PX4-Autopilot/src/lib/airspeed_validator/AirspeedValidator.cpp

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/**
 * @file AirspeedValidator.cpp
 * Estimates airspeed scale error (from indicated to calibrated airspeed), performes
 * checks on airspeed measurement input and reports airspeed valid or invalid.
 */

#include "AirspeedValidator.hpp"


void
AirspeedValidator::update_airspeed_validator(const airspeed_validator_update_data &input_data)
{
	// get indicated airspeed from input data (raw airspeed)
	_IAS = input_data.airspeed_indicated_raw;

	// to be able to detect missing data, save timestamp (used in data_missing check)
	if (input_data.airspeed_timestamp != _previous_airspeed_timestamp && input_data.airspeed_timestamp > 0) {
		_time_last_airspeed = input_data.timestamp;
		_previous_airspeed_timestamp = input_data.airspeed_timestamp;
	}

	update_CAS_scale();
	update_CAS_TAS(input_data.air_pressure_pa, input_data.air_temperature_celsius);
	update_wind_estimator(input_data.timestamp, input_data.airspeed_true_raw, input_data.lpos_valid, input_data.lpos_vx,
			      input_data.lpos_vy,
			      input_data.lpos_vz, input_data.lpos_evh, input_data.lpos_evv, input_data.att_q);
	update_in_fixed_wing_flight(input_data.in_fixed_wing_flight);
	check_airspeed_innovation(input_data.timestamp, input_data.vel_test_ratio, input_data.mag_test_ratio);
	check_load_factor(input_data.accel_z);
	update_airspeed_valid_status(input_data.timestamp);
}

void
AirspeedValidator::update_wind_estimator(const uint64_t time_now_usec, float airspeed_true_raw, bool lpos_valid,
		float lpos_vx, float lpos_vy,
		float lpos_vz, float lpos_evh, float lpos_evv, const float att_q[4])
{
	_wind_estimator.update(time_now_usec);

	if (lpos_valid && _in_fixed_wing_flight) {

		Vector3f vI(lpos_vx, lpos_vy, lpos_vz);
		Quatf q(att_q);

		// airspeed fusion (with raw TAS)
		const Vector3f vel_var{Dcmf(q) *Vector3f{lpos_evh, lpos_evh, lpos_evv}};
		_wind_estimator.fuse_airspeed(time_now_usec, airspeed_true_raw, vI, Vector2f{vel_var(0), vel_var(1)});

		// sideslip fusion
		_wind_estimator.fuse_beta(time_now_usec, vI, q);
	}
}

// this function returns the current states of the wind estimator to be published in the airspeed module
wind_estimate_s
AirspeedValidator::get_wind_estimator_states(uint64_t timestamp)
{
	wind_estimate_s wind_est = {};

	wind_est.timestamp = timestamp;
	float wind[2];
	_wind_estimator.get_wind(wind);
	wind_est.windspeed_north = wind[0];
	wind_est.windspeed_east = wind[1];
	float wind_cov[2];
	_wind_estimator.get_wind_var(wind_cov);
	wind_est.variance_north = wind_cov[0];
	wind_est.variance_east = wind_cov[1];
	wind_est.tas_innov = _wind_estimator.get_tas_innov();
	wind_est.tas_innov_var = _wind_estimator.get_tas_innov_var();
	wind_est.beta_innov = _wind_estimator.get_beta_innov();
	wind_est.beta_innov_var = _wind_estimator.get_beta_innov_var();
	wind_est.tas_scale = _wind_estimator.get_tas_scale();
	return wind_est;
}

void
AirspeedValidator::set_airspeed_scale_manual(float airspeed_scale_manual)
{
	_airspeed_scale_manual = airspeed_scale_manual;
	_wind_estimator.enforce_airspeed_scale(1.0f / airspeed_scale_manual); // scale is inverted inside the wind estimator
}

void
AirspeedValidator::update_CAS_scale()
{
	if (_wind_estimator.is_estimate_valid()) {
		_CAS_scale = 1.0f / math::constrain(_wind_estimator.get_tas_scale(), 0.5f, 2.0f);

	} else {
		_CAS_scale = _airspeed_scale_manual;
	}
}

void
AirspeedValidator::update_CAS_TAS(float air_pressure_pa, float air_temperature_celsius)
{
	_CAS = calc_CAS_from_IAS(_IAS, _CAS_scale);
	_TAS = calc_TAS_from_CAS(_CAS, air_pressure_pa, air_temperature_celsius);
}

void
AirspeedValidator::check_airspeed_innovation(uint64_t time_now, float estimator_status_vel_test_ratio,
		float estimator_status_mag_test_ratio)
{
	// Check normalised innovation levels with requirement for continuous data and use of hysteresis
	// to prevent false triggering.

	if (_wind_estimator.get_wind_estimator_reset()) {
		_time_wind_estimator_initialized = time_now;
	}

	// reset states if we are not flying
	if (!_in_fixed_wing_flight) {
		_innovations_check_failed = false;
		_time_last_tas_pass = time_now;
		_time_last_tas_fail = 0;
		_airspeed_valid = true;
		_time_last_aspd_innov_check = time_now;

	} else {
		const float dt_s = math::max((time_now - _time_last_aspd_innov_check) / 1e6f, 0.01f); // limit to 100Hz

		if (dt_s < 1.0f) {
			// compute the ratio of innovation to gate size
			float tas_test_ratio = _wind_estimator.get_tas_innov() * _wind_estimator.get_tas_innov()
					       / (fmaxf(_tas_gate, 1.0f) * fmaxf(_tas_gate, 1.0f) * _wind_estimator.get_tas_innov_var());

			if (tas_test_ratio <= _tas_innov_threshold) {
				// record pass and reset integrator used to trigger
				_time_last_tas_pass = time_now;
				_apsd_innov_integ_state = 0.0f;

			} else {
				// integrate exceedance
				_apsd_innov_integ_state += dt_s * (tas_test_ratio - _tas_innov_threshold);
			}

			if ((estimator_status_vel_test_ratio < 1.0f) && (estimator_status_mag_test_ratio < 1.0f)) {
				// nav velocity data is likely good so airspeed innovations are able to be used
				if ((_tas_innov_integ_threshold > 0.0f) && (_apsd_innov_integ_state > _tas_innov_integ_threshold)) {
					_time_last_tas_fail = time_now;
				}
			}

			if (!_innovations_check_failed) {
				_innovations_check_failed = (time_now - _time_last_tas_pass) > TAS_INNOV_FAIL_DELAY;

			} else {
				_innovations_check_failed = ((time_now - _time_last_tas_fail) < TAS_INNOV_FAIL_DELAY * 100)
							    || (time_now - _time_wind_estimator_initialized) < TAS_INNOV_FAIL_DELAY * 100;
			}
		}

		_time_last_aspd_innov_check = time_now;
	}
}


void
AirspeedValidator::check_load_factor(float accel_z)
{
	// Check if the airpeed reading is lower than physically possible given the load factor

	if (_in_fixed_wing_flight) {

		float max_lift_ratio = fmaxf(_CAS, 0.7f) / fmaxf(_airspeed_stall, 1.0f);
		max_lift_ratio *= max_lift_ratio;
		_load_factor_ratio = 0.95f * _load_factor_ratio + 0.05f * (fabsf(accel_z) / 9.81f) / max_lift_ratio;
		_load_factor_ratio = math::constrain(_load_factor_ratio, 0.25f, 2.0f);
		_load_factor_check_failed = (_load_factor_ratio > 1.1f);

	} else {
		_load_factor_ratio = 0.5f; // reset if not in fixed-wing flight (and not in takeoff condition)
	}
}


void
AirspeedValidator::update_airspeed_valid_status(const uint64_t timestamp)
{
	// Declare data stopped if not received for longer than 1 second
	_data_stopped_failed = (timestamp - _time_last_airspeed) > 1_s;

	if (_innovations_check_failed || _load_factor_check_failed) {
		// either innovation or load factor check failed, so record timestamp
		_time_checks_failed = timestamp;

	} else if (!_innovations_check_failed && !_load_factor_check_failed) {
		// both innovation or load factor checks must pass to declare airspeed good
		_time_checks_passed = timestamp;
	}

	if (_airspeed_valid) {
		// A simultaneous load factor and innovaton check fail makes it more likely that a large
		// airspeed measurement fault has developed, so a fault should be declared immediately
		const bool both_checks_failed = (_innovations_check_failed && _load_factor_check_failed);

		// Because the innovation and load factor checks are subject to short duration false positives
		// a timeout period is applied.
		const bool single_check_fail_timeout = (timestamp - _time_checks_passed) > _checks_fail_delay * 1_s;

		if (_data_stopped_failed || both_checks_failed || single_check_fail_timeout) {

			_airspeed_valid = false;
		}

	} else if (!_data_stopped_failed && (timestamp - _time_checks_failed) > _checks_clear_delay * 1_s) {
		_airspeed_valid = true;
	}
}