code: def set_roi(location):
      
      # create the MAV_CMD_DO_SET_ROI command
      msg = vehicle.message_factory.command_long_encode(
          0, 0,    # target system, target component
          mavutil.mavlink.MAV_CMD_DO_SET_ROI, #command
          0, #confirmation
          0, 0, 0, 0, #params 1-4
          location.lat,
          location.lon,
          location.alt
          )
      # send command to vehicle
      vehicle.send_mavlink(msg)
docs: Send MAV_CMD_DO_SET_ROI message to point camera gimbal at a 
      specified region of interest (LocationGlobal).
      The vehicle may also turn to face the ROI.
  
      For more information see: 
      http://copter.ardupilot.com/common-mavlink-mission-command-messages-mav_cmd/#mav_cmd_do_set_roi