void Ekf::controlOpticalFlowFusion()
{
// Check for new optical flow data that has fallen behind the fusion time horizon
if (_flow_data_ready) {
// 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
&& (_time_last_imu - _time_last_hagl_fuse) < 5e5) // 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, 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 then the velocity and position states and covariances need to be set
if (!_control_status.flags.gps) {
// constrain height above ground to be above minimum possible
float heightAboveGndEst = fmaxf((_terrain_vpos - _state.pos(2)), _params.rng_gnd_clearance);
// calculate absolute distance from focal point to centre of frame assuming a flat earth
float range = heightAboveGndEst / _R_to_earth(2, 2);
if ((range - _params.rng_gnd_clearance) > 0.3f && _flow_sample_delayed.dt > 0.05f) {
// we should have reliable OF measurements so
// calculate X and Y body relative velocities from OF measurements
Vector3f vel_optflow_body;
vel_optflow_body(0) = - range * _flow_sample_delayed.flowRadXYcomp(1) / _flow_sample_delayed.dt;
vel_optflow_body(1) = range * _flow_sample_delayed.flowRadXYcomp(0) / _flow_sample_delayed.dt;
vel_optflow_body(2) = 0.0f;
// rotate from body to earth frame
Vector3f vel_optflow_earth;
vel_optflow_earth = _R_to_earth * vel_optflow_body;
// take x and Y components
_state.vel(0) = vel_optflow_earth(0);
_state.vel(1) = vel_optflow_earth(1);
} else {
_state.vel(0) = 0.0f;
_state.vel(1) = 0.0f;
}
// reset the velocity covariance terms
zeroRows(P,4,5);
zeroCols(P,4,5);
// reset the horizontal velocity variance using the optical flow noise variance
P[5][5] = P[4][4] = sq(range) * calcOptFlowMeasVar();
if (!_control_status.flags.in_air) {
// we are likely starting OF for the first time so reset the horizontal position and vertical velocity states
_state.pos(0) = 0.0f;
_state.pos(1) = 0.0f;
// reset the corresponding covariances
// we are by definition at the origin at commencement so variances are also zeroed
zeroRows(P,7,8);
zeroCols(P,7,8);
// 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 are relying on optical flow fusion and lose it
if (_control_status.flags.opt_flow && !_control_status.flags.gps) {
// We are relying on flow aiding to constrain attitude drift so after 5s without aiding we need to do something
if ((_time_last_imu - _time_last_of_fuse > 5e6)) {
// Switch to the non-aiding mode, zero the velocity states
// and set the synthetic position to the current estimate
_control_status.flags.opt_flow = false;
_last_known_posNE(0) = _state.pos(0);
_last_known_posNE(1) = _state.pos(1);
_state.vel.setZero();
}
}
// fuse the data
if (_control_status.flags.opt_flow) {
// Update optical flow bias estimates
calcOptFlowBias();
// Fuse optical flow LOS rate observations into the main filter
fuseOptFlow();
_last_known_posNE(0) = _state.pos(0);
_last_known_posNE(1) = _state.pos(1);
}
}
}
void Ekf::controlFusionModes()
{
// Determine the vehicle status
calculateVehicleStatus();
// Get the magnetic declination
calcMagDeclination();
// Check for tilt convergence during initial alignment
// filter the tilt error vector using a 1 sec time constant LPF
float filt_coef = 1.0f * _imu_sample_delayed.delta_ang_dt;
_tilt_err_length_filt = filt_coef * _tilt_err_vec.norm() + (1.0f - filt_coef) * _tilt_err_length_filt;
// Once the tilt error has reduced sufficiently, initialise the yaw and magnetic field states
if (_tilt_err_length_filt < 0.005f && !_control_status.flags.tilt_align) {
_control_status.flags.tilt_align = true;
_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
}
// optical flow fusion mode selection logic
// to start using optical flow data we need angular alignment complete, and fresh optical flow and height above terrain data
if ((_params.fusion_mode & MASK_USE_OF) && !_control_status.flags.opt_flow && _control_status.flags.tilt_align
&& (_time_last_imu - _time_last_optflow) < 5e5 && (_time_last_imu - _time_last_hagl_fuse) < 5e5) {
// 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, 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 and are in air, then we need to reset the velocity to be consistent with the optical flow reading
if (!_control_status.flags.gps) {
// calculate the rotation matrix from body to earth frame
matrix::Dcm<float> body_to_earth(_state.quat_nominal);
// constrain height above ground to be above minimum possible
float heightAboveGndEst = fmaxf((_terrain_vpos - _state.pos(2)), _params.rng_gnd_clearance);
// calculate absolute distance from focal point to centre of frame assuming a flat earth
float range = heightAboveGndEst / body_to_earth(2, 2);
if (_in_air && (range - _params.rng_gnd_clearance) > 0.3f && _flow_sample_delayed.dt > 0.05f) {
// calculate X and Y body relative velocities from OF measurements
Vector3f vel_optflow_body;
vel_optflow_body(0) = - range * _flow_sample_delayed.flowRadXYcomp(1) / _flow_sample_delayed.dt;
vel_optflow_body(1) = range * _flow_sample_delayed.flowRadXYcomp(0) / _flow_sample_delayed.dt;
vel_optflow_body(2) = 0.0f;
// rotate from body to earth frame
Vector3f vel_optflow_earth;
vel_optflow_earth = body_to_earth * vel_optflow_body;
// take x and Y components
_state.vel(0) = vel_optflow_earth(0);
_state.vel(1) = vel_optflow_earth(1);
} else {
_state.vel.setZero();
}
}
}
} else if (!(_params.fusion_mode & MASK_USE_OF)) {
_control_status.flags.opt_flow = false;
}
// GPS fusion mode selection logic
// To start use GPS we need angular alignment completed, the local NED origin set and fresh GPS data
if ((_params.fusion_mode & MASK_USE_GPS) && !_control_status.flags.gps) {
if (_control_status.flags.tilt_align && (_time_last_imu - _time_last_gps) < 5e5 && _NED_origin_initialised
&& (_time_last_imu - _last_gps_fail_us > 5e6)) {
// 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 start using gps aiding
if (_control_status.flags.yaw_align) {
_control_status.flags.gps = true;
_time_last_gps = _time_last_imu;
// if we are not already aiding with optical flow, then we need to reset the position and velocity
if (!_control_status.flags.opt_flow) {
_control_status.flags.gps = resetPosition();
_control_status.flags.gps = resetVelocity();
}
}
}
} else if (!(_params.fusion_mode & MASK_USE_GPS)) {
_control_status.flags.gps = false;
}
// handle the case when we are relying on GPS fusion and lose it
if (_control_status.flags.gps && !_control_status.flags.opt_flow) {
// We are relying on GPS aiding to constrain attitude drift so after 10 seconds without aiding we need to do something
if ((_time_last_imu - _time_last_pos_fuse > 10e6) && (_time_last_imu - _time_last_vel_fuse > 10e6)) {
if (_time_last_imu - _time_last_gps > 5e5) {
// if we don't have gps then we need to switch to the non-aiding mode, zero the veloity states
// and set the synthetic GPS position to the current estimate
_control_status.flags.gps = false;
_last_known_posNE(0) = _state.pos(0);
_last_known_posNE(1) = _state.pos(1);
_state.vel.setZero();
} else {
// Reset states to the last GPS measurement
resetPosition();
resetVelocity();
}
}
}
/*
* 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.
*/
if ((P[8][8] > sq(_params.hgt_reset_lim)) && ((_time_last_imu - _time_last_hgt_fuse) > 5e6)) {
// handle the case where we are using baro for height
if (_control_status.flags.baro_hgt) {
// check if GPS height is available
gpsSample gps_init = _gps_buffer.get_newest();
bool gps_hgt_available = ((_time_last_imu - gps_init.time_us) < 2 * GPS_MAX_INTERVAL);
bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);
baroSample baro_init = _baro_buffer.get_newest();
bool baro_hgt_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
// use the gps if it is accurate or there is no baro data available
if (gps_hgt_available && (gps_hgt_accurate || !baro_hgt_available)) {
// declare the baro as unhealthy
_baro_hgt_faulty = true;
// set the height mode to the GPS
_control_status.flags.baro_hgt = false;
_control_status.flags.gps_hgt = true;
_control_status.flags.rng_hgt = false;
// adjust the height offset so we can use the GPS
_hgt_sensor_offset = _state.pos(2) + gps_init.hgt - _gps_alt_ref;
if (!baro_hgt_available) {
printf("EKF baro hgt timeout - switching to gps\n");
}
}
}
// handle the case we are using GPS for height
if (_control_status.flags.gps_hgt) {
// check if GPS height is available
gpsSample gps_init = _gps_buffer.get_newest();
bool gps_hgt_available = ((_time_last_imu - gps_init.time_us) < 2 * GPS_MAX_INTERVAL);
bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);
// check the baro height source for consistency and freshness
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[8][8]) * sq(_params.baro_innov_gate);
// if baro data is consistent and fresh or GPS height is unavailable or inaccurate, we switch to baro for height
if ((baro_data_consistent && baro_data_fresh) || !gps_hgt_available || !gps_hgt_accurate) {
// declare the GPS height unhealthy
_gps_hgt_faulty = true;
// set the height mode to the baro
_control_status.flags.baro_hgt = true;
_control_status.flags.gps_hgt = false;
_control_status.flags.rng_hgt = false;
printf("EKF gps hgt timeout - switching to baro\n");
}
}
// handle the case we are using range finder for height
if (_control_status.flags.rng_hgt) {
// check if range finder data is available
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
baroSample baro_init = _baro_buffer.get_newest();
bool baro_data_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
// check if baro data is consistent
float baro_innov = _state.pos(2) - (_hgt_sensor_offset - baro_init.hgt + _baro_hgt_offset);
bool baro_data_consistent = sq(baro_innov) < (sq(_params.baro_noise) + P[8][8]) * sq(_params.baro_innov_gate);
// switch to baro if necessary or preferable
bool switch_to_baro = (!rng_data_available && baro_data_available) || (baro_data_consistent && baro_data_available);
if (switch_to_baro) {
// declare the range finder height unhealthy
_rng_hgt_faulty = true;
// set the height mode to the baro
_control_status.flags.baro_hgt = true;
_control_status.flags.gps_hgt = false;
_control_status.flags.rng_hgt = false;
printf("EKF rng hgt timeout - switching to baro\n");
}
}
// Reset vertical position and velocity states to the last measurement
resetHeight();
}
// handle the case when we are relying on optical flow fusion and lose it
if (_control_status.flags.opt_flow && !_control_status.flags.gps) {
// We are relying on flow aiding to constrain attitude drift so after 5s without aiding we need to do something
if ((_time_last_imu - _time_last_of_fuse > 5e6)) {
// Switch to the non-aiding mode, zero the veloity states
// and set the synthetic position to the current estimate
_control_status.flags.opt_flow = false;
_last_known_posNE(0) = _state.pos(0);
_last_known_posNE(1) = _state.pos(1);
_state.vel.setZero();
}
}
// 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 (_params.mag_fusion_type == MAG_FUSE_TYPE_AUTO) {
if (!_control_status.flags.armed) {
// use heading fusion for initial startup
_control_status.flags.mag_hdg = true;
_control_status.flags.mag_2D = false;
_control_status.flags.mag_3D = false;
} else {
if (_control_status.flags.in_air) {
// if transitioning into 3-axis fusion mode, we need to initialise the yaw angle and field states
if (!_control_status.flags.mag_3D) {
_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
}
// use 3D mag fusion when airborne
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_2D = false;
_control_status.flags.mag_3D = true;
} else {
// use heading fusion when on the ground
_control_status.flags.mag_hdg = true;
_control_status.flags.mag_2D = false;
_control_status.flags.mag_3D = false;
}
}
} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_HEADING) {
// always use heading fusion
_control_status.flags.mag_hdg = true;
_control_status.flags.mag_2D = false;
_control_status.flags.mag_3D = false;
} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_2D) {
// always use 2D mag fusion
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_2D = true;
_control_status.flags.mag_3D = false;
} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_3D) {
// if transitioning into 3-axis fusion mode, we need to initialise the yaw angle and field states
if (!_control_status.flags.mag_3D) {
_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
}
// always use 3-axis mag fusion
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_2D = false;
_control_status.flags.mag_3D = true;
} else {
// do no magnetometer fusion at all
_control_status.flags.mag_hdg = false;
_control_status.flags.mag_2D = false;
_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 recommneded 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;
}
// Control the soure of height measurements for the main filter
if ((_params.vdist_sensor_type == VDIST_SENSOR_BARO && !_baro_hgt_faulty) || _control_status.flags.baro_hgt) {
_control_status.flags.baro_hgt = true;
_control_status.flags.gps_hgt = false;
_control_status.flags.rng_hgt = false;
} else if ((_params.vdist_sensor_type == VDIST_SENSOR_GPS && !_gps_hgt_faulty) || _control_status.flags.gps_hgt) {
_control_status.flags.baro_hgt = false;
_control_status.flags.gps_hgt = true;
_control_status.flags.rng_hgt = false;
} else if (_params.vdist_sensor_type == VDIST_SENSOR_RANGE && !_rng_hgt_faulty) {
_control_status.flags.baro_hgt = false;
_control_status.flags.gps_hgt = false;
_control_status.flags.rng_hgt = true;
}
// Placeholder for control of wind velocity states estimation
// TODO add methods for true airspeed and/or sidelsip fusion or some type of drag force measurement
if (false) {
_control_status.flags.wind = false;
}
// Store the status to enable change detection
_control_status_prev.value = _control_status.value;
}
