ardupilot/libraries/AC_AttitudeControl/AC_PosControl_Sub.cpp

#include "AC_PosControl_Sub.h"

AC_PosControl_Sub::AC_PosControl_Sub(AP_AHRS_View& ahrs, const AP_InertialNav& inav,
                                     const AP_Motors& motors, AC_AttitudeControl& attitude_control, float dt) :
    AC_PosControl(ahrs, inav, motors, attitude_control, dt),
    _alt_max(0.0f),
    _alt_min(0.0f)
{}

/// input_vel_z calculate a jerk limited path from the current position, velocity and acceleration to an input velocity.
///     The function takes the current position, velocity, and acceleration and calculates the required jerk limited adjustment to the acceleration for the next time dt.
///     The kinematic path is constrained by :
///         maximum velocity - vel_max,
///         maximum acceleration - accel_max,
///         time constant - tc.
///     The time constant defines the acceleration error decay in the kinematic path as the system approaches constant acceleration.
///     The time constant also defines the time taken to achieve the maximum acceleration.
///     The time constant must be positive.
///     The function alters the input velocity to be the velocity that the system could reach zero acceleration in the minimum time.
void AC_PosControl_Sub::input_vel_accel_z(Vector3f& vel, const Vector3f& accel, bool force_descend)
{
    // check for ekf z position reset
    check_for_ekf_z_reset();

    // limit desired velocity to prevent breeching altitude limits
    if (_alt_min < 0 && _alt_min < _alt_max && _alt_max < 100 && _pos_target.z < _alt_min) {
        vel.z = constrain_float(vel.z,
            sqrt_controller(_alt_min-_pos_target.z, 0.0f, _accel_max_z_cmss, 0.0f),
            sqrt_controller(_alt_max-_pos_target.z, 0.0f, _accel_max_z_cmss, 0.0f));
    }

    // calculated increased maximum acceleration if over speed
    float accel_z_cms = _accel_max_z_cmss;
    if (_vel_desired.z < _vel_max_down_cms && !is_zero(_vel_max_down_cms)) {
        accel_z_cms *= POSCONTROL_OVERSPEED_GAIN_Z * _vel_desired.z / _vel_max_down_cms;
    }
    if (_vel_desired.z > _vel_max_up_cms && !is_zero(_vel_max_up_cms)) {
        accel_z_cms *= POSCONTROL_OVERSPEED_GAIN_Z * _vel_desired.z / _vel_max_up_cms;
    }

    // adjust desired alt if motors have not hit their limits
    update_pos_vel_accel_z(_pos_target, _vel_desired, _accel_desired, _dt, _limit_vector);

    // prevent altitude target from breeching altitude limits
    if (_alt_min < 0 && _alt_min < _alt_max && _alt_max < 100 && _pos_target.z < _alt_min) {
        _pos_target.z = constrain_float(_pos_target.z, _alt_min, _alt_max);
    }

    shape_vel_accel(vel.z, accel.z,
        _vel_desired.z, _accel_desired.z,
        _vel_max_down_cms, _vel_max_up_cms,
        -accel_z_cms, accel_z_cms,
        _tc_z_s, _dt);

    update_vel_accel_z(vel, accel, _dt, _limit_vector);
}