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   *   Copyright (c) 2013-2016 PX4 Development Team. All rights reserved.
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  /**
   * @file MulticopterLandDetector.h
   * Land detection implementation for multicopters.
   *
   * @author Johan Jansen <jnsn.johan@gmail.com>
   * @author Morten Lysgaard <morten@lysgaard.no>
   * @author Julian Oes <julian@oes.ch>
   */
  
  #pragma once
  
  #include <uORB/topics/actuator_controls.h>
  #include <uORB/topics/hover_thrust_estimate.h>
  #include <uORB/topics/vehicle_angular_velocity.h>
  #include <uORB/topics/vehicle_control_mode.h>
  #include <uORB/topics/vehicle_local_position_setpoint.h>
  
  #include "LandDetector.h"
  
  using namespace time_literals;
  
  namespace land_detector
  {
  
  class MulticopterLandDetector : public LandDetector
  {
  public:
  	MulticopterLandDetector();
  	~MulticopterLandDetector() override = default;
  
  protected:
  	void _update_params() override;
  	void _update_topics() override;
  
  	bool _get_landed_state() override;
  	bool _get_ground_contact_state() override;
  	bool _get_maybe_landed_state() override;
  	bool _get_freefall_state() override;
  	bool _get_ground_effect_state() override;
  
  	float _get_max_altitude() override;
  private:
  
  	/** Time in us that freefall has to hold before triggering freefall */
  	static constexpr hrt_abstime FREEFALL_TRIGGER_TIME_US = 300_ms;
  
  	/** Time in us that ground contact condition have to hold before triggering contact ground */
  	static constexpr hrt_abstime GROUND_CONTACT_TRIGGER_TIME_US = 350_ms;
  
  	/** Time in us that almost landing conditions have to hold before triggering almost landed . */
  	static constexpr hrt_abstime MAYBE_LAND_DETECTOR_TRIGGER_TIME_US = 250_ms;
  
  	/** Time in us that landing conditions have to hold before triggering a land. */
  	static constexpr hrt_abstime LAND_DETECTOR_TRIGGER_TIME_US = 300_ms;
  
  	/** Time interval in us in which wider acceptance thresholds are used after landed. */
  	static constexpr hrt_abstime LAND_DETECTOR_LAND_PHASE_TIME_US = 2_s;
  
  	/** Handles for interesting parameters. **/
  	struct {
  		param_t minThrottle;
  		param_t hoverThrottle;
  		param_t minManThrottle;
  		param_t landSpeed;
  		param_t useHoverThrustEstimate;
  	} _paramHandle{};
  
  	struct {
  		float minThrottle;
  		float hoverThrottle;
  		float minManThrottle;
  		float landSpeed;
  		bool useHoverThrustEstimate;
  	} _params{};
  
  	uORB::Subscription _actuator_controls_sub{ORB_ID(actuator_controls_0)};
  	uORB::Subscription _hover_thrust_estimate_sub{ORB_ID(hover_thrust_estimate)};
  	uORB::Subscription _vehicle_angular_velocity_sub{ORB_ID(vehicle_angular_velocity)};
  	uORB::Subscription _vehicle_control_mode_sub{ORB_ID(vehicle_control_mode)};
  	uORB::Subscription _vehicle_local_position_setpoint_sub{ORB_ID(vehicle_local_position_setpoint)};
  
  	bool _flag_control_climb_rate_enabled{false};
  	bool _hover_thrust_initialized{false};
  	bool _hover_thrust_estimate_valid{false};
  
  	float _actuator_controls_throttle{0.f};
  
  	hrt_abstime _min_thrust_start{0};	///< timestamp when minimum trust was applied first
  	hrt_abstime _landed_time{0};
  
  	bool _in_descend{false};		///< vehicle is desending
  	bool _horizontal_movement{false};	///< vehicle is moving horizontally
  
  	DEFINE_PARAMETERS_CUSTOM_PARENT(
  		LandDetector,
  		(ParamFloat<px4::params::LNDMC_ALT_MAX>)    _param_lndmc_alt_max,
  		(ParamFloat<px4::params::LNDMC_ROT_MAX>)    _param_lndmc_rot_max,
  		(ParamFloat<px4::params::LNDMC_XY_VEL_MAX>) _param_lndmc_xy_vel_max,
  		(ParamFloat<px4::params::LNDMC_Z_VEL_MAX>)  _param_lndmc_z_vel_max
  	);
  };
  
  } // namespace land_detector
  