FixedwingLandDetector.cpp

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/**
 * @file FixedwingLandDetector.cpp
 *
 * @author Johan Jansen <jnsn.johan@gmail.com>
 * @author Lorenz Meier <lorenz@px4.io>
 * @author Julian Oes <julian@oes.ch>
 */

#include "FixedwingLandDetector.h"

namespace land_detector
{

FixedwingLandDetector::FixedwingLandDetector()
{
	// Use Trigger time when transitioning from in-air (false) to landed (true) / ground contact (true).
	_landed_hysteresis.set_hysteresis_time_from(false, _param_lndfw_trig_time.get() * 1_s);
}

bool FixedwingLandDetector::_get_landed_state()
{
	// Only trigger flight conditions if we are armed.
	if (!_armed) {
		return true;
	}

	// Force the landed state to stay landed if we're currently in an early state of the takeoff state machines.
	// This prevents premature transitions to in-air during the early takeoff phase.
	if (_landed_hysteresis.get_state()) {
		launch_detection_status_s launch_detection_status{};
		_launch_detection_status_sub.copy(&launch_detection_status);

		fixed_wing_runway_control_s fixed_wing_runway_control{};
		_fixed_wing_runway_control_sub.copy(&fixed_wing_runway_control);

		// Check if we're in catapult/hand-launch waiting state
		const bool waiting_for_catapult_launch = hrt_elapsed_time(&launch_detection_status.timestamp) < 500_ms
				&& launch_detection_status.launch_detection_state == launch_detection_status_s::STATE_WAITING_FOR_LAUNCH;

		// Check if we're in runway takeoff early phase (throttle ramp or clamped to runway)
		const bool waiting_for_auto_runway_climbout = hrt_elapsed_time(&fixed_wing_runway_control.timestamp) < 500_ms
				&& fixed_wing_runway_control.runway_takeoff_state < fixed_wing_runway_control_s::STATE_CLIMBOUT;

		if (waiting_for_catapult_launch || waiting_for_auto_runway_climbout) {
			return true;
		}
	}

	bool landDetected = false;

	if (hrt_elapsed_time(&_vehicle_local_position.timestamp) < 1_s) {

		float val = 0.0f;

		if (_vehicle_local_position.v_xy_valid) {
			// Horizontal velocity complimentary filter.
			val = 0.97f * _velocity_xy_filtered + 0.03f * sqrtf(_vehicle_local_position.vx * _vehicle_local_position.vx +
					_vehicle_local_position.vy * _vehicle_local_position.vy);
		}

		if (PX4_ISFINITE(val)) {
			_velocity_xy_filtered = val;
		}

		// Vertical velocity complimentary filter.
		val = 0.99f * _velocity_z_filtered + 0.01f * fabsf(_vehicle_local_position.vz);

		if (PX4_ISFINITE(val)) {
			_velocity_z_filtered = val;
		}

		airspeed_validated_s airspeed_validated{};
		_airspeed_validated_sub.copy(&airspeed_validated);

		const bool airspeed_from_sensor = airspeed_validated.airspeed_source == airspeed_validated_s::SOURCE_SENSOR_1
						  || airspeed_validated.airspeed_source == airspeed_validated_s::SOURCE_SENSOR_2
						  || airspeed_validated.airspeed_source == airspeed_validated_s::SOURCE_SENSOR_3;

		bool airspeed_invalid = false;

		// set _airspeed_filtered to 0 if airspeed data is invalid or not from an actual airspeed sensor
		if (!airspeed_from_sensor || !PX4_ISFINITE(airspeed_validated.true_airspeed_m_s)
		    || hrt_elapsed_time(&airspeed_validated.timestamp) > 1_s) {
			_airspeed_filtered = 0.0f;
			airspeed_invalid = true;

		} else {
			_airspeed_filtered = 0.95f * _airspeed_filtered + 0.05f * airspeed_validated.true_airspeed_m_s;
		}

		// A leaking lowpass prevents biases from building up, but
		// gives a mostly correct response for short impulses.
		const float acc_hor = matrix::Vector2f(_acceleration).norm();
		_xy_accel_filtered = _xy_accel_filtered * 0.8f + acc_hor * 0.18f;

		// Check for angular velocity
		const float rot_vel_hor = _angular_velocity.norm();
		val = _velocity_rot_filtered * 0.95f + rot_vel_hor * 0.05f;

		if (PX4_ISFINITE(val)) {
			_velocity_rot_filtered = val;
		}

		// make groundspeed threshold tighter if airspeed is invalid
		const float vel_xy_max_threshold   = airspeed_invalid ? 0.7f * _param_lndfw_vel_xy_max.get() :
						     _param_lndfw_vel_xy_max.get();

		// only use the max rotational threshold if neither airspeed nor groundspeed can be used for landing detection
		const float max_rotation_threshold = (!_vehicle_local_position.v_xy_valid
						      && airspeed_invalid) ? math::radians(_param_lndfw_rot_max.get()) : INFINITY;

		// Crude land detector for fixedwing.
		landDetected = _airspeed_filtered         < _param_lndfw_airspd.get()
			       && _velocity_xy_filtered   < vel_xy_max_threshold
			       && _velocity_z_filtered    < _param_lndfw_vel_z_max.get()
			       && _xy_accel_filtered      < _param_lndfw_xyaccel_max.get()
			       && _velocity_rot_filtered  < max_rotation_threshold;

	} else {
		// Control state topic has timed out and we need to assume we're landed.
		landDetected = true;
	}

	return landDetected;
}

} // namespace land_detector