That's totally un-necessary, unless the planes fly artificially low over the terrain, or you have a reeeeeally huge building (in which case, there are methods you could use to generate a proper avoidance behavior that are still superior). World Builder stuff makes a lot of this thread seem rather quaint. The only real problem remaining is that Units attempt to shoot through the buildings, but meh, they did that in OTA, too!Couldn't the approach taken with the original treemap (that is, the buildings just mask an invincible piece of terrain in behind them) work for buildings? Obviously, you wouldn't be able to have skyscrapers, but a Paris-like city of midrise buildings should be doable, right? Then they'd have a near-proper collision box and planes wouldn't fly through them.
Not to mention it would be a serious pain in the ass to make a map like that, and that planes' behavior would be bizarre and counter-intuitive. Planes don't see the terrain ahead of them, they are strictly responding to the terrain they're over right now. It's not a very good solution, frankly.