How large can track maps be?

Bram

Founder & Administrator
Staff
Premium
Something I have been wondering about for some time is the limit on track sizes.

Personally my ultimate "simracing" game would be a mix between the physics and looks of Assetto Corsa and a track the size of an island as we saw in Test Drive Unlimited and just do some free driving with friends in cool looking cars, hang out on parking lots, do a little donut here and there and drive :D

Would such a ridiculously large track map be an option for AC? I mean the size of the Nordschleife will be significant as well.
 
OK, i know absolutely nothing about building a track map but this is a great idea and would be great fun to drive on:) Maybe you really smart guys can work a deal with Google Maps and use their info to do a big map rendered on the fly (yes, of course I own a super computer). Well, if that doesn't work, since I live in the US desert area with a lot of mountain roads too, then I am willing to take a zillion pictures of a 16x16km area and have it made into a map:D
 
What does "floating point number" means? (sorry track building noob here :D)
Here is a simple rebus to help understand the subject:
260px-A_Boat_in_the_Nile_River.JPG
220px-Mesa_Verde_spear_and_knife.jpg
0.jpg


The computer throws a pointy spear at a number... but if it has to throw it 16km it's not as precise as if it only had to throw it 100m. So if the tracks are too big then the spears miss and then your car falls down go boom.
 
I'm a programmer, but not a 3D modelling expert. But it seems odd to me that the area size (16x16) would be the limit. From my point of view (low level hardware-adjacent programming) it would make more sense if the limitation was based on available memory (RAM and GPU), in which case it should be track length rather than area span that should set the limit? Either way, I'm sure there are a thousand reasons why I'm off in my reasoning. :)
 
For a more technical response, it's because vertex positions of models are stored as floating point numbers, which only have so much precision. For a 32bit float, you have ~7 decimal digits of precision. So, say, 2.135506m, or 0.001936722m, or 8062.536m - and the farther away from the 0 coordinate you are, the less precision there is.

The 16x16km limit is just to make sure that numbers stay reasonable - if you're 8000m from the origin, you only have millimetre accuracy in locating any vertex. And that's just the first step - errors have a habit of accumulating. 0.5 mm here, plus another each time you do any math to it (moving the car model, projecting it onto the screen, etc.) and you don't want it to add up to a visible difference or stuff starts getting shaky, as from frame to frame some of the errors will be in different directions.

I wouldn't expect it to be a hard limit, just that things get progressively worse far away, so it's advisable to stay well within the bounds that behave sensibly. If you expect the road to be smooth and it's bouncing up and down several centimetres, that is enough to have an impact on handling...
 
Here is a simple rebus to help understand the subject:
260px-A_Boat_in_the_Nile_River.JPG
220px-Mesa_Verde_spear_and_knife.jpg
0.jpg


The computer throws a pointy spear at a number... but if it has to throw it 16km it's not as precise as if it only had to throw it 100m. So if the tracks are too big then the spears miss and then your car falls down go boom.

Hahahagahaha, I can't believe someone went to the effort of disliking your post! :D
 
Just to get things a bit into perspective for myself, how large were the Ibiza and Hawaii maps in TDU2? Bigger than 16x16 as they represented the real island?
 

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