飛機基本狀態的定義在vehicle_status.msg中

uint8 MAIN_STATE_MANUAL = 0
uint8 MAIN_STATE_ALTCTL = 1
uint8 MAIN_STATE_POSCTL = 2
uint8 MAIN_STATE_AUTO_MISSION = 3
uint8 MAIN_STATE_AUTO_LOITER = 4
uint8 MAIN_STATE_AUTO_RTL = 5
uint8 MAIN_STATE_ACRO = 6
uint8 MAIN_STATE_OFFBOARD = 7
uint8 MAIN_STATE_STAB = 8
uint8 MAIN_STATE_RATTITUDE = 9
uint8 MAIN_STATE_AUTO_TAKEOFF = 10
uint8 MAIN_STATE_AUTO_LAND = 11
uint8 MAIN_STATE_MAX = 12

state_machine_helper.cpp 描述允許狀態轉換的條件

....
case vehicle_status_s::MAIN_STATE_POSCTL:
      /* need at minimum local position estimate */
      // 也就是只要 Local 或 Global 其中一個定位有效，即可切換 POSCTL
      if (status->condition_local_position_valid ||
          status->condition_global_position_valid) {
          ret = TRANSITION_CHANGED;
      }
      break;
....

• status->condition_global_position_valid 的判斷在commander.cpp

  主要是看GPS的時間更新是否有效

  ...
  //update condition_global_position_valid
          //Global positions are only published by the estimators if they are valid
  if (hrt_absolute_time() - global_position.timestamp > POSITION_TIMEOUT) {
    //We have had no good fix for POSITION_TIMEOUT amount of time
    if (status.condition_global_position_valid) {
      set_tune_override(TONE_GPS_WARNING_TUNE);
      status_changed = true;
      status.condition_global_position_valid = false;
    }
  } else if (global_position.timestamp != 0) {
    // Got good global position estimate
    if (!status.condition_global_position_valid) {
      status_changed = true;
      status.condition_global_position_valid = true;
    }
  }
  ...
  

• status->condition_local_position_valid 在commander.cpp

  /* update condition_local_position_valid and condition_local_altitude_valid */
  /* hysteresis for EPH */
  bool local_eph_good;
  
  // 無論當前 condition_local_position_valid 是否有效，都有判斷 local_position.eph 的大小
  if (status.condition_local_position_valid) {
    if (local_position.eph > eph_threshold * 2.5f) {
      local_eph_good = false;
    } else {
      local_eph_good = true;
    }
  
  } else {
    if (local_position.eph < eph_threshold) {
      local_eph_good = true;
  
    } else {
      local_eph_good = false;
    }
  }
  
  // 根據上述判斷結果，對 condition_local_position_valid 進行更新
  check_valid(local_position.timestamp, POSITION_TIMEOUT, local_position.xy_valid && local_eph_good, &(status.condition_local_position_valid), &status_changed);
  

  ?

  void check_valid(hrt_abstime timestamp, hrt_abstime timeout, bool valid_in, bool *valid_out, bool *changed)
  // timestamp = local_position.timestamp
  // timeout = POSITION_TIMEOUT
  // valid_in = local_position.xy_valid && local_eph_good  判斷位置精度是否滿足
  // valid_out = &(status.condition_local_position_valid)
  // changed = &status_changed
  {
      hrt_abstime t = hrt_absolute_time();
      bool valid_new = (t < timestamp + timeout && t > timeout && valid_in);  // 判斷是否超時 和 xy_valid 與 local_eph_good 是否同時有效
      if (*valid_out != valid_new) {
          *valid_out = valid_new;   // 對 condition_local_position_valid 進行賦值 = true
          *changed = true;   // 對 status_changed 進行賦值
      }
  }
  

  ?