This is my testing setup, using the RaspberryPI as the serial to mavlink gateway.
The Jevois is doing object tracking on the red ball and sends coordinates to serial port
RasberryPi2 is running DroneKit Python, reading x-y coordinates , scale & adjust and send message Landing Target over to the Simulator (SITL) running on the left computer using serial ports (you can see the FTDI flashing between the screen and computer)
SITL is a fully compliant Ardupilot Simulator, so it is configure to run precision Loiter and Landing. I can takeoff and control the fly direction by moving the Red Ball on front of camera.
The simulator also output Mavlink to UDP so that the computer at the right that is running the Analyse Widget from QGroundControl. It is reading the Landing Target x & y message and graph the Red Ball movement being detected by JeVois.
Next step, is obviously to use the Mavlink Module and discarding the RaspBerry Pi.