The main issue is, you either assume a scenery can be sloped, or you assume it's not, and either way you'll have issues because:
- If we assume every scenery can have some kind of slope, which is what we should, since every airport DOES have some kind of slope, however gentle it might, and in real life usually is *very* gentle, since trying to do a Pushback on an sloped terrain would be extremely dangerous, especially with a Towbar, so it's very like that, where Pushback is allowed, the terrain there should be mostly flat in real life, and if there are slopes, they should start after the standard pushback end positions. So, while pushing, GSX keeps the airplane and the tow truck at 0 altitude above ground, so both can follow the (gentle) slope correctly.
Of course, if the scenery has a much significant slope, or a bump, or possibly even a "hole" in the terrain, both vehicles will have an hard time following it, while being pushed at 0 ground level, not least because the variable that holds the altitude above ground is NOT updated exactly in realtime at each frame and following precisely the terrain, there's some lag on it, and the resolution is not enough, that's why it might break, because we need to read it and write it from Simconnnect.
Default systems in the simulator, like the default pushback, are not suffering from these issues, because they don't use Simconnect, so they are not affected by any lag or lack of resolution of the variable used to hold the current ground altitude.
- If we assume a scenery is flat, like we did in FSX/P3D, when most sceneries *were* effectively flat, since sloped airports came out only with P3D V5, (but nobody really use it, since it's way more complex to do than in MSFS and there are no terraforming tools in the SDK), it would cause a bigger problem because, while we might not suffer from having to get the ground altitude with some lag or lack of precision, because we could just move the two vehicles using a "flat" absolute altitude, if the altitude changed, even slightly, during the pushback route, you'll see the tow truck going progressively below ground, if the ground altitude increased, or floating above ground if the altitude decreased.
This will happen EVERYWHERE, because even airports without a visible slope ARE in fact sloped, but if the slope is smooth, GSX won't have any issues following it, but if we moved by assuming it's flat, even a very smooth altitude difference, would be very visible over a distance.
That's why, between having to choose something that would cause problems *everywhere* ( if we assumed the pushback area is flat ), it's best to use the solution that works in most places, except those few stops where the scenery is not how's supposed to be, since these can possibly fixed at the scenery level, as they should, because the kind of slope that would cause a problem to GSX Pushback, would probably prevent to even try a Pushback, if it really happened in real life.
