Understanding GTR2 weather change and track surface

MJQT · Dec 18, 2021

Decided to hop in for a few minutes and do a quick race in GTR2 HQ Porsches the other day. I always leave the weather on changeable so that I sometimes get rain, and so the game gives varying surface and air temperatures that aren't always 20 degrees Celsius.

So I did, at Monza (although I usually have more diverse tastes than a "white bread" choice like that haha). Anyway, it was pouring rain at the start.

Then the rain suddenly stopped, two laps in. Wipers disappeared, as you would expect, because the rain texture on the windscreen was gone. Was really abrupt, caught me off guard, but hey, it's fine. The physics also seemed to abruptly change to a grippier feeling, although I can't say for sure. However, for a lap or so it seemed that there was still rain on the track in some places, because I could see AI cars' tire tracks on the track in front of me, but not everywhere e.g. seemingly not on the racing line. I found this really interesting.

Then I noticed some AI cars were immediately pitting in. I was momentarily confused, then realized this must be for dry tyres. I decided to stay out at first, because it was a sprint race, and I noticed on the LCD that my (wet) tyres were heating up like crazy. As they should, on a dry track! So I pitted in and got dry tyres like everyone else and carried on until the end. As far as I could tell, my new slick tyres behaved like normal slick tyres on a dry surface.

This leads me to wonder... does GTR2 simulate a dynamic racing surface drying out after rainfall ends? If so, how? Or does it immediately dry up the moment the rain stops? Would love to learn more about this.

Shovas · Dec 18, 2021

I thought it just did wet-dry lines by varying grip levels but it looks like it might be more advanced:

From 2006:

"It's named after the LiveTrack function, which has itself been upgraded to include rain on some parts of the circuit while it's dry on others, the proper emergence of an extra-grippy 'dry' line and the temperature effects of the new 24-hour sun cycle."

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From 2006:

" Long jets of water, spectacular reflections on wet tarmac and an upgraded "Live Track Technology" with different self-drying track sections create a realistic race feeling in GTR 2 even with bad weather."

Weather Forecast: Heavy Rainfall in "GTR 2 – FIA GT Racing Game"

Darmstadt/Vara, Sweden, 7th April 2006: Developer Simbin Development and Publisher 10TACLE STUDIOS are today disclosing…

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From 2018:

"It was in fact implementing the very first iteration of the LiveTrack technology that has now come into its third iteration in Project Cars 2. This means that the racing line gets progressively more rubbered as time goes on, while outside of the ideal line, marbles will accumulate and will be present, both graphically and physically, for the player to deal with. Rain, however, while making the track more slippery, will also wash down the surface, playing still another factor to take into account while planning your race."

https://www.racedepartment.com/threads/best-of-simracing-mods-%E2%80%9Cpower-and-glory%E2%80%9D-for-gtr2.152077/page-5

Unknown date but seems early:

"The superb LiveTrack system means that dirt accumulates on the track surface and should it rain, heavily-used areas of the track will dry out first"

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Deleted member 13397 · Dec 19, 2021

basicly, the track has to variables,
onpath wet and offpath wet
i am not sure if this is a track width constant but works in GTR2 & RACE07

and rain and temp / clouds seems to have an impact on them

races can also start with a wet track (check weather file)

there might be another variable like grip factor, but did not investigate this yet

The Iron Wolf · Dec 19, 2021

MJQT said:
Then the rain suddenly stopped, two laps in. Wipers disappeared, as you would expect, because the rain texture on the windscreen was gone. Was really abrupt, caught me off guard, but hey, it's fine.

In case you didn't know, CC plugin supports wipers that don't disappear and are button controllable. You can see how they look with all hq and png cars thanks to gtr233. I also share car wiper patches at trackaholics

Bjarne Hansen · Dec 20, 2021

MJQT said:
This leads me to wonder... does GTR2 simulate a dynamic racing surface drying out after rainfall ends? If so, how? Or does it immediately dry up the moment the rain stops? Would love to learn more about this.

As Mucho states there are two different wetness.
Wetness on the racing line will dry out first while off the race line dries out a little slower.
While we are not 100% it looks like the drying out are 'just' based on time and temperature not the amount of cars driving.
So in some ways it is dynamic

You can make abrupt weather changes with a weather.txt file.
In general the random weather changes are very realistic gradient.

In both Gtr2 and Race 07 it can be hard visual to judge how much it is raining and how wet the track are at any given moment.

And your rain tires will get hotter and wear down faster on a dry track if you drive aggressive.
So while it all might be part scripted it is done very well and makes us users fell it is dynamic and very realistic.

MJQT · Dec 20, 2021

Thanks Shovas, Iron Wolf, mucho, and Bjarne for the info! Interesting to know about how the dynamic track works.

Bjarne Hansen said:
You can make abrupt weather changes with a weather.txt file.
In general the random weather changes are very realistic gradient.

That's what surprised me, because the seemingly abrupt weather change came directly out of the game's "changeable weather" setting. Must have just been a RNG providing an unusual experience. Only one or two laps after heavy rain stopping, the track was seemingly completely dry, as I could run on slicks as if the track was fully dry. I don't think this is realistic, but I'm honestly not 100% sure. Anyway, with a more gradual gradient (whether auto-generated by the game or in a custom weather.txt I created) would the track dry slower? Or are there track variables that, if changed, could make this happen?

The Iron Wolf said:
In case you didn't know, CC plugin supports wipers that don't disappear and are button controllable. You can see how they look with all hq and png cars thanks to gtr233. I also share car wiper patches at trackaholics

Didn't know about the CC patch adding that change (and hadn't yet tried out CC with GTR2). Will have to try it out!

Shovas · Mar 19, 2024

Bjarne Hansen said:
While we are not 100% it looks like the drying out are 'just' based on time and temperature not the amount of cars driving.
So in some ways it is dynamic

I've been working on weather, had some problems and was searching for stuff on drying tracks and found this. As it turns out, I've just collected some data on this scenario:

Code:

- Track wetness floods dynamically based on Conditions and un-floods dynamically

  - Dry->Wet->Flooded->Wet->Dry then:

      - 0 AI 40min still flooded, ...

      - 1 AI 40min still flooded, ...

      - 10 AI 30min flooded->wet, ...

      - 20 AI 20min flooded->wet, ...

      - 29 AI 15min to wet, never dry

^ None of these got to damp either

This was a vanilla 90min Practice 1 at Donington GP 2004. I just stayed in the garage and time accelerated so the AI ran laps.

On that note, I'm having trouble constructing a weather file where the track dries out completely.

So far, I've only been able to observe drying one level lower, ie. Flooded > Wet or Wet > Damp, but never Flooded > Wet > Damp > Dry or Wet > Damp > Dry.

Anyone have ideas?

Crimson_764 · Mar 19, 2024

Shovas said:
I've been working on weather, had some problems and was searching for stuff on drying tracks and found this. As it turns out, I've just collected some data on this scenario:

Code:

- Track wetness floods dynamically based on Conditions and un-floods dynamically - Dry->Wet->Flooded->Wet->Dry then: - 0 AI 40min still flooded, ... - 1 AI 40min still flooded, ... - 10 AI 30min flooded->wet, ... - 20 AI 20min flooded->wet, ... - 29 AI 15min to wet, never dry

^ None of these got to damp either

This was a vanilla 90min Practice 1 at Donington GP 2004. I just stayed in the garage and time accelerated so the AI ran laps.

On that note, I'm having trouble constructing a weather file where the track dries out completely.

So far, I've only been able to observe drying one level lower, ie. Flooded > Wet or Wet > Damp, but never Flooded > Wet > Damp > Dry or Wet > Damp > Dry.

Anyone have ideas?

I've been able to do races where the weather has gone through each of the stages. For example when I did the 2003 version of the Spa 24, I took the weather file from GTR 1, and I observed that it started dry, and then after about 2h it got progressively wetter through each of the track conditions until eventually getting to Flooded (Aquaplaning {AP} shown on XD).It then stayed like this for a while until it began to dry again with the rain stopping and the track eventually getting to the dry state once again. So I can confirm it does indeed work as intended, you just have to make sure the weather lines up properly and also from mods that I've seen that can change it, it doesn't do time-scaled weather from what I remember.

Shovas · Mar 19, 2024

I'll have to try again with a longer session then, I think. I only gave it the 90min practice to dry out so far.

Shovas · Mar 20, 2024

Finally got to a dry track in a 600min practice with 29 AI (they stop lapping around 2h, though) and the track got dry in ~5.5hrs (275:00)

It seems to take overly long to dry out for a clear, sunny day?

Code:

- Track wetness floods dynamically based on Conditions and un-floods dynamically
  - Dry->damp_>wet->flooded—>wet->damp-dry:
    - 20C Amb 30C Track
    - 90min Practice:
      - 0 AI 40min still flooded, ...
      - 1 AI 40min still flooded, ...
      - 10 AI 30min flooded->wet, ...
      - 20 AI 20min flooded->wet, ...
      - 29 AI 15min flooded->wet, never dry
    - 180min Practice:
      - Damp ~65:00 (-115min)
    - 300min practice
      - Wet 285:00 (-15min)
      - Damp 185:00 (-115min)
    - 600min practice 1
      - Cars stop lapping 485:00 (-115min)
      - Dry ~275:00 (-325min) 
    - 600min practice
      - 29 AI
      - Cars stop lapping 485:00 (-115min)
      - Wet 585:00 (-15min)
      - Damp 486:00 (-114min)
      - Dry ~275:00 (-325min)
    - 600min practice 2
      - 3 AI
      - Cars stop lapping 515:00 (-85min)
      - Wet 548:00 (-52min)
      - Damp 472:00 (-128min)
      - Dry 253:00 (-347min)
    - 600min practice 3
      - 0 AI
      - Cars stop lapping  N/A
      - Wet 515:00 (-85min)
      - Damp 393:00 (-207min)
      - Dry 248:00 (-352min)

This was with a simple, minimal, controlled weather.txt:

Code:

Weather
{
 Practice1
 {
  Conditions=0.00
  Minute=1.00
  {
   Conditions=0.00
  }
  Minute=2.00
  {
   Conditions=62.00
  }
  Minute=3.00
  {
   Conditions=91.00
  }
  Minute=4.00
  {
   Conditions=100.00
  }
  Minute=5.00
  {
   Conditions=91.00
  }
  Minute=6.00
  {
   Conditions=62.00
  }
  Minute=7.00
  {
   Conditions=50.00
  }
  Minute=15.00
  {
   Conditions=40.00
  }
  Minute=30.00
  {
   Conditions=30.00
  }
  Minute=45.00
  {
   Conditions=20.00
  }
  Minute=60.00
  {
   Conditions=10.00
  }
  Minute=70.00
  {
   Conditions=0.00
  }
  Minute=80.00
  {
   Conditions=0.00
  }
}

Jempy · Mar 20, 2024

Without time acceleration and at 20° ambient .... IRL if it rains in the early morning ( living near Spa at a +- 20 km distance but at a slightly lower altitude ) with the back of my house at full south ( and sun present at the left side round 10:30 am ..... the pavement at the back will only be fully dry without any water leftover round 12:00 .... so your 5,5 hours finally look .... rather realistic.

Maybe adding the temperatures at the different stages of your test might prove a bit more as it may differ from track to track according to their location.

NB: just noticed everything was done in practice ( else said not all cars on track all the time ) .... should it remain the same in race session ?

Shovas · Mar 21, 2024

Jempy said:
Without time acceleration and at 20° ambient .... IRL if it rains in the early morning ( living near Spa at a +- 20 km distance but at a slightly lower altitude ) with the back of my house at full south ( and sun present at the left side round 10:30 am ..... the pavement at the back will only be fully dry without any water leftover round 12:00 .... so your 5,5 hours finally look .... rather realistic.

Maybe adding the temperatures at the different stages of your test might prove a bit more as it may differ from track to track according to their location.

NB: just noticed everything was done in practice ( else said not all cars on track all the time ) .... should it remain the same in race session ?

Good data points, thank you.

I did collect data at 0-50C ambient with +10C increments and I definitely confirmed higher temperature dries out faster with no AI on the track but its effect is virtually eliminated when their are AI on the track.

For most of practice, I'd say 90% of the cars were on the track at any one time, so I have my doubts if that varies by session.

I've been trying to figure out what Time Scaled Weather does exactly. In your experience, what does it do?

Data for drying out based on temperature:

Code:

- Flooded Time to Wet by AI Count and Temperature
  - Starts Flooded, and immediately dries out at Minute=0.10{}
  - 600min Practice
    - 0 AI
      - Wet 516 0C
      - Wet 541 10C
       -  Wet 552 20C
      - Wet 564 30C
      - Wet 568 40C
      - Wet 573 50C
    - 10 AI
      - Wet 584 0C
      - Wet 584 10C
      - Wet 586 20C
      - Wet 587 30C
      - Wet 587 40C
      - Wet 588 50C
    - 20 AI
      - Wet 588 0C
      - Wet 587 10C
      - Wet 587 20C
      - Wet 588 30C
      - Wet 588 40C
      - Wet 589 50C
    - 29 AI
      - Wet 590 0C
      - Wet 590 10C
      - Wet 591 20C
      - Wet 591 30C
      - Wet 591 40C
      - Wet 591 50C

Jempy · Mar 21, 2024

In fact, I don't know what Time Scaled Weather does practically.

I only can guess it is linked to time acceleration rate and also the fact that one can manually accelerate time at Practice and Qualifying sessions....

.... meaning logically that if one of those 2 functions are used .... the time of the weather per minute in the weather.txt will also be accelerated at the same ( or +- anyway) rate of the Time acceleration or the one used by the player in the session times.

As the weather.txt file created by the game is not ReadOnly its evolution might be changed by the game when time is accelerated.

NB: but in this case, I cannot understand why a personal weather.txt file Read Only .... makes mandatory to uncheck this "Time Scaled Weather" feature !?? .... Read Only doesn't give the possibility of modifying the file !????

Another question:
Is the track grip following perfectly the graphical looks of track ( less or more water ) or might it be totally quicker ?? ..... is it possible to measure the grip in place of wet ? or compare both ?

The Iron Wolf · Mar 21, 2024

Jempy said:
Another question:
Is the track grip following perfectly the graphical looks of track ( less or more water ) or might it be totally quicker ?? ..... is it possible to measure the grip in place of wet ? or compare both ?

I never looked at tire grip, but there might be something exposed via rF1 Plugin API. You can explore and plot values very easily using SimHub.

There's a value onpathWetness and offpathWetness (names may not be accurate), but I don't remember if per wheel grip value is exposed. Check out raw properties in SimHub if interested. And don't forget Player is not the same as AI in GTR2 - different physics and I am pretty sure all per wheel stuff is player only. SimHub supports recording trace, so it's easy to capture your driving then analyze data later.

Shovas · Mar 23, 2024

Here's my notes experimenting with Time Scaled Weather

tl;dr
- Time Scaled Weather is only(?) for 24h races compressed into a shorter session length
- Time Scaled Weather's purpose is to reduce the frequency and magnitude of weather changes that would occur if blindly compressed into a shorter time frame so that it feels more natural
- No evidence it is used to scale up a short weather.txt to a longer time frame (ex. it is not used to scale up a 30min weather.txt to 24 hours)
- 24h weather.txt files only have 180 Minute{} blocks. I have never seen it loop or repeat in other sessions so I can only assume a 24h session loops it or does actually stretch out the Minute{}s over the longer session length (less likely because it's more complicated?).

Code:

Real Time Weather and Time Scaled Weather:
- Time Scaled Weather does not seem to be related to Daylight Acceleration
- Time Scaled Weather does not seem to be have any effect for custom weather.txt files
  ^ This implies that Time Scaled Weather is for game generated weather files
  ^ Which means it's not the weather.txt Minute{}s being Time Scaled but the game weather generation algorithm scaling based on session length.
  ^ This probably means that a few weather events play out over longer rather than the game generating many weather events to fill in the time
  ^ Should be able to confirm by checking weather.txt for a 24h race with Real Time vs Time Scaled Weather
- For 24h Race Game Generated Weather Files
  - Real Time weather.txt has many more Minute{}s, a much more granular Minute{} progression, in steps of 1-2 minutes each
  - Time Scaled weather.txt has much less Minute{}s, a broader Minute{} progression, in steps of ~10 minutes each
  - Real Time weather.txt has more variability in Conditions (ex. 0-40)
  - Time Scaled weather.txt has less variability in Conditions (ex. 65-74)
  - AmbientTemp seems to have a +/- 10C range for both
- Conclusion:
  - Time Scaled Weather's purpose is to simulate longer weather patterns in shortened sessions
  - Nothing seems to suggest it allows for scaling up limited weather.txt Minute{}s to sessions with more minutes
  - It seems like Time Scaled Weather is only for 24H races
  - 24H generated weather.txt Race Minute{}s still only represent 180 Minutes so it seems the game is internally stretching that over the entire period or possibly looping it
    ^ Neither stretching or looping behaviour is seen in regular race sessions: In regular races, it loops through the Minute{}s until they're done and does not loop, stretch, or condense them based on the session length.
  - Used ChatGPT to see if it agrees and it agreed: https://chat.openai.com/c/a3af0967-5df1-45e9-87a9-cdbf1789c4bd