PX4-Autopilot/src/modules/land_detector/FixedwingLandDetector.cpp

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/**
 * @file FixedwingLandDetector.cpp
 * Land detection algorithm for fixedwings
 *
 * @author Johan Jansen <jnsn.johan@gmail.com>
 * @author Lorenz Meier <lorenz@px4.io>
 */

#include "FixedwingLandDetector.h"

#include <px4_config.h>
#include <px4_defines.h>
#include <cmath>
#include <drivers/drv_hrt.h>

FixedwingLandDetector::FixedwingLandDetector() : LandDetector(),
	_paramHandle(),
	_params(),
	_controlStateSub(-1),
	_vehicleStatusSub(-1),
	_armingSub(-1),
	_airspeedSub(-1),
	_controlState{},
	_vehicleStatus{},
	_arming{},
	_airspeed{},
	_parameterSub(-1),
	_velocity_xy_filtered(0.0f),
	_velocity_z_filtered(0.0f),
	_airspeed_filtered(0.0f),
	_accel_horz_lp(0.0f),
	_landDetectTrigger(0)
{
	_paramHandle.maxVelocity = param_find("LNDFW_VEL_XY_MAX");
	_paramHandle.maxClimbRate = param_find("LNDFW_VEL_Z_MAX");
	_paramHandle.maxAirSpeed = param_find("LNDFW_AIRSPD_MAX");
	_paramHandle.maxIntVelocity = param_find("LNDFW_VELI_MAX");
}

void FixedwingLandDetector::initialize()
{
	// Subscribe to local position and airspeed data
	_controlStateSub = orb_subscribe(ORB_ID(control_state));
	_vehicleStatusSub = orb_subscribe(ORB_ID(vehicle_status));
	_armingSub = orb_subscribe(ORB_ID(actuator_armed));
	_airspeedSub = orb_subscribe(ORB_ID(airspeed));

	updateParameterCache(true);
}

void FixedwingLandDetector::updateSubscriptions()
{
	orb_update(ORB_ID(control_state), _controlStateSub, &_controlState);
	orb_update(ORB_ID(vehicle_status), _vehicleStatusSub, &_vehicleStatus);
	orb_update(ORB_ID(actuator_armed), _armingSub, &_arming);
	orb_update(ORB_ID(airspeed), _airspeedSub, &_airspeed);
}

bool FixedwingLandDetector::update()
{
	// First poll for new data from our subscriptions
	updateSubscriptions();

	// only trigger flight conditions if we are armed
	if (!_arming.armed) {
		return true;
	}

	const uint64_t now = hrt_absolute_time();
	bool landDetected = false;

	if (hrt_elapsed_time(&_controlState.timestamp) < 500 * 1000) {
		float val = 0.97f * _velocity_xy_filtered + 0.03f * sqrtf(_controlState.x_vel *
				_controlState.x_vel + _controlState.y_vel * _controlState.y_vel);

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

		val = 0.99f * _velocity_z_filtered + 0.01f * fabsf(_controlState.z_vel);

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

		_airspeed_filtered = 0.95f * _airspeed_filtered + 0.05f * _airspeed.true_airspeed_m_s;

		// a leaking lowpass prevents biases from building up, but
		// gives a mostly correct response for short impulses
		_accel_horz_lp = _accel_horz_lp * 0.8f + _controlState.horz_acc_mag * 0.18f;

	}

	// crude land detector for fixedwing
	if (_velocity_xy_filtered < _params.maxVelocity
	    && _velocity_z_filtered < _params.maxClimbRate
	    && _airspeed_filtered < _params.maxAirSpeed
	    && _accel_horz_lp < _params.maxIntVelocity) {

		// these conditions need to be stable for a period of time before we trust them
		if (now > _landDetectTrigger) {
			landDetected = true;
		}

	} else {
		// reset land detect trigger
		_landDetectTrigger = now + LAND_DETECTOR_TRIGGER_TIME;
	}

	return landDetected;
}

void FixedwingLandDetector::updateParameterCache(const bool force)
{
	bool updated;
	parameter_update_s paramUpdate;

	orb_check(_parameterSub, &updated);

	if (updated) {
		orb_copy(ORB_ID(parameter_update), _parameterSub, &paramUpdate);
	}

	if (updated || force) {
		param_get(_paramHandle.maxVelocity, &_params.maxVelocity);
		param_get(_paramHandle.maxClimbRate, &_params.maxClimbRate);
		param_get(_paramHandle.maxAirSpeed, &_params.maxAirSpeed);
		param_get(_paramHandle.maxIntVelocity, &_params.maxIntVelocity);
	}
}