PX4-Autopilot/src/modules/ekf2/EKF/gps_control.cpp

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/**
 * @file gps_control.cpp
 * Control functions for ekf GNSS fusion
 */

#include "ekf.h"
#include <mathlib/mathlib.h>

void Ekf::controlGpsFusion()
{
	if (!(_params.fusion_mode & MASK_USE_GPS)) {
		stopGpsFusion();
		return;
	}

	// Check for new GPS data that has fallen behind the fusion time horizon
	if (_gps_data_ready) {
		const bool gps_checks_passing = isTimedOut(_last_gps_fail_us, (uint64_t)5e6);
		const bool gps_checks_failing = isTimedOut(_last_gps_pass_us, (uint64_t)5e6);

		controlGpsYawFusion(gps_checks_passing, gps_checks_failing);

		// 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
		const bool mandatory_conditions_passing = _control_status.flags.tilt_align
				&& _control_status.flags.yaw_align
				&& _NED_origin_initialised;

		const bool continuing_conditions_passing = mandatory_conditions_passing && !gps_checks_failing;
		const bool starting_conditions_passing = continuing_conditions_passing && gps_checks_passing;

		if (_control_status.flags.gps) {
			if (mandatory_conditions_passing) {
				if (continuing_conditions_passing
				    || !isOtherSourceOfHorizontalAidingThan(_control_status.flags.gps)) {

					fuseGpsVelPos();

					if (shouldResetGpsFusion()) {
						const bool was_gps_signal_lost = isTimedOut(_time_prev_gps_us, 1000000);

						/* A reset is not performed when getting GPS back after a significant period of no data
						 * because the timeout could have been caused by bad GPS.
						 * The total number of resets allowed per boot cycle is limited.
						 */
						if (isYawFailure()
						    && _control_status.flags.in_air
						    && !was_gps_signal_lost
						    && _ekfgsf_yaw_reset_count < _params.EKFGSF_reset_count_limit
						    && isTimedOut(_ekfgsf_yaw_reset_time, 5000000)) {
							// The minimum time interval between resets to the EKF-GSF estimate is limited to allow the EKF-GSF time
							// to improve its estimate if the previous reset was not successful.
							if (resetYawToEKFGSF()) {
								ECL_WARN("GPS emergency yaw reset");
							}

						} else {
							// 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
								_mag_yaw_reset_req = true;
							}

							_warning_events.flags.gps_fusion_timout = true;
							ECL_WARN("GPS fusion timeout - resetting");
						}

						resetVelocityToGps(_gps_sample_delayed);
						resetHorizontalPositionToGps(_gps_sample_delayed);
					}

				} else {
					stopGpsFusion();
					_warning_events.flags.gps_quality_poor = true;
					ECL_WARN("GPS quality poor - stopping use");

					// TODO: move this to EV control logic
					// 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)) {
						resetHorizontalPositionToVision();
					}
				}

			} else { // mandatory conditions are not passing
				stopGpsFusion();
			}

		} else {
			if (starting_conditions_passing) {
				// 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.ev_yaw
				    || _mag_inhibit_yaw_reset_req
				    || _mag_yaw_reset_req) {

					_mag_yaw_reset_req = true;

					// Stop the vision for yaw fusion and do not allow it to start again
					stopEvYawFusion();
					_inhibit_ev_yaw_use = true;

				} else {
					startGpsFusion();
				}

			} else if (gps_checks_passing && !_control_status.flags.yaw_align && (_params.mag_fusion_type == MAG_FUSE_TYPE_NONE)) {
				// If no mag is used, align using the yaw estimator (if available)
				if (resetYawToEKFGSF()) {
					_information_events.flags.yaw_aligned_to_imu_gps = true;
					ECL_INFO("Yaw aligned using IMU and GPS");
					resetVelocityToGps(_gps_sample_delayed);
					resetHorizontalPositionToGps(_gps_sample_delayed);
				}
			}
		}

	} else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)10e6)) {
		stopGpsFusion();
		_warning_events.flags.gps_data_stopped = true;
		ECL_WARN("GPS data stopped");

	}  else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)1e6)
		    && isOtherSourceOfHorizontalAidingThan(_control_status.flags.gps)) {
		// Handle the case where we are fusing another position source along GPS,
		// stop waiting for GPS after 1 s of lost signal
		stopGpsFusion();
		_warning_events.flags.gps_data_stopped_using_alternate = true;
		ECL_WARN("GPS data stopped, using only EV, OF or air data");
	}
}

bool Ekf::shouldResetGpsFusion() const
{
	/* We are relying on aiding to constrain drift so after a specified time
	 * with no aiding we need to do something
	 */
	const bool is_reset_required = hasHorizontalAidingTimedOut()
				       || isTimedOut(_time_last_hor_pos_fuse, 2 * _params.reset_timeout_max);

	/* Logic controlling the reset of navigation filter yaw to the EKF-GSF estimate to recover from loss of
	 * navigation casued by a bad yaw estimate.

	 * A rapid reset to the EKF-GSF estimate is performed after a recent takeoff if horizontal velocity
	 * innovation checks fail. This enables recovery from a bad yaw estimate. After 30 seconds from takeoff,
	 * different test criteria are used that take longer to trigger and reduce false positives. A reset is
	 * not performed if the fault condition was present before flight to prevent triggering due to GPS glitches
	 * or other sensor errors.
	 */
	const bool is_recent_takeoff_nav_failure = _control_status.flags.in_air
			&& isRecent(_time_last_on_ground_us, 30000000)
			&& isTimedOut(_time_last_hor_vel_fuse, _params.EKFGSF_reset_delay)
			&& (_time_last_hor_vel_fuse > _time_last_on_ground_us);

	const bool is_inflight_nav_failure = _control_status.flags.in_air
					     && isTimedOut(_time_last_hor_vel_fuse, _params.reset_timeout_max)
					     && isTimedOut(_time_last_hor_pos_fuse, _params.reset_timeout_max)
					     && (_time_last_hor_vel_fuse > _time_last_on_ground_us)
					     && (_time_last_hor_pos_fuse > _time_last_on_ground_us);

	return (is_reset_required || is_recent_takeoff_nav_failure || is_inflight_nav_failure);
}

bool Ekf::isYawFailure() const
{
	if (!isYawEmergencyEstimateAvailable()) {
		return false;
	}

	const float euler_yaw = getEulerYaw(_R_to_earth);
	const float yaw_error = wrap_pi(euler_yaw - _yawEstimator.getYaw());

	return fabsf(yaw_error) > math::radians(25.f);
}