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

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/**
 * @file MulticopterLandDetector.cpp
 * Land detection algorithm for multicopters
 *
 * @author Johan Jansen <jnsn.johan@gmail.com>
 * @author Morten Lysgaard <morten@lysgaard.no>
 */

#include "MulticopterLandDetector.h"

#include <cmath>
#include <drivers/drv_hrt.h>
#include <mathlib/mathlib.h>

namespace landdetection
{

MulticopterLandDetector::MulticopterLandDetector() : LandDetector(),
	_paramHandle(),
	_params(),
	_vehicleLocalPositionSub(-1),
	_actuatorsSub(-1),
	_armingSub(-1),
	_parameterSub(-1),
	_attitudeSub(-1),
	_manualSub(-1),
	_ctrl_state_sub(-1),
	_vehicle_control_mode_sub(-1),
	_vehicleLocalPosition{},
	_actuators{},
	_arming{},
	_vehicleAttitude{},
	_manual{},
	_ctrl_state{},
	_ctrl_mode{},
	_min_trust_start(0),
	_freefall_hysteresis(false),
	_landed_hysteresis(true)
{
	// Use Trigger time when transitioning from in-air (false) to landed (true).
	_landed_hysteresis.set_hysteresis_time_from(false, LAND_DETECTOR_TRIGGER_TIME);

	_paramHandle.maxRotation = param_find("LNDMC_ROT_MAX");
	_paramHandle.maxVelocity = param_find("LNDMC_XY_VEL_MAX");
	_paramHandle.maxClimbRate = param_find("LNDMC_Z_VEL_MAX");
	_paramHandle.maxThrottle = param_find("MPC_THR_MIN");
	_paramHandle.minManThrottle = param_find("MPC_MANTHR_MIN");
	_paramHandle.acc_threshold_m_s2 = param_find("LNDMC_FFALL_THR");
	_paramHandle.ff_trigger_time = param_find("LNDMC_FFALL_TTRI");
}

void MulticopterLandDetector::initialize()
{
	// subscribe to position, attitude, arming and velocity changes
	_vehicleLocalPositionSub = orb_subscribe(ORB_ID(vehicle_local_position));
	_attitudeSub = orb_subscribe(ORB_ID(vehicle_attitude));
	_actuatorsSub = orb_subscribe(ORB_ID(actuator_controls_0));
	_armingSub = orb_subscribe(ORB_ID(actuator_armed));
	_parameterSub = orb_subscribe(ORB_ID(parameter_update));
	_manualSub = orb_subscribe(ORB_ID(manual_control_setpoint));
	_ctrl_state_sub = orb_subscribe(ORB_ID(control_state));
	_vehicle_control_mode_sub = orb_subscribe(ORB_ID(vehicle_control_mode));

	// download parameters
	updateParameterCache(true);
}

void MulticopterLandDetector::updateSubscriptions()
{
	orb_update(ORB_ID(vehicle_local_position), _vehicleLocalPositionSub, &_vehicleLocalPosition);
	orb_update(ORB_ID(vehicle_attitude), _attitudeSub, &_vehicleAttitude);
	orb_update(ORB_ID(actuator_controls_0), _actuatorsSub, &_actuators);
	orb_update(ORB_ID(actuator_armed), _armingSub, &_arming);
	orb_update(ORB_ID(manual_control_setpoint), _manualSub, &_manual);
	orb_update(ORB_ID(control_state), _ctrl_state_sub, &_ctrl_state);
	orb_update(ORB_ID(vehicle_control_mode), _vehicle_control_mode_sub, &_ctrl_mode);
}

LandDetectionResult MulticopterLandDetector::update()
{
	// first poll for new data from our subscriptions
	updateSubscriptions();

	updateParameterCache(false);

	_landed_hysteresis.set_state_and_update(get_landed_state());
	_freefall_hysteresis.set_state_and_update(get_freefall_state());

	if (_freefall_hysteresis.get_state()) {
		_state = LANDDETECTION_RES_FREEFALL;

	} else if (_landed_hysteresis.get_state()) {
		_state = LANDDETECTION_RES_LANDED;

	} else {
		_state = LANDDETECTION_RES_FLYING;
	}

	return _state;
}

bool MulticopterLandDetector::get_freefall_state()
{
	if (_params.acc_threshold_m_s2 < 0.1f
	    || _params.acc_threshold_m_s2 > 10.0f) {	//if parameter is set to zero or invalid, disable free-fall detection.
		return false;
	}

	if (_ctrl_state.timestamp == 0) {
		// _ctrl_state is not valid yet, we have to assume we're not falling.
		return false;
	}

	float acc_norm = _ctrl_state.x_acc * _ctrl_state.x_acc
			 + _ctrl_state.y_acc * _ctrl_state.y_acc
			 + _ctrl_state.z_acc * _ctrl_state.z_acc;
	acc_norm = sqrtf(acc_norm);	//norm of specific force. Should be close to 9.8 m/s^2 when landed.

	return (acc_norm < _params.acc_threshold_m_s2);	//true if we are currently falling
}

bool MulticopterLandDetector::get_landed_state()
{
	// Time base for this function
	const uint64_t now = hrt_absolute_time();

	float sys_min_throttle = (_params.maxThrottle + 0.01f);

	// Determine the system min throttle based on flight mode
	if (!_ctrl_mode.flag_control_altitude_enabled) {
		sys_min_throttle = (_params.minManThrottle + 0.01f);
	}

	// Check if thrust output is less than the minimum auto throttle param.
	bool minimalThrust = (_actuators.control[3] <= sys_min_throttle);

	if (minimalThrust && _min_trust_start == 0) {
		_min_trust_start = now;

	} else if (!minimalThrust) {
		_min_trust_start = 0;
	}

	// only trigger flight conditions if we are armed
	if (!_arming.armed) {
		_arming_time = 0;
		return true;

	} else if (_arming_time == 0) {
		_arming_time = now;
	}

	// If in manual flight mode never report landed if the user has more than idle throttle
	// Check if user commands throttle and if so, report not landed based on
	// the user intent to take off (even if the system might physically still have
	// ground contact at this point).
	if (_manual.timestamp > 0 && _manual.z > 0.15f && _ctrl_mode.flag_control_manual_enabled) {
		return false;
	}

	// Return status based on armed state and throttle if no position lock is available.
	if (_vehicleLocalPosition.timestamp == 0 ||
	    hrt_elapsed_time(&_vehicleLocalPosition.timestamp) > 500000 ||
	    !_vehicleLocalPosition.xy_valid ||
	    !_vehicleLocalPosition.z_valid) {

		// The system has minimum trust set (manual or in failsafe)
		// if this persists for 8 seconds AND the drone is not
		// falling consider it to be landed. This should even sustain
		// quite acrobatic flight.
		if ((_min_trust_start > 0) &&
		    (hrt_elapsed_time(&_min_trust_start) > 8 * 1000 * 1000)) {
			return !get_freefall_state();

		} else {
			return false;
		}
	}

	float armThresholdFactor = 1.0f;

	// Widen acceptance thresholds for landed state right after arming
	// so that motor spool-up and other effects do not trigger false negatives.
	if (hrt_elapsed_time(&_arming_time) < LAND_DETECTOR_ARM_PHASE_TIME) {
		armThresholdFactor = 2.5f;
	}

	// Check if we are moving vertically - this might see a spike after arming due to
	// throttle-up vibration. If accelerating fast the throttle thresholds will still give
	// an accurate in-air indication.
	bool verticalMovement = fabsf(_vehicleLocalPosition.vz) > _params.maxClimbRate * armThresholdFactor;

	// Check if we are moving horizontally.
	bool horizontalMovement = sqrtf(_vehicleLocalPosition.vx * _vehicleLocalPosition.vx
					+ _vehicleLocalPosition.vy * _vehicleLocalPosition.vy) > _params.maxVelocity;

	// Next look if all rotation angles are not moving.
	float maxRotationScaled = _params.maxRotation_rad_s * armThresholdFactor;

	bool rotating = (fabsf(_vehicleAttitude.rollspeed)  > maxRotationScaled) ||
			(fabsf(_vehicleAttitude.pitchspeed) > maxRotationScaled) ||
			(fabsf(_vehicleAttitude.yawspeed) > maxRotationScaled);


	if (verticalMovement || rotating || !minimalThrust || horizontalMovement) {
		// Sensed movement or thottle high, so reset the land detector.
		return false;
	}

	return true;
}

void MulticopterLandDetector::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.maxClimbRate, &_params.maxClimbRate);
		param_get(_paramHandle.maxVelocity, &_params.maxVelocity);
		param_get(_paramHandle.maxRotation, &_params.maxRotation_rad_s);
		_params.maxRotation_rad_s = math::radians(_params.maxRotation_rad_s);
		param_get(_paramHandle.maxThrottle, &_params.maxThrottle);
		param_get(_paramHandle.minManThrottle, &_params.minManThrottle);
		param_get(_paramHandle.acc_threshold_m_s2, &_params.acc_threshold_m_s2);
		param_get(_paramHandle.ff_trigger_time, &_params.ff_trigger_time);
		_freefall_hysteresis.set_hysteresis_time_from(false, 1e6f*_params.ff_trigger_time);
	}
}

}