ardupilot/libraries/AC_AttitudeControl/AC_PosControl.h

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
#ifndef AC_POSCONTROL_H
#define AC_POSCONTROL_H

#include <AP_Common.h>
#include <AP_Param.h>
#include <AP_Math.h>
#include <AC_PID.h>             // PID library
#include <AC_P.h>               // P library
#include <AP_InertialNav.h>     // Inertial Navigation library
#include <AC_AttitudeControl.h> // Attitude control library
#include <AP_Motors.h>          // motors library
#include <AP_Vehicle.h>         // common vehicle parameters


// position controller default definitions
#define POSCONTROL_THROTTLE_HOVER               450.0f  // default throttle required to maintain hover
#define POSCONTROL_LEASH_Z                      750.0f  // leash length for z-axis altitude controller.  To-Do: replace this with calculation based on alt_pos.kP()?
#define POSCONTROL_ACCELERATION                 100.0f  // defines the default velocity vs distant curve.  maximum acceleration in cm/s/s that position controller asks for from acceleration controller
#define POSCONTROL_ACCELERATION_MIN             50.0f   // minimum acceleration in cm/s/s - used for sanity checking _accel parameter
#define POSCONTROL_ACCEL_XY_MAX                 980.0f  // max horizontal acceleration in cm/s/s that the position velocity controller will ask from the lower accel controller
#define POSCONTROL_STOPPING_DIST_Z_MAX          200.0f  // max stopping distance vertically   
                                                        // should be 1.5 times larger than POSCONTROL_ACCELERATION.
                                                        // max acceleration = max lean angle * 980 * pi / 180.  i.e. 23deg * 980 * 3.141 / 180 = 393 cm/s/s
#define POSCONTROL_TAKEOFF_JUMP_CM               20.0f  // during take-off altitude target is set to current altitude + this value

#define POSCONTROL_SPEED                        500.0f  // maximum default horizontal speed in cm/s
#define POSCONTROL_SPEED_DOWN                  -150.0f  // maximum default descent rate
#define POSCONTROL_SPEED_UP                     250.0f  // maximum default climb rate
#define POSCONTROL_VEL_XY_MAX_FROM_POS_ERR      200.0f  // max speed output from pos_to_vel controller when feed forward is used

#define POSCONTROL_ALT_HOLD_ACCEL_MAX           250.0f  // hard coded copy of throttle controller's maximum acceleration in cm/s.  To-Do: remove duplication with throttle controller definition

#define POSCONTROL_LEASH_LENGTH_MIN             100.0f  // minimum leash lengths in cm

#define POSCONTROL_DT_10HZ                      0.10f   // time difference in seconds for 10hz update rate

class AC_PosControl
{
public:

    /// Constructor
    AC_PosControl(const AP_AHRS& ahrs, const AP_InertialNav& inav,
                  const AP_Motors& motors, AC_AttitudeControl& attitude_control,
                  AC_P& p_alt_pos, AC_P& p_alt_rate, AC_PID& pid_alt_accel,
                  AC_P& p_pos_xy, AC_PID& pid_rate_lat, AC_PID& pid_rate_lon);

    ///
    /// initialisation functions
    ///

    /// set_dt - sets time delta in seconds for all controllers (i.e. 100hz = 0.01, 400hz = 0.0025)
    void set_dt(float delta_sec) { _dt = delta_sec; }
    float get_dt() const { return _dt; }

    ///
    /// z position controller
    ///

    /// set_alt_max - sets maximum altitude above home in cm
    /// set to zero to disable limit
    /// To-Do: update this intermittantly from main code after checking if fence is enabled/disabled
    void set_alt_max(float alt) { _alt_max = alt; }

    /// set_speed_z - sets maximum climb and descent rates
    /// To-Do: call this in the main code as part of flight mode initialisation
    ///     calc_leash_length_z should be called afterwards
    ///     speed_down should be a negative number
    void set_speed_z(float speed_down, float speed_up);

    /// get_speed_up - accessor for current up speed in cm/s
    float get_speed_up() { return _speed_up_cms; }

    /// get_speed_down - accessors for current down speed in cm/s.  Will be a negative number
    float get_speed_down() { return _speed_down_cms; }

    /// set_accel_z - set vertical acceleration in cm/s/s
    ///     calc_leash_length_z should be called afterwards
    void set_accel_z(float accel_cmss);

    /// calc_leash_length - calculates the vertical leash lengths from maximum speed, acceleration
    ///     called by pos_to_rate_z if z-axis speed or accelerations are changed
    void calc_leash_length_z();

    /// set_throttle_hover - update estimated throttle required to maintain hover
    void set_throttle_hover(float throttle) { _throttle_hover = throttle; }

    /// set_alt_target - set altitude target in cm above home
    void set_alt_target(float alt_cm) { _pos_target.z = alt_cm; }

    /// set_alt_target_with_slew - adjusts target towards a final altitude target
    ///     should be called continuously (with dt set to be the expected time between calls)
    ///     actual position target will be moved no faster than the speed_down and speed_up
    ///     target will also be stopped if the motors hit their limits or leash length is exceeded
    void set_alt_target_with_slew(float alt_cm, float dt);

    /// set_alt_target_from_climb_rate - adjusts target up or down using a climb rate in cm/s
    ///     should be called continuously (with dt set to be the expected time between calls)
    ///     actual position target will be moved no faster than the speed_down and speed_up
    ///     target will also be stopped if the motors hit their limits or leash length is exceeded
    void set_alt_target_from_climb_rate(float climb_rate_cms, float dt);

    /// get_alt_target, get_desired_alt - get desired altitude (in cm above home) from loiter or wp controller which should be fed into throttle controller
    /// To-Do: remove one of the two functions below
    float get_alt_target() const { return _pos_target.z; }

    /// get_alt_error - returns altitude error in cm
    float get_alt_error() const;

    /// set_target_to_stopping_point_z - sets altitude target to reasonable stopping altitude in cm above home
    void set_target_to_stopping_point_z();

    /// get_stopping_point_z - sets stopping_point.z to a reasonable stopping altitude in cm above home
    void get_stopping_point_z(Vector3f& stopping_point) const;

    /// init_takeoff - initialises target altitude if we are taking off
    void init_takeoff();

    /// update_z_controller - fly to altitude in cm above home
    void update_z_controller();

    // get_leash_down_z, get_leash_up_z - returns vertical leash lengths in cm
    float get_leash_down_z() const { return _leash_down_z; }
    float get_leash_up_z() const { return _leash_up_z; }

    /// althold_kP - returns altitude hold position control PID's kP gain
    float althold_kP() const { return _p_alt_pos.kP(); }

    ///
    /// xy position controller
    ///

    /// set_accel_xy - set horizontal acceleration in cm/s/s
    ///     calc_leash_length_xy should be called afterwards
    void set_accel_xy(float accel_cmss);
    float get_accel_xy() const { return _accel_cms; }

    /// set_speed_xy - set horizontal speed maximum in cm/s
    ///     calc_leash_length_xy should be called afterwards
    void set_speed_xy(float speed_cms);
    float get_speed_xy() const { return _speed_cms; }

    /// calc_leash_length - calculates the horizontal leash length given a maximum speed, acceleration
    ///     should be called whenever the speed, acceleration or position kP is modified
    void calc_leash_length_xy();

    /// get_pos_target - get target as position vector (from home in cm)
    const Vector3f& get_pos_target() const { return _pos_target; }

    /// set_pos_target in cm from home
    void set_pos_target(const Vector3f& position);

    /// get_desired_velocity - returns xy desired velocity (i.e. feed forward) in cm/s in lat and lon direction
    const Vector2f& get_desired_velocity() { return _vel_desired; }

    /// set_desired_velocity - sets desired velocity in cm/s in lat and lon directions
    ///     when update_pos_controller is next called the position target is moved based on the desired velocity and
    ///     the desired velocities are fed forward into the rate_to_accel step
    void set_desired_velocity(float vel_lat_cms, float vel_lon_cms) {_vel_desired.x = vel_lat_cms; _vel_desired.y = vel_lon_cms; }

    /// trigger_xy - used to notify the position controller than an update has been made to the position or desired velocity so that the position controller will run as soon as possible after the update
    void trigger_xy() { _flags.force_recalc_xy = true; }

    /// update_pos_controller - run the position controller - should be called at 100hz or higher
    ///     when use_desired_velocity is true the desired velocity (i.e. feed forward) is incorporated at the pos_to_rate step
    void update_pos_controller(bool use_desired_velocity);

    /// get_stopping_point_xy - calculates stopping point based on current position, velocity, vehicle acceleration
    ///     distance_max allows limiting distance to stopping point
    ///		results placed in stopping_position vector
    ///     set_accel_xy() should be called before this method to set vehicle acceleration
    ///     set_leash_length() should have been called before this method
    void get_stopping_point_xy(Vector3f &stopping_point) const;

    /// get_distance_to_target - get horizontal distance to position target in cm (used for reporting)
    float get_distance_to_target() const;

    /// get desired roll, pitch which should be fed into stabilize controllers
    float get_roll() const { return _roll_target; }
    float get_pitch() const { return _pitch_target; }

    // get_leash_xy - returns horizontal leash length in cm
    float get_leash_xy() { return _leash; }

    /// get_pos_xy_kP - returns xy position controller's kP gain
    float get_pos_xy_kP() const { return _p_pos_xy.kP(); }

    /// accessors for reporting
    const Vector3f get_vel_target() { return _vel_target; }
    const Vector3f get_accel_target() { return _accel_target; }

    static const struct AP_Param::GroupInfo var_info[];

private:

    // general purpose flags
    struct poscontrol_flags {
            uint8_t recalc_leash_z  : 1;    // 1 if we should recalculate the z axis leash length
            uint8_t recalc_leash_xy : 1;    // 1 if we should recalculate the xy axis leash length
            uint8_t force_recalc_xy : 1;    // 1 if we want the xy position controller to run at it's next possible time.  set by loiter and wp controllers after they have updated the target position.
            uint8_t slow_cpu        : 1;    // 1 if we are running on a slow_cpu machine.  xy position control is broken up into multiple steps
    } _flags;

    // limit flags structure
    struct poscontrol_limit_flags {
        uint8_t pos_up      : 1;    // 1 if we have hit the vertical position leash limit while going up
        uint8_t pos_down    : 1;    // 1 if we have hit the vertical position leash limit while going down
        uint8_t vel_up      : 1;    // 1 if we have hit the vertical velocity limit going up
        uint8_t vel_down    : 1;    // 1 if we have hit the vertical velocity limit going down
        uint8_t accel_xy    : 1;    // 1 if we have hit the horizontal accel limit
    } _limit;

    ///
    /// z controller private methods
    ///

    // pos_to_rate_z - position to rate controller for Z axis
    // target altitude should be placed into _pos_target.z using or set with one of these functions
    //          set_alt_target
    //          set_target_to_stopping_point_z
    //          init_takeoff
    void pos_to_rate_z();

    // rate_to_accel_z - calculates desired accel required to achieve the velocity target
    void rate_to_accel_z(float vel_target_z);

    // accel_to_throttle - alt hold's acceleration controller
    void accel_to_throttle(float accel_target_z);

    ///
    /// xy controller private methods
    ///

    /// desired_vel_to_pos - move position target using desired velocities
    void desired_vel_to_pos(float nav_dt);

    /// pos_to_rate_xy - horizontal position error to velocity controller
    ///     converts position (_pos_target) to target velocity (_vel_target)
    ///     when use_desired_rate is set to true:
    ///         desired velocity (_vel_desired) is combined into final target velocity and
    ///         velocity due to position error is reduce to a maximum of 1m/s
    void pos_to_rate_xy(bool use_desired_rate, float dt);

    /// rate_to_accel_xy - horizontal desired rate to desired acceleration
    ///    converts desired velocities in lat/lon directions to accelerations in lat/lon frame
    void rate_to_accel_xy(float dt);

    /// accel_to_lean_angles - horizontal desired acceleration to lean angles
    ///    converts desired accelerations provided in lat/lon frame to roll/pitch angles
    void accel_to_lean_angles();

    /// reset_I_xy - clears I terms from horizontal position PID controller
    void reset_I_xy();

    /// calc_leash_length - calculates the horizontal leash length given a maximum speed, acceleration and position kP gain
    float calc_leash_length(float speed_cms, float accel_cms, float kP) const;

    // references to inertial nav and ahrs libraries
    const AP_AHRS&              _ahrs;
    const AP_InertialNav&       _inav;
    const AP_Motors&            _motors;
    AC_AttitudeControl&         _attitude_control;

    // references to pid controllers and motors
    AC_P&       _p_alt_pos;
    AC_P&       _p_alt_rate;
    AC_PID&     _pid_alt_accel;
    AC_P&	    _p_pos_xy;
    AC_PID&	    _pid_rate_lat;
    AC_PID&	    _pid_rate_lon;

    // parameters
    AP_Float    _throttle_hover;        // estimated throttle required to maintain a level hover

    // internal variables
    float       _dt;                    // time difference (in seconds) between calls from the main program
    uint32_t    _last_update_ms;        // system time of last update_position_controller call
    uint32_t    _last_update_rate_ms;   // system time of last call to rate_to_accel_z (alt hold accel controller)
    uint32_t    _last_update_accel_ms;  // system time of last call to accel_to_throttle (alt hold accel controller)
    uint8_t     _step;                  // used to decide which portion of position controller to run during this iteration
    float       _speed_down_cms;        // max descent rate in cm/s
    float       _speed_up_cms;          // max climb rate in cm/s
    float       _speed_cms;             // max horizontal speed in cm/s
    float       _accel_z_cms;           // max vertical acceleration in cm/s/s
    float       _accel_cms;             // max horizontal acceleration in cm/s/s
    float       _leash;                 // horizontal leash length in cm.  target will never be further than this distance from the vehicle
    float       _leash_down_z;          // vertical leash down in cm.  target will never be further than this distance below the vehicle
    float       _leash_up_z;            // vertical leash up in cm.  target will never be further than this distance above the vehicle
    float       _cos_yaw;               // short-cut to save on calcs required to convert roll-pitch frame to lat-lon frame
    float       _sin_yaw;
    float       _cos_pitch;

    // output from controller
    float       _roll_target;           // desired roll angle in centi-degrees calculated by position controller
    float       _pitch_target;          // desired roll pitch in centi-degrees calculated by position controller

    // position controller internal variables
    Vector3f    _pos_target;            // target location in cm from home
    Vector3f    _pos_error;             // error between desired and actual position in cm
    Vector2f    _vel_desired;           // desired velocity in cm/s in lat and lon directions (provided by external callers of move_target_at_rate() method)
    Vector3f    _vel_target;            // velocity target in cm/s calculated by pos_to_rate step
    Vector3f    _vel_error;             // error between desired and actual acceleration in cm/s
    Vector3f    _vel_last;              // previous iterations velocity in cm/s
    float       _vel_target_filt_z;     // filtered target vertical velocity
    Vector3f    _accel_target;          // desired acceleration in cm/s/s  // To-Do: are xy actually required?
    Vector3f    _accel_error;           // desired acceleration in cm/s/s  // To-Do: are xy actually required?
    float       _alt_max;               // max altitude - should be updated from the main code with altitude limit from fence
    float       _distance_to_target;    // distance to position target - for reporting only
    uint8_t     _xy_step;               // used to decide which portion of horizontal position controller to run during this iteration
    float       _dt_xy;                 // time difference in seconds between horizontal position updates
};
#endif	// AC_POSCONTROL_H