PX4-Autopilot/src/modules/navigator/rtl.cpp

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/**
 * @file rtl.cpp
 *
 * Helper class to access RTL
 *
 * @author Julian Oes <julian@oes.ch>
 * @author Anton Babushkin <anton.babushkin@me.com>
 * @author Julian Kent <julian@auterion.com>
 */

#include "rtl.h"
#include "navigator.h"
#include <dataman/dataman.h>
#include <px4_platform_common/events.h>

#include <lib/geo/geo.h>


static constexpr float DELAY_SIGMA = 0.01f;

using namespace time_literals;
using namespace math;

RTL::RTL(Navigator *navigator) :
	MissionBlock(navigator),
	ModuleParams(navigator)
{
	_param_mpc_z_v_auto_up = param_find("MPC_Z_V_AUTO_UP");
	_param_mpc_z_v_auto_dn = param_find("MPC_Z_V_AUTO_DN");
	_param_mpc_land_speed = param_find("MPC_LAND_SPEED");
	_param_fw_climb_rate = param_find("FW_T_CLMB_R_SP");
	_param_fw_sink_rate = param_find("FW_T_SINK_R_SP");
	_param_fw_airspeed_trim = param_find("FW_AIRSPD_TRIM");
	_param_mpc_xy_cruise = param_find("MPC_XY_CRUISE");
	_param_rover_cruise_speed = param_find("GND_SPEED_THR_SC");
}

void RTL::on_inactivation()
{
	if (_navigator->get_precland()->is_activated()) {
		_navigator->get_precland()->on_inactivation();
	}
}

void RTL::on_inactive()
{
	// Limit inactive calculation to 1Hz
	if ((hrt_absolute_time() - _destination_check_time) > 1_s) {
		_destination_check_time = hrt_absolute_time();

		const vehicle_global_position_s &global_position = *_navigator->get_global_position();

		const bool global_position_recently_updated = global_position.timestamp > 0
				&& hrt_elapsed_time(&global_position.timestamp) < 10_s;

		rtl_time_estimate_s rtl_time_estimate{};
		rtl_time_estimate.valid = false;

		// Calculate RTL destination and time estimate only when there is a valid home and global position
		if (_navigator->home_global_position_valid() && global_position_recently_updated) {
			find_RTL_destination();
			calcRtlTimeEstimate(RTLState::RTL_STATE_NONE, rtl_time_estimate);
			rtl_time_estimate.valid = true;
		}

		rtl_time_estimate.timestamp = hrt_absolute_time();
		_rtl_time_estimate_pub.publish(rtl_time_estimate);
	}
}

void RTL::find_RTL_destination()
{
	// get home position:
	home_position_s &home_landing_position = *_navigator->get_home_position();

	// get global position
	const vehicle_global_position_s &global_position = *_navigator->get_global_position();

	// set destination to home per default, then check if other valid landing spot is closer
	_destination.set(home_landing_position);

	// get distance to home position
	double dlat = home_landing_position.lat - global_position.lat;
	double dlon = home_landing_position.lon - global_position.lon;

	double lon_scale = cos(radians(global_position.lat));

	auto coord_dist_sq = [lon_scale](double lat_diff, double lon_diff) -> double {
		double lon_diff_scaled =  lon_scale * matrix::wrap(lon_diff, -180., 180.);
		return lat_diff * lat_diff + lon_diff_scaled * lon_diff_scaled;
	};

	double min_dist_squared = coord_dist_sq(dlat, dlon);

	_destination.type = RTL_DESTINATION_HOME;

	const bool vtol_in_rw_mode = _navigator->get_vstatus()->is_vtol
				     && _navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROTARY_WING;


	// consider the mission landing if not RTL_TYPE_HOME_OR_RALLY type set
	if (_param_rtl_type.get() != RTL_TYPE_HOME_OR_RALLY && _navigator->get_mission_start_land_available()) {
		double mission_landing_lat;
		double mission_landing_lon;
		float mission_landing_alt;

		if (vtol_in_rw_mode) {
			mission_landing_lat = _navigator->get_mission_landing_lat();
			mission_landing_lon = _navigator->get_mission_landing_lon();
			mission_landing_alt = _navigator->get_mission_landing_alt();

		} else {
			mission_landing_lat = _navigator->get_mission_landing_start_lat();
			mission_landing_lon = _navigator->get_mission_landing_start_lon();
			mission_landing_alt = _navigator->get_mission_landing_start_alt();
		}

		dlat = mission_landing_lat - global_position.lat;
		dlon = mission_landing_lon - global_position.lon;
		double dist_squared = coord_dist_sq(dlat, dlon);

		// always find closest destination if in hover and VTOL
		if (_param_rtl_type.get() == RTL_TYPE_CLOSEST || (vtol_in_rw_mode && !_navigator->on_mission_landing())) {

			// compare home position to landing position to decide which is closer
			if (dist_squared < min_dist_squared) {
				_destination.type = RTL_DESTINATION_MISSION_LANDING;
				min_dist_squared = dist_squared;
				_destination.lat = mission_landing_lat;
				_destination.lon = mission_landing_lon;
				_destination.alt = mission_landing_alt;
			}

		} else {
			// it has to be the mission landing
			_destination.type = RTL_DESTINATION_MISSION_LANDING;
			min_dist_squared = dist_squared;
			_destination.lat = mission_landing_lat;
			_destination.lon = mission_landing_lon;
			_destination.alt = mission_landing_alt;
		}
	}

	// do not consider rally point if RTL type is set to RTL_TYPE_MISSION_LANDING_REVERSED, so exit function and use either home or mission landing
	if (_param_rtl_type.get() == RTL_TYPE_MISSION_LANDING_REVERSED) {
		return;
	}

	// compare to safe landing positions
	mission_safe_point_s closest_safe_point {};
	mission_stats_entry_s stats;
	int ret = dm_read(DM_KEY_SAFE_POINTS, 0, &stats, sizeof(mission_stats_entry_s));
	int num_safe_points = 0;

	if (ret == sizeof(mission_stats_entry_s)) {
		num_safe_points = stats.num_items;
	}

	// check if a safe point is closer than home or landing
	int closest_index = 0;

	for (int current_seq = 1; current_seq <= num_safe_points; ++current_seq) {
		mission_safe_point_s mission_safe_point;

		if (dm_read(DM_KEY_SAFE_POINTS, current_seq, &mission_safe_point, sizeof(mission_safe_point_s)) !=
		    sizeof(mission_safe_point_s)) {
			PX4_ERR("dm_read failed");
			continue;
		}

		// TODO: take altitude into account for distance measurement
		dlat = mission_safe_point.lat - global_position.lat;
		dlon = mission_safe_point.lon - global_position.lon;
		double dist_squared = coord_dist_sq(dlat, dlon);

		if (dist_squared < min_dist_squared) {
			closest_index = current_seq;
			min_dist_squared = dist_squared;
			closest_safe_point = mission_safe_point;
		}
	}

	if (closest_index > 0) {
		_destination.type = RTL_DESTINATION_SAFE_POINT;

		// There is a safe point closer than home/mission landing
		// TODO: handle all possible mission_safe_point.frame cases
		switch (closest_safe_point.frame) {
		case 0: // MAV_FRAME_GLOBAL
			_destination.lat = closest_safe_point.lat;
			_destination.lon = closest_safe_point.lon;
			_destination.alt = closest_safe_point.alt;
			_destination.yaw = home_landing_position.yaw;
			break;

		case 3: // MAV_FRAME_GLOBAL_RELATIVE_ALT
			_destination.lat = closest_safe_point.lat;
			_destination.lon = closest_safe_point.lon;
			_destination.alt = closest_safe_point.alt + home_landing_position.alt; // alt of safe point is rel to home
			_destination.yaw = home_landing_position.yaw;
			break;

		default:
			mavlink_log_critical(_navigator->get_mavlink_log_pub(), "RTL: unsupported MAV_FRAME\t");
			events::send<uint8_t>(events::ID("rtl_unsupported_mav_frame"), events::Log::Error, "RTL: unsupported MAV_FRAME ({1})",
					      closest_safe_point.frame);
			break;
		}
	}

	if (_param_rtl_cone_half_angle_deg.get() > 0
	    && _navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROTARY_WING) {
		_rtl_alt = calculate_return_alt_from_cone_half_angle((float)_param_rtl_cone_half_angle_deg.get());

	} else {
		_rtl_alt = max(global_position.alt, _destination.alt + _param_rtl_return_alt.get());
	}
}

void RTL::on_activation()
{
	_rtl_state = RTL_STATE_NONE;

	// output the correct message, depending on where the RTL destination is
	switch (_destination.type) {
	case RTL_DESTINATION_HOME:
		mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: landing at home position.\t");
		events::send(events::ID("rtl_land_at_home"), events::Log::Info, "RTL: landing at home position");
		break;

	case RTL_DESTINATION_MISSION_LANDING:
		mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: landing at mission landing.\t");
		events::send(events::ID("rtl_land_at_mission"), events::Log::Info, "RTL: landing at mission landing");
		break;

	case RTL_DESTINATION_SAFE_POINT:
		mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: landing at safe landing point.\t");
		events::send(events::ID("rtl_land_at_safe_point"), events::Log::Info, "RTL: landing at safe landing point");
		break;
	}

	const vehicle_global_position_s &global_position = *_navigator->get_global_position();

	if (_navigator->get_land_detected()->landed) {
		// For safety reasons don't go into RTL if landed.
		_rtl_state = RTL_STATE_LANDED;

	} else if ((global_position.alt < _destination.alt + _param_rtl_return_alt.get()) || _rtl_alt_min) {

		// If lower than return altitude, climb up first.
		// If rtl_alt_min is true then forcing altitude change even if above.
		_rtl_state = RTL_STATE_CLIMB;

	} else {
		// Otherwise go straight to return
		_rtl_state = RTL_STATE_RETURN;
	}

	// reset cruising speed and throttle to default for RTL
	_navigator->set_cruising_speed();
	_navigator->set_cruising_throttle();

	set_rtl_item();

}

void RTL::on_active()
{
	if (_rtl_state != RTL_STATE_LANDED && is_mission_item_reached_or_completed()) {
		advance_rtl();
		set_rtl_item();
	}

	if (_rtl_state == RTL_STATE_LAND && _param_rtl_pld_md.get() > 0) {
		_navigator->get_precland()->on_active();

	} else if (_navigator->get_precland()->is_activated()) {
		_navigator->get_precland()->on_inactivation();
	}

	// Limit rtl time calculation to 1Hz
	if ((hrt_absolute_time() - _destination_check_time) > 1_s) {
		_destination_check_time = hrt_absolute_time();

		const vehicle_global_position_s &global_position = *_navigator->get_global_position();

		const bool global_position_recently_updated = global_position.timestamp > 0
				&& hrt_elapsed_time(&global_position.timestamp) < 10_s;

		rtl_time_estimate_s rtl_time_estimate{};
		rtl_time_estimate.valid = false;

		// Calculate RTL destination and time estimate only when there is a valid home and global position
		if (_navigator->home_global_position_valid() && global_position_recently_updated) {
			find_RTL_destination();
			calcRtlTimeEstimate(_rtl_state, rtl_time_estimate);
			rtl_time_estimate.valid = true;
		}

		rtl_time_estimate.timestamp = hrt_absolute_time();
		_rtl_time_estimate_pub.publish(rtl_time_estimate);
	}
}

void RTL::set_rtl_item()
{
	_navigator->set_can_loiter_at_sp(false);

	const vehicle_global_position_s &gpos = *_navigator->get_global_position();

	position_setpoint_triplet_s *pos_sp_triplet = _navigator->get_position_setpoint_triplet();

	const float destination_dist = get_distance_to_next_waypoint(_destination.lat, _destination.lon, gpos.lat, gpos.lon);
	const float loiter_altitude = math::min(_destination.alt + _param_rtl_descend_alt.get(), _rtl_alt);

	// if we will switch to mission for landing, already set the loiter radius (incl. direction) from mission
	const float landing_loiter_radius = _destination.type == RTL_DESTINATION_MISSION_LANDING ?
					    _navigator->get_mission_landing_loiter_radius() : _param_rtl_loiter_rad.get();

	const RTLHeadingMode rtl_heading_mode = static_cast<RTLHeadingMode>(_param_rtl_hdg_md.get());

	switch (_rtl_state) {
	case RTL_STATE_CLIMB: {

			_mission_item.nav_cmd = NAV_CMD_LOITER_TO_ALT;

			_mission_item.lat = gpos.lat;
			_mission_item.lon = gpos.lon;
			_mission_item.altitude = _rtl_alt;
			_mission_item.altitude_is_relative = false;

			if (rtl_heading_mode != RTLHeadingMode::RTL_DESTINATION_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;

			} else {
				_mission_item.yaw = _destination.yaw;
			}

			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.time_inside = 0.0f;
			_mission_item.autocontinue = true;
			_mission_item.origin = ORIGIN_ONBOARD;
			_mission_item.loiter_radius = _navigator->get_loiter_radius();

			mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: climb to %d m (%d m above destination)\t",
					 (int)ceilf(_rtl_alt), (int)ceilf(_rtl_alt - _destination.alt));
			events::send<int32_t, int32_t>(events::ID("rtl_climb_to"), events::Log::Info,
						       "RTL: climb to {1m_v} ({2m_v} above destination)",
						       (int32_t)ceilf(_rtl_alt), (int32_t)ceilf(_rtl_alt - _destination.alt));
			break;
		}

	case RTL_STATE_RETURN: {

			// For FW flight:set to LOITER_TIME (with 0s loiter time), such that the loiter (orbit) status
			// can be displayed on groundstation and the WP is accepted once within loiter radius
			if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING) {
				_mission_item.nav_cmd = NAV_CMD_LOITER_TIME_LIMIT;


			} else {
				_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
			}

			_mission_item.lat = _destination.lat;
			_mission_item.lon = _destination.lon;
			_mission_item.altitude = _rtl_alt; // Don't change altitude
			_mission_item.altitude_is_relative = false;

			if (rtl_heading_mode == RTLHeadingMode::RTL_NAVIGATION_HEADING &&
			    destination_dist > _param_rtl_min_dist.get()) {
				_mission_item.yaw = get_bearing_to_next_waypoint(gpos.lat, gpos.lon, _destination.lat, _destination.lon);

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_DESTINATION_HEADING ||
				   destination_dist < _param_rtl_min_dist.get()) {
				// Use destination yaw if close to _destination.
				_mission_item.yaw = _destination.yaw;

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_CURRENT_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;
			}

			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.time_inside = 0.0f;
			_mission_item.autocontinue = true;
			_mission_item.origin = ORIGIN_ONBOARD;
			_mission_item.loiter_radius = landing_loiter_radius;

			mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: return at %d m (%d m above destination)\t",
					 (int)ceilf(_mission_item.altitude), (int)ceilf(_mission_item.altitude - _destination.alt));
			events::send<int32_t, int32_t>(events::ID("rtl_return_at"), events::Log::Info,
						       "RTL: return at {1m_v} ({2m_v} above destination)",
						       (int32_t)ceilf(_mission_item.altitude), (int32_t)ceilf(_mission_item.altitude - _destination.alt));

			break;
		}

	case RTL_STATE_DESCEND: {
			_mission_item.nav_cmd = NAV_CMD_LOITER_TO_ALT;
			_mission_item.lat = _destination.lat;
			_mission_item.lon = _destination.lon;
			_mission_item.altitude = loiter_altitude;
			_mission_item.altitude_is_relative = false;

			// Except for vtol which might be still off here and should point towards this location.
			const float d_current = get_distance_to_next_waypoint(gpos.lat, gpos.lon, _mission_item.lat, _mission_item.lon);

			if (_navigator->get_vstatus()->is_vtol && (d_current > _navigator->get_acceptance_radius())) {
				_mission_item.yaw = get_bearing_to_next_waypoint(gpos.lat, gpos.lon, _mission_item.lat, _mission_item.lon);

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_CURRENT_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;

			} else {
				_mission_item.yaw = _destination.yaw;
			}

			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.time_inside = 0.0f;
			_mission_item.autocontinue = true;
			_mission_item.origin = ORIGIN_ONBOARD;
			_mission_item.loiter_radius = landing_loiter_radius;

			// Disable previous setpoint to prevent drift.
			pos_sp_triplet->previous.valid = false;

			mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: descend to %d m (%d m above destination)\t",
					 (int)ceilf(_mission_item.altitude), (int)ceilf(_mission_item.altitude - _destination.alt));
			events::send<int32_t, int32_t>(events::ID("rtl_descend_to"), events::Log::Info,
						       "RTL: descend to {1m_v} ({2m_v} above destination)",
						       (int32_t)ceilf(_mission_item.altitude), (int32_t)ceilf(_mission_item.altitude - _destination.alt));
			break;
		}

	case RTL_STATE_LOITER: {
			const bool autocontinue = (_param_rtl_land_delay.get() > FLT_EPSILON);

			if (autocontinue) {
				_mission_item.nav_cmd = NAV_CMD_LOITER_TIME_LIMIT;
				mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: loiter %.1fs\t",
						 (double)_param_rtl_land_delay.get());
				events::send<float>(events::ID("rtl_loiter"), events::Log::Info, "RTL: loiter {1:.1}s", _param_rtl_land_delay.get());

			} else {
				_mission_item.nav_cmd = NAV_CMD_LOITER_UNLIMITED;
				mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: completed, loitering\t");
				events::send(events::ID("rtl_completed_loiter"), events::Log::Info, "RTL: completed, loitering");
			}

			_mission_item.lat = _destination.lat;
			_mission_item.lon = _destination.lon;
			_mission_item.altitude = loiter_altitude;    // Don't change altitude.
			_mission_item.altitude_is_relative = false;

			if (rtl_heading_mode == RTLHeadingMode::RTL_CURRENT_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;

			} else {
				_mission_item.yaw = _destination.yaw;
			}

			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.time_inside = max(_param_rtl_land_delay.get(), 0.0f);
			_mission_item.autocontinue = autocontinue;
			_mission_item.origin = ORIGIN_ONBOARD;
			_mission_item.loiter_radius = landing_loiter_radius;

			_navigator->set_can_loiter_at_sp(true);

			break;
		}

	case RTL_STATE_HEAD_TO_CENTER: {
			_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
			_mission_item.lat = _destination.lat;
			_mission_item.lon = _destination.lon;
			_mission_item.altitude = loiter_altitude;
			_mission_item.altitude_is_relative = false;

			if (rtl_heading_mode == RTLHeadingMode::RTL_NAVIGATION_HEADING) {
				_mission_item.yaw = get_bearing_to_next_waypoint(gpos.lat, gpos.lon, _destination.lat, _destination.lon);

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_DESTINATION_HEADING) {
				_mission_item.yaw = _destination.yaw;

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_CURRENT_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;
			}

			_mission_item.vtol_back_transition = true;
			// acceptance_radius will be overwritten since vtol_back_transition is set,
			// set as a default value only
			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.time_inside = 0.0f;
			_mission_item.autocontinue = true;
			_mission_item.origin = ORIGIN_ONBOARD;

			// Disable previous setpoint to prevent drift.
			pos_sp_triplet->previous.valid = false;
			break;
		}

	case RTL_STATE_TRANSITION_TO_MC: {
			set_vtol_transition_item(&_mission_item, vtol_vehicle_status_s::VEHICLE_VTOL_STATE_MC);
			break;
		}

	case RTL_MOVE_TO_LAND_HOVER_VTOL: {
			_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
			_mission_item.lat = _destination.lat;
			_mission_item.lon = _destination.lon;
			_mission_item.altitude = loiter_altitude;
			_mission_item.altitude_is_relative = false;

			if (rtl_heading_mode == RTLHeadingMode::RTL_NAVIGATION_HEADING) {
				_mission_item.yaw = get_bearing_to_next_waypoint(gpos.lat, gpos.lon, _destination.lat, _destination.lon);

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_DESTINATION_HEADING) {
				_mission_item.yaw = _destination.yaw;

			} else if (rtl_heading_mode == RTLHeadingMode::RTL_CURRENT_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;
			}

			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.origin = ORIGIN_ONBOARD;
			break;
		}

	case RTL_STATE_LAND: {
			// Land at destination.
			_mission_item.nav_cmd = NAV_CMD_LAND;
			_mission_item.lat = _destination.lat;
			_mission_item.lon = _destination.lon;
			_mission_item.altitude = _destination.alt;
			_mission_item.altitude_is_relative = false;

			if (rtl_heading_mode == RTLHeadingMode::RTL_CURRENT_HEADING) {
				_mission_item.yaw = _navigator->get_local_position()->heading;

			} else {
				_mission_item.yaw = _destination.yaw;
			}

			_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
			_mission_item.time_inside = 0.0f;
			_mission_item.autocontinue = true;
			_mission_item.origin = ORIGIN_ONBOARD;
			_mission_item.land_precision = _param_rtl_pld_md.get();

			if (_mission_item.land_precision == 1) {
				_navigator->get_precland()->set_mode(PrecLandMode::Opportunistic);
				_navigator->get_precland()->on_activation();

			} else if (_mission_item.land_precision == 2) {
				_navigator->get_precland()->set_mode(PrecLandMode::Required);
				_navigator->get_precland()->on_activation();
			}

			mavlink_log_info(_navigator->get_mavlink_log_pub(), "RTL: land at destination\t");
			events::send(events::ID("rtl_land_at_destination"), events::Log::Info, "RTL: land at destination");
			break;
		}

	case RTL_STATE_LANDED: {
			set_idle_item(&_mission_item);
			set_return_alt_min(false);
			break;
		}

	default:
		break;
	}

	reset_mission_item_reached();

	// Execute command if set. This is required for commands like VTOL transition.
	if (!item_contains_position(_mission_item)) {
		issue_command(_mission_item);
	}

	// Convert mission item to current position setpoint and make it valid.
	mission_apply_limitation(_mission_item);

	if (mission_item_to_position_setpoint(_mission_item, &pos_sp_triplet->current)) {
		_navigator->set_position_setpoint_triplet_updated();
	}
}

void RTL::advance_rtl()
{
	// determines if the vehicle should loiter above land
	const bool descend_and_loiter = _param_rtl_land_delay.get() < -DELAY_SIGMA || _param_rtl_land_delay.get() > DELAY_SIGMA;

	// vehicle is a vtol and currently in fixed wing mode
	const bool vtol_in_fw_mode = _navigator->get_vstatus()->is_vtol
				     && _navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING;

	switch (_rtl_state) {
	case RTL_STATE_CLIMB:
		_rtl_state = RTL_STATE_RETURN;
		break;

	case RTL_STATE_RETURN:
		_rtl_state = RTL_STATE_DESCEND;
		break;

	case RTL_STATE_DESCEND:

		if (descend_and_loiter) {
			_rtl_state = RTL_STATE_LOITER;

		} else if (vtol_in_fw_mode) {
			_rtl_state = RTL_STATE_HEAD_TO_CENTER;

		} else {
			_rtl_state = RTL_STATE_LAND;
		}

		break;

	case RTL_STATE_LOITER:

		if (vtol_in_fw_mode) {
			_rtl_state = RTL_STATE_HEAD_TO_CENTER;

		} else {
			_rtl_state = RTL_STATE_LAND;
		}

		break;

	case RTL_STATE_HEAD_TO_CENTER:

		_rtl_state = RTL_STATE_TRANSITION_TO_MC;

		break;

	case RTL_STATE_TRANSITION_TO_MC:

		_rtl_state = RTL_MOVE_TO_LAND_HOVER_VTOL;

		break;

	case RTL_MOVE_TO_LAND_HOVER_VTOL:

		_rtl_state = RTL_STATE_LAND;

		break;

	case RTL_STATE_LAND:
		_rtl_state = RTL_STATE_LANDED;
		_navigator->mode_completed(vehicle_status_s::NAVIGATION_STATE_AUTO_RTL);
		break;

	default:
		break;
	}
}

float RTL::calculate_return_alt_from_cone_half_angle(float cone_half_angle_deg)
{
	const vehicle_global_position_s &gpos = *_navigator->get_global_position();

	// horizontal distance to destination
	const float destination_dist = get_distance_to_next_waypoint(_destination.lat, _destination.lon, gpos.lat, gpos.lon);

	// minium rtl altitude to use when outside of horizontal acceptance radius of target position.
	// We choose the minimum height to be two times the distance from the land position in order to
	// avoid the vehicle touching the ground while still moving horizontally.
	const float return_altitude_min_outside_acceptance_rad_amsl = _destination.alt + 2.0f *
			_navigator->get_acceptance_radius();

	float return_altitude_amsl = _destination.alt + _param_rtl_return_alt.get();

	if (destination_dist <= _navigator->get_acceptance_radius()) {
		return_altitude_amsl = _destination.alt + 2.0f * destination_dist;

	} else {

		if (destination_dist <= _param_rtl_min_dist.get()) {

			// constrain cone half angle to meaningful values. All other cases are already handled above.
			const float cone_half_angle_rad = radians(constrain(cone_half_angle_deg, 1.0f, 89.0f));

			// minimum altitude we need in order to be within the user defined cone
			const float cone_intersection_altitude_amsl = destination_dist / tanf(cone_half_angle_rad) + _destination.alt;

			return_altitude_amsl = min(cone_intersection_altitude_amsl, return_altitude_amsl);
		}

		return_altitude_amsl = max(return_altitude_amsl, return_altitude_min_outside_acceptance_rad_amsl);
	}

	return max(return_altitude_amsl, gpos.alt);
}

void RTL::calcRtlTimeEstimate(const RTLState rtl_state, rtl_time_estimate_s &rtl_time_estimate)
{
	const vehicle_global_position_s &gpos = *_navigator->get_global_position();

	// Sum up time estimate for various segments of the landing procedure
	switch (rtl_state) {
	case RTL_STATE_NONE:
	case RTL_STATE_CLIMB: {
			// Climb segment is only relevant if the drone is below return altitude
			const float climb_dist = gpos.alt < _rtl_alt ? (_rtl_alt - gpos.alt) : 0;

			if (climb_dist > FLT_EPSILON) {
				rtl_time_estimate.time_estimate += climb_dist / getClimbRate();
			}
		}

	// FALLTHROUGH
	case RTL_STATE_RETURN:

		// Add cruise segment to home
		rtl_time_estimate.time_estimate += get_distance_to_next_waypoint(
				_destination.lat, _destination.lon, gpos.lat, gpos.lon) / getCruiseGroundSpeed();

	// FALLTHROUGH
	case RTL_STATE_HEAD_TO_CENTER:
	case RTL_STATE_TRANSITION_TO_MC:
	case RTL_STATE_DESCEND: {
			// when descending, the target altitude is stored in the current mission item
			float initial_altitude = 0.f;
			float loiter_altitude = 0.f;

			if (rtl_state == RTL_STATE_DESCEND) {
				// Take current vehicle altitude as the starting point for calculation
				initial_altitude = gpos.alt;  // TODO: Check if this is in the right frame
				loiter_altitude = _mission_item.altitude;  // Next waypoint = loiter


			} else {
				// Take the return altitude as the starting point for the calculation
				initial_altitude = _rtl_alt; // CLIMB and RETURN
				loiter_altitude = math::min(_destination.alt + _param_rtl_descend_alt.get(), _rtl_alt);
			}

			// Add descend segment (first landing phase: return alt to loiter alt)
			rtl_time_estimate.time_estimate += fabsf(initial_altitude - loiter_altitude) / getDescendRate();
		}

	// FALLTHROUGH
	case RTL_STATE_LOITER:
		// Add land delay (the short pause for deploying landing gear)
		// TODO: Check if landing gear is deployed or not
		rtl_time_estimate.time_estimate += _param_rtl_land_delay.get();

	// FALLTHROUGH
	case RTL_MOVE_TO_LAND_HOVER_VTOL:
	case RTL_STATE_LAND: {
			float initial_altitude;

			// Add land segment (second landing phase) which comes after LOITER
			if (rtl_state == RTL_STATE_LAND) {
				// If we are in this phase, use the current vehicle altitude  instead
				// of the altitude paramteter to get a continous time estimate
				initial_altitude = gpos.alt;


			} else {
				// If this phase is not active yet, simply use the loiter altitude,
				// which is where the LAND phase will start
				const float loiter_altitude = math::min(_destination.alt + _param_rtl_descend_alt.get(), _rtl_alt);
				initial_altitude = loiter_altitude;
			}

			// Prevent negative times when close to the ground
			if (initial_altitude > _destination.alt) {
				rtl_time_estimate.time_estimate += (initial_altitude - _destination.alt) / getHoverLandSpeed();
			}
		}

		break;

	case RTL_STATE_LANDED:
		// Remaining time is 0
		break;
	}

	// Prevent negative durations as phyiscally they make no sense. These can
	// occur during the last phase of landing when close to the ground.
	rtl_time_estimate.time_estimate = math::max(0.f, rtl_time_estimate.time_estimate);

	// Use actual time estimate to compute the safer time estimate with additional scale factor and a margin
	rtl_time_estimate.safe_time_estimate = _param_rtl_time_factor.get() * rtl_time_estimate.time_estimate
					       + _param_rtl_time_margin.get();
}

float RTL::getCruiseSpeed()
{
	float ret = 1e6f;

	if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROTARY_WING) {
		if (_param_mpc_xy_cruise == PARAM_INVALID || param_get(_param_mpc_xy_cruise, &ret) != PX4_OK) {
			ret = 1e6f;
		}

	} else if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING) {
		if (_param_fw_airspeed_trim == PARAM_INVALID || param_get(_param_fw_airspeed_trim, &ret) != PX4_OK) {
			ret = 1e6f;
		}

	} else if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROVER) {
		if (_param_rover_cruise_speed == PARAM_INVALID || param_get(_param_rover_cruise_speed, &ret) != PX4_OK) {
			ret = 1e6f;
		}
	}

	return ret;
}

float RTL::getHoverLandSpeed()
{
	float ret = 1e6f;

	if (_param_mpc_land_speed == PARAM_INVALID || param_get(_param_mpc_land_speed, &ret) != PX4_OK) {
		ret = 1e6f;
	}

	return ret;
}

matrix::Vector2f RTL::get_wind()
{
	_wind_sub.update();
	matrix::Vector2f wind;

	if (hrt_absolute_time() - _wind_sub.get().timestamp < 1_s) {
		wind(0) = _wind_sub.get().windspeed_north;
		wind(1) = _wind_sub.get().windspeed_east;
	}

	return wind;
}

float RTL::getClimbRate()
{
	float ret = 1e6f;

	if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROTARY_WING) {
		if (_param_mpc_z_v_auto_up == PARAM_INVALID || param_get(_param_mpc_z_v_auto_up, &ret) != PX4_OK) {
			ret = 1e6f;
		}

	} else if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING) {

		if (_param_fw_climb_rate == PARAM_INVALID || param_get(_param_fw_climb_rate, &ret) != PX4_OK) {
			ret = 1e6f;
		}
	}

	return ret;
}

float RTL::getDescendRate()
{
	float ret = 1e6f;

	if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_ROTARY_WING) {
		if (_param_mpc_z_v_auto_dn == PARAM_INVALID || param_get(_param_mpc_z_v_auto_dn, &ret) != PX4_OK) {
			ret = 1e6f;
		}

	} else if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING) {
		if (_param_fw_sink_rate == PARAM_INVALID || param_get(_param_fw_sink_rate, &ret) != PX4_OK) {
			ret = 1e6f;
		}
	}

	return ret;
}

float RTL::getCruiseGroundSpeed()
{
	float cruise_speed = getCruiseSpeed();

	if (_navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING) {
		const vehicle_global_position_s &global_position = *_navigator->get_global_position();
		matrix::Vector2f wind = get_wind();

		matrix::Vector2f to_destination_vec;
		get_vector_to_next_waypoint(global_position.lat, global_position.lon, _destination.lat, _destination.lon,
					    &to_destination_vec(0), &to_destination_vec(1));

		const matrix::Vector2f to_home_dir = to_destination_vec.unit_or_zero();

		const float wind_towards_home = wind.dot(to_home_dir);
		const float wind_across_home = matrix::Vector2f(wind - to_home_dir * wind_towards_home).norm();


		// Note: use fminf so that we don't _rely_ on wind towards home to make RTL more efficient
		const float ground_speed = sqrtf(cruise_speed * cruise_speed - wind_across_home * wind_across_home) + fminf(
						   0.f, wind_towards_home);

		cruise_speed = ground_speed;
	}

	return cruise_speed;
}