code: def add_latlonalt(self, lat, lon, altitude, terrain_alt=False):
          '''add a point via latitude/longitude/altitude'''
          if terrain_alt:
              frame = mavutil.mavlink.MAV_FRAME_GLOBAL_TERRAIN_ALT
          else:
              frame = mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT
          p = mavutil.mavlink.MAVLink_mission_item_message(self.target_system,
                                                           self.target_component,
                                                           0,
                                                           frame,
                                                           mavutil.mavlink.MAV_CMD_NAV_WAYPOINT,
                                                           0, 0, 0, 0, 0, 0,
                                                           lat, lon, altitude)
          self.add(pf add_latlonalt(self, lat, lon, altitude, terrain_alt=False):
          '''add a point via latitude/longitude/altitude'''
          if terrain_alt:
              frame = mavutil.mavlink.MAV_FRAME_GLOBAL_TERRAIN_ALT
          else:
              frame = mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT
          p = mavutil.mavlink.MAVLink_mission_item_message(self.target_system,
                                                           self.target_component,
                                                           0,
                                                           frame,
                                                           mavutil.mavlink.MAV_CMD_NAV_WAYPOINT,
                                                           0, 0, 0, 0, 0, 0,
                                                           lat, lon, altitude)
          self.add(p)
docs: add a point via latitude/longitude/altitude