroCols(P, 16, 21);
_mag_decl_cov_reset = false;
for (uint8_t index = 0; index <= 5; index ++) {
P[index + 16][index + 16] = sq(_params.mag_noise);
}
// save covariance data for re-use when auto-switching between heading and 3-axis fusion
save_mag_cov_data();
}
} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_HEADING) {
// always use heading fusion
_control_status.flags.mag_hdg = true;
// save covariance data for re-use if currently doing 3-axis fusion
if (_control_status.flags.mag_3D) {
save_mag_cov_data();
_control_status.flags.mag_3D = false;
}
} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_3D) {
if (!_control_status.flags.mag_3D && _control_status.flags.yaw_align) {
// only commence 3-axis fusion when yaw is aligned and field states set
_control_status.flags.mag_3D = true;
}
} else {
// do no magnetometer fusion at all
_control_status.flags.mag_hdg = false;
// save covariance data for re-use if currently doing 3-axis fusion
if (_control_status.flags.mag_3D) {
save_mag_cov_data();
_control_status.flags.mag_3D = false;
}
}
// if we are using 3-axis magnetometer fusion, but without external aiding, then the declination must be fused as an observation to prevent long term heading drift
// fusing declination when gps aiding is available is optional, but recommended to prevent problem if the vehicle is static for extended periods of time
if (_control_status.flags.mag_3D && (!_control_status.flags.gps || (_params.mag_declination_source & MASK_FUSE_DECL))) {
_control_status.flags.mag_dec = true;
} else {
_control_status.flags.mag_dec = false;
}
// If the user has selected auto protection against indoor magnetic field errors, only use the magnetometer
// if a yaw angle relative to true North is required for navigation. If no GPS or other earth frame aiding
// is available, assume that we are operating indoors and the magnetometer should not be used.
bool user_selected = (_params.mag_fusion_type == MAG_FUSE_TYPE_INDOOR);
bool not_using_gps = !(_params.fusion_mode & MASK_USE_GPS) || !_control_status.flags.gps;
bool not_using_evpos = !(_params.fusion_mode & MASK_USE_EVPOS) || !_control_status.flags.ev_pos;
bool not_selected_evyaw = !(_params.fusion_mode & MASK_USE_EVYAW);
if (user_selected && not_using_gps && not_using_evpos && not_selected_evyaw) {
_mag_use_inhibit = true;
} else {
_mag_use_inhibit = false;
_mag_use_not_inhibit_us = _imu_sample_delayed.time_us;
}
// If magnetometer use has been inhibited continuously then a yaw reset is required for a valid heading
if (uint32_t(_imu_sample_delayed.time_us - _mag_use_not_inhibit_us) > (uint32_t)5e6) {
_mag_inhibit_yaw_reset_req = true;
}
// fuse magnetometer data using the selected methods
if (_control_status.flags.mag_3D && _control_status.flags.yaw_align) {
if (!_mag_decl_cov_reset) {
// After any magnetic field covariance reset event the earth field state
// covariances need to be corrected to incorporate knowedge of the declination
// before fusing magnetomer data to prevent rapid rotation of the earth field
// states for the first few observations.
fuseDeclination(0.02f);
_mag_decl_cov_reset = true;
fuseMag();
} else {
// The normal sequence is to fuse the magnetometer data first before fusing
// declination angle at a higher uncertainty to allow some learning of
// declination angle over time.
fuseMag();
if (_control_status.flags.mag_dec) {
fuseDeclination(0.5f);
}
}
} else if (_control_status.flags.mag_hdg && _control_status.flags.yaw_align) {
// fusion of an Euler yaw angle from either a 321 or 312 rotation sequence
fuseHeading();
} else {
// do no fusion at all
}
}
}
void Ekf::controlVelPosFusion()
{
// if we aren't doing any aiding, fake GPS measurements at the last known position to constrain drift
// Coincide fake measurements with baro data for efficiency with a minimum fusion rate of 5Hz
if (!(_params.fusion_mode & MASK_USE_GPS)) {
_control_status.flags.gps = false;
}
if (!_control_status.flags.gps &&
!_control_status.flags.opt_flow &&
!_control_status.flags.ev_pos &&
!_control_status.flags.ev_vel &&
!(_control_status.flags.fuse_aspd && _control_status.flags.fuse_beta)) {
// We now need to use a synthetic position observation to prevent unconstrained drift of the INS states.
_using_synthetic_position = true;
// Fuse synthetic position observations every 200msec
if (((_time_last_imu - _time_last_fake_gps) > (uint64_t)2e5) || _fuse_height) {
// Reset position and velocity states if we re-commence this aiding method
if ((_time_last_imu - _time_last_fake_gps) > (uint64_t)4e5) {
resetPosition();
resetVelocity();
_fuse_hpos_as_odom = false;
if (_time_last_fake_gps != 0) {
ECL_WARN("EKF stopping navigation");
}
}
_fuse_pos = true;
_fuse_hor_vel = false;
_fuse_vert_vel = false;
_time_last_fake_gps = _time_last_imu;
if (_control_status.flags.in_air && _control_status.flags.tilt_align) {
_posObsNoiseNE = fmaxf(_params.pos_noaid_noise, _params.gps_pos_noise);
} else {
_posObsNoiseNE = 0.5f;
}
_vel_pos_innov[0] = 0.0f;
_vel_pos_innov[1] = 0.0f;
_vel_pos_innov[2] = 0.0f;
_vel_pos_innov[3] = _state.pos(0) - _last_known_posNE(0);
_vel_pos_innov[4] = _state.pos(1) - _last_known_posNE(1);
// glitch protection is not required so set gate to a large value
_posInnovGateNE = 100.0f;
}
} else {
_using_synthetic_position = false;
}
// Fuse available NED velocity and position data into the main filter
if (_fuse_height || _fuse_pos || _fuse_hor_vel || _fuse_vert_vel) {
fuseVelPosHeight();
}
}
void Ekf::controlAuxVelFusion()
{
bool data_ready = _auxvel_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_auxvel_sample_delayed);
bool primary_aiding = _control_status.flags.gps || _control_status.flags.ev_pos || _control_status.flags.opt_flow;
if (data_ready && primary_aiding) {
_fuse_hor_vel = _fuse_vert_vel = _fuse_pos = _fuse_height = false;
_fuse_hor_vel_aux = true;
_aux_vel_innov[0] = _state.vel(0) - _auxvel_sample_delayed.velNE(0);
_aux_vel_innov[1] = _state.vel(1) - _auxvel_sample_delayed.velNE(1);
_velObsVarNED(0) = _auxvel_sample_delayed.velVarNE(0);
_velObsVarNED(1) = _auxvel_sample_delayed.velVarNE(1);
_hvelInnovGate = _params.auxvel_gate;
fuseVelPosHeight();
}
}