ardupilot/ArduCopter/land_detector.pde

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

// counter to verify landings
static uint16_t land_detector = LAND_DETECTOR_TRIGGER;  // we assume we are landed

// land_complete_maybe - return true if we may have landed (used to reset loiter targets during landing)
static bool land_complete_maybe()
{
    return (ap.land_complete || ap.land_complete_maybe);
}

// update_land_detector - checks if we have landed and updates the ap.land_complete flag
// called at 50hz
static void update_land_detector()
{
    bool climb_rate_low = (abs(climb_rate) < LAND_DETECTOR_CLIMBRATE_MAX);
    bool target_climb_rate_low = !pos_control.is_active_z() || (pos_control.get_desired_velocity().z <= LAND_DETECTOR_DESIRED_CLIMBRATE_MAX);
    bool motor_at_lower_limit = motors.limit.throttle_lower;
    bool throttle_low = (FRAME_CONFIG == HELI_FRAME) || (motors.get_throttle_out() < get_non_takeoff_throttle());
    bool not_rotating_fast = (ahrs.get_gyro().length() < LAND_DETECTOR_ROTATION_MAX);

    if (climb_rate_low && target_climb_rate_low && motor_at_lower_limit && throttle_low && not_rotating_fast) {
        if (!ap.land_complete) {
            // increase counter until we hit the trigger then set land complete flag
            if( land_detector < LAND_DETECTOR_TRIGGER) {
                land_detector++;
            }else{
                set_land_complete(true);
                land_detector = LAND_DETECTOR_TRIGGER;
            }
        }
    } else {
        // we've sensed movement up or down so reset land_detector
        land_detector = 0;
        // if throttle output is high then clear landing flag
        if (motors.get_throttle_out() > get_non_takeoff_throttle()) {
            set_land_complete(false);
        }
    }

    // set land maybe flag
    set_land_complete_maybe(land_detector >= LAND_DETECTOR_MAYBE_TRIGGER);
}