Flightgear visualization doesn't work in Ubuntu Focal

[Jaeyoung-Lim]

Description of issue
Flightgear visualization is not working on Ubuntu Focal and only displays the vehicle in a empty ocean. When the vehicle is in flight, the vehicle does not move even when PX4 is in flight.

When looking closer, I noticed the following error:

   11.00 [ALRT]:io         Error: version mismatch in FGNetNativeGUI2Props()
   11.00 [ALRT]:io              read 402653184 need 8
   11.00 [ALRT]:io              Need to upgrade net_fdm.hxx and recompile.

Posted Issue: JSBSim-Team/jsbsim#325

[mvacanti]

@Jaeyoung-Lim my attempt at the two issues:

1. The Ocean issue is likely caused by the fact that the default installation of FlightGear only includes a very small portion of the global scenery. Try downloading and installing the scenery for your particular location using instructions here: FlightGear Scenery

2. The lack of FlightGear update is likely caused by an incorrectly configured FlightGear input configuration in sitl_run.sh. Try starting FlightGear first using the GUI launcher with the following settings:
   
   Then launch PX4 and the jsbsim_bridge (may have to modify the FlightGear launch in sitl_run.sh)

As a note I am running my setup on Ubuntu Focal, FlightGear 2020.1, and a Docker container (also Focal) for PX4 and the jsbsim_bridge. I installed FlightGear using the instructions here.