Originally published on https://www.justflight.com/articles/developers-diary-traffic-global-for-xplane-11
Hello! Welcome to the dev diary for Traffic Global for X-Plane – TGXP to friends. I’m going to be talking about how this came about, what it does, what it doesn’t do, why, and quite a lot of what goes into making it work. There’s going to be a certain amount of techy background detail – hey, it’s a dev diary – but I want this to be open to anyone with a little interest in what goes into making your sim a nicer place to be.
So where did this all come
from? Seems like a good place to start. For the last couple of years I’d been
doing contract work for Dovetail Games on Flight Sim World, mainly on the
missions side – they licensed my FSX Mission Editor and commissioned a load of
updates both to that and the sim’s mission system – but eventually also in lots
of other parts of the sim. Sadly Dovetail stopped work on that in early 2018 as
I’m sure you know, and I was looking out for something else to fill the gap.
Enter the nice people at Just Flight who said they had something in mind. Yep,
Traffic Global for X-Plane.
As it happens, one of the areas I’d worked on for Dovetail FSW was traffic, adding a lot more GA flights to smaller airfields, so I had a good idea how that side of things worked. Short version: a list of flights comes from a file, matching planes come from other files, these in turn are matched against airports and parking availability and as if by magic, you get planes flying planned routes in the sim.
Of course, anyone who’s seen The Wizard of Oz knows that “magic” depends on somebody in the background doing a damn fine impression of a drug-crazed tapdancing octopus trying to get all the levers to be pulled at the right time.
For a traffic add-on there are in fact two tapdancing octopi: one preparing all the data, and another using it. Just preparing the data – making sure that all the flights work properly, pairing with a simulated world that doesn’t match the real one, providing all the necessary models – is an enormous task. The other octopus, at least for Prepar3D/FSX/FSW (I’m going to use these interchangeably), is provided by the simulator. Feed it the right data, it’ll fly the planes around.
Not so for X-Plane.
It used to be the case that X-Plane would move planes around for you to some extent if you controlled their autopilot settings. That’s fine for going from A to B, but what about landing? Taxying to parking? Circuit patterns? As it happens, none of that was relevant because this whole facility was removed some time ago.
Can I just feed it some kind of traffic database, like P3D uses? Nope. Oh, and X-Plane only supports a maximum of 20 non-player planes too, even if the autopilot trick still worked, which it doesn’t. If this sounds like I’m beating up X-Plane, bear with me, I’m not! Those 20 planes that can be controlled from outside the sim are really meant for multiplayer rather than AI traffic, so in fact both the small number and the removal of the autopilot kind of makes sense. It does leave you with only one option though: you can have any number of planes added to the sim using a different approach if you control them yourself. Entirely yourself. 60 times a second, you need to tell X-Plane where your planes are, how they’re oriented and animated. For potentially hundreds of planes in the player’s local area from tens of thousands around the world.
Okay then. This is going to take some planning.