ardupilot/ArduCopter/control_loiter.pde

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

/*
 * control_loiter.pde - init and run calls for loiter flight mode
 */

// loiter_init - initialise loiter controller
static bool loiter_init(bool ignore_checks)
{
    if (position_ok() || optflow_position_ok() || ignore_checks) {

        // set target to current position
        wp_nav.init_loiter_target();

        // initialize vertical speed and accelerationj
        pos_control.set_speed_z(-g.pilot_velocity_z_max, g.pilot_velocity_z_max);
        pos_control.set_accel_z(g.pilot_accel_z);

        // initialise altitude target to stopping point
        pos_control.set_target_to_stopping_point_z();

        return true;
    }else{
        return false;
    }
}

// loiter_run - runs the loiter controller
// should be called at 100hz or more
static void loiter_run()
{
    float target_yaw_rate = 0;
    float target_climb_rate = 0;

    // if not auto armed set throttle to zero and exit immediately
    if(!ap.auto_armed) {
        wp_nav.init_loiter_target();
        attitude_control.relax_bf_rate_controller();
        attitude_control.set_yaw_target_to_current_heading();
        attitude_control.set_throttle_out(0, false);
        pos_control.set_alt_target_to_current_alt();
        return;
    }

    // process pilot inputs
    if (!failsafe.radio) {
        // apply SIMPLE mode transform to pilot inputs
        update_simple_mode();

        // process pilot's roll and pitch input
        wp_nav.set_pilot_desired_acceleration(g.rc_1.control_in, g.rc_2.control_in);

        // get pilot's desired yaw rate
        target_yaw_rate = get_pilot_desired_yaw_rate(g.rc_4.control_in);

        // get pilot desired climb rate
        target_climb_rate = get_pilot_desired_climb_rate(g.rc_3.control_in);

        // check for pilot requested take-off
        if (ap.land_complete && target_climb_rate > 0) {
            // indicate we are taking off
            set_land_complete(false);
            // clear i term when we're taking off
            set_throttle_takeoff();
        }
    } else {
        // clear out pilot desired acceleration in case radio failsafe event occurs and we do not switch to RTL for some reason
        wp_nav.clear_pilot_desired_acceleration();
    }

    // relax loiter target if we might be landed
    if (land_complete_maybe()) {
        wp_nav.loiter_soften_for_landing();
    }

    // when landed reset targets and output zero throttle
    if (ap.land_complete) {
        wp_nav.init_loiter_target();
        attitude_control.relax_bf_rate_controller();
        attitude_control.set_yaw_target_to_current_heading();
        // move throttle to between minimum and non-takeoff-throttle to keep us on the ground
        attitude_control.set_throttle_out(get_throttle_pre_takeoff(g.rc_3.control_in), false);
        pos_control.set_alt_target_to_current_alt();
    }else{
        // run loiter controller
        wp_nav.update_loiter(ekfGndSpdLimit, ekfNavVelGainScaler);

        // call attitude controller
        attitude_control.angle_ef_roll_pitch_rate_ef_yaw(wp_nav.get_roll(), wp_nav.get_pitch(), target_yaw_rate);

        // body-frame rate controller is run directly from 100hz loop

        // run altitude controller
        if (sonar_alt_health >= SONAR_ALT_HEALTH_MAX) {
            // if sonar is ok, use surface tracking
            target_climb_rate = get_throttle_surface_tracking(target_climb_rate, pos_control.get_alt_target(), G_Dt);
        }

        // update altitude target and call position controller
        pos_control.set_alt_target_from_climb_rate(target_climb_rate, G_Dt);
        pos_control.update_z_controller();
    }
}