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iRacing: A Closer Look at the New Dynamic Track Surface Model

Paul Jeffrey

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iRacing Track Surface Update.jpg

iRacing have recently revealed interesting new information about the upcoming dynamic track surface model set to arrive to the sim very soon.


Having already introduced a basic first pass at dynamic surface modelling to the simulation, aimed mostly at adding layers of realism for the recent move towards simulating loose surface dirt series racing, iRacing Senior Software Engineer Dan Garrison has shared some interesting insights into what the new tyre surface model is expected deliver to fans of the title:

"The initial implementation of the dynamic track model featured the server maintaining surface temperatures all over the racetrack, and sending this information to the clients. Temperature from one spot to another would vary according to things like the albedo of the surface, the orientation of the surface with respect to the sun, the intensity of solar radiation as a function of the solar elevation angle, shadows, clouds, and finally from the influence of cars. Areas of inactivity in the shadow would be cool, areas in the sun would be warm, and anywhere cars were dumping heat from engines and tires would warm up further. This gave us a model that would actively respond to many of the real-life factors that one would encounter, and provide a range of conditions to deal with as a race engineer and/or driver.

When the dynamic track was first released, the weather in the sim was rather static: air temperature and wind might shift a little if the settings allowed such, but the sun did not move and neither did the clouds. This meant that it was possible to calculate the equilibrium temperature of an area on the ground, as it was simply that temperature which created a perfect balance of solar energy being added and the energy lost by conduction and convection. Since the weather was known and the sky was static, if no one was driving on the track the temperatures would remain essentially unchanged save for some small changes that would roughly correspond to changes in the ambient air temperature.

Once the sun and the clouds started moving, however, one of the major shortcomings of this model became apparent: namely, that the server only kept track of the temperature on the top surface. As a result, as the sun sets or if a cloud comes by, the track temperature cooled rapidly with the incoming solar energy gone. Fluctuation in the rate of heat loss was introduced, as a function of time of year and time of day, to try to account for what would be happening under the surface. However it was a rough approximation of what was really going on, and the overall variation in the cooling rate was kept relatively small in order to avoid strange behavior.

The new implementation of the dynamic track addresses this by maintaining temperature in multiple layers under the ground, which means that the surface temperature will behave more realistically. With the new model, heat that is stored in the layers below from hours of sunlight will work its way back up and warm the surface. Similarly, built-up heat from cars will last longer if a lot of laps have been driven instead of just a handful. The end result compared to the original model is that temperatures will typically be cooler in the morning and early afternoon, but warmer in the late afternoon. But in general the multi-layer approach will stabilize the temperature on the surface to some degree, in that it will change more slowly in most circumstances.

Put another way, the layers allow a realistic recording of history that the old model simply could not reflect. Think especially about a hot day that has a hint of a late-afternoon monsoon that is only a very short, mild rain shower: in the old model, the track temperature would have plummeted and stayed cold, even after all the water was gone. With the new model, the heat that was stored in the lower layers beforehand can slowly return to the surface and allow it to regain some of the lost temperature, even if the skies stay cloudy. In fact it was working through this type of scenario that motivated the update to the dynamic track model.

One of the problems that must to be solved in this approach is the initialization of the temperature in the various layers. If the layers are set up incorrectly, temperature at the surface will drift and fluctuate unrealistically until things eventually settle towards the correct temperatures. To handle this, the server creates a number of samples for each type of material found at the track, and uses an empirical formula to estimate the temperature in each layer that takes into account time of year, the thermal conductivity of the material, and the depth of each sample point where temperature is being tracked. It then goes one step further, and simulates the weather for a few days before the event actually starts, updating the temperature profile of each sample. This ensures that the layers will be at the proper temperatures given the conditions and will behave correctly once the first session starts.

It then continues to move forward in time and periodically storing additional data points, so that any additional sessions that start after a delay will also begin with appropriate temperatures at all depths. If an event has a two-hour practice scheduled in the morning, qualifying that afternoon and a race the following day, the temperature model will handle that because it has run the weather and modeled the changes already. When a session starts and a piece of the ground needs to know its initial set of temperatures, it finds the data for its material type and the current time, and uses its orientation on the ground to choose and interpolate between a few saved samples.

This helps address a second shortcoming of the original model that became apparent with the moving sky: at the start of a session, if a fair amount of time had elapsed since the end of the previous one, the server simply looked at the amount of solar energy coming in at that time in order to calculate the starting temperature. If the sun was behind a cloud, it did not attempt to guess at how long or how often it had been behind the cloud, nor did it simulate the conditions leading up to the session. As such, in this case the track would usually start off unrealistically cool, as if the cloud was there all day. In the new model, if the sun was out most of the time leading up to that moment, that will be captured and the track will still be hot but cooling off.

The new model also features a much better interaction between water and temperature, as the evaporation and removal of heat from that process is calculated more accurately than before. A dirt track in constant shade, perhaps say in Oklahoma, will typically have a track temperature below that of the surrounding air because of the heat lost due to evaporation. Of course the rate of evaporation varies depending upon the temperature of the surface and the air, the humidity, the wind, and the availability of “free” water at the surface. On a chilly, humid, windless day you would expect the track temperature to be close to the air temp, while on a hot, dry, windy day you might expect several degrees of difference between the air and the ground. The upgrade to the dynamic track provides this behavior as a natural consequence of the improved evaporation model.

Although these changes to the track model are inspired by the anticipation of rain in the sim, hopefully it is clear that the update is beneficial across the board. By modeling heat transfer between the surface and the ground beneath, the reaction of the track temperature due to different events is influenced by what has already occurred. As such, the surface temperature may be relatively persistent or variable depending upon the history that is essentially stored in the layers below. Finally, by running the weather forward during initialization and recording the results, the server is better prepared to handle session transitions that can include large gaps in time and start the track in the appropriate state.

Link to original article HERE.

All sounds very exciting, and remarkably detailed... looking forward to giving it a try when it releases in the very near future.

Stay up to date with the latest news, check out the iRacing sub forum here at RaceDepartment!

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You don't have to believe if you don't want to. You live in a free country, I assume :)

I do and assuming you do, too, it would be nice if you replied to the content of what I was purporting. In a real race car, we can feel the deterioration of grip from tire wear. Depending on the series and the tires used, this might be incredibly subtle. We can feel the effect of dropping a tire off the track or going into the marbles. Both of these represent colossally huge losses of grip relative to a brand new/clean tire.

If the banked corner on an oval was chequered with shady and sunny sections, could we feel the grip rising and lowering as we passed over these in a real race car? Unlikely. Partly that's because the underlying construction of the road would spread the temperature effects (as iRacing has now programmed) with the impact that the changes in temperature would not be sharp-edged like the shadows themselves. The whole area might blend into something halfway between the sunny and totally shaded areas. Could we feel the difference between the totally sunny area and the totally shaded area? Maybe. But it represents a dramatically lesser impact on grip than either wear or marbles/dirt.

So do you believe as you are rounding that corner with the shady blocks interspersed with the sunny blocks, you are going to be able to detect the minuscule alternating change in grip? I am suggesting that not even an F1 team's sims can do that. Therefore, modifying track temperature by a much less sophisticated procedure, across much larger sections of track, would be more than adequate given that the rest of the sim and our equipment (even high-end DD wheels) is incapable of distinguishing the differences.

Note that for water/rain and puddles, the opposite is true. The presence of standing water or the impact of heavy rain will be able to felt even with modest equipment and therefore would warrant a sophisticated approach to calculating water on the surface, water flow, standing water and the impact of temperature, sun, wind and vehicles on the drying/evaporation of the water.

Just my opinion...but there are lots of examples of sims getting ahead of themselves with complex calculations that have little to no value in the real world (including real world racing. This is one of them. There are other things that I would personally prefer iRacing spend their limited dev time on long ahead of this feature.
 
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Well you see. RD has a relatively small user base and the admin must have a good faith in the maturity of the average users, so they let you know who pressed that disagree button. Yet I can still smell the conflict in the air.

Imagine YouTube lets everyone know who thumbs down everyone's videos/comments, etc. I guess I will see riot on the streets tomorrow, and the US might decompose from the inside.:whistling:
 
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Sounds great, when comes finally a good tire model? Never?

Gotta love how you pop into every thread and just completely off-topic bash the tire model. Damage model? But the tires! Surface model? But the tires! It's so pointless.

By the way, what do you base your opinion that iR has the worst tire model (quite a bold statement) on? Do you have any experience pushing a racecar to its limit in real life? Or do you just base it on street driving, what you think it 'should' feel like and what other people say?
 

M-Bimmer

WhAt GoEs ArOuNd CoMeS ArOuNd
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this is just hate on Iracing because when something is as good as Iracing it always have a lot of haters who cant afford it
Why assume? Quite sure the majority (if not all) here can afford it so logically speaking there are other reasons/scenarios that could lead to not liking it or not being the favorite anymore or.....etc
Tbh I couldn’t care less to find out...Just enjoy what you like.
 

F_B

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Hehe just for the sake of it to show that Im not a binary iRacing hater/fanboy myself:
https://www.racedepartment.com/threads/iracing-is-overpriced.105970/page-7#post-3024891
:D

And still you come here and laugh about people who try to understand your problem with Iracing. Kind of provocative, isn't it? I have no problem with people disliking Iracing (and all other sims as well) as long as they have a comprehensable opinion but unfortunately most "opinions" are either a dislike or laugh reaction button, which makes a discussion less pleasant. But hey, it's internet in the 21st century and the toxic simracing community, so not really a surprise. :p
 

BrunoB

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And still you come here and laugh about people who try to understand your problem with Iracing. Kind of provocative, isn't it? I have no problem with people disliking Iracing (and all other sims as well) as long as they have a comprehensable opinion but unfortunately most "opinions" are either a dislike or laugh reaction button, which makes a discussion less pleasant. But hey, it's internet in the 21st century and the toxic simracing community, so not really a surprise. :p
Just like this post of you I think the best answer is the Haha button.
No reason to use too much energy :roflmao::roflmao::roflmao:
 
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thread alarm: can anyone bring us back on topic, for example how also after this update there are still problems with AI strength after saving the game in ACC. At first, I thought the problem was solved, but it's still there: upon starting a saved game, AI is about 4secs faster the first two laps at NürbGPand then goes back to normal - orcs in a state of battle frenzy.
It's all iRacings fault! ;)
 
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As I wrote earlier - in case you missed it - I'm not a fanboy because I enjoy all the other titles as well.
I doubt that, you pretend to like them and you lie to us (and maybe to yourself) in justifying that you are not a fanboy - your actions speak other words.
 
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I doubt that, you pretend to like them and you lie to us (and maybe to yourself) in justifying that you are not a fanboy - your actions speak other words.

:roflmao:

You're such a troll. You post off topic just to stir up :poop:. You don't actually add anything to the discussion. As soon as someone defends something about iR, you call them a fanboy. I can't take anyone serious who repeatedly counters somebody's arguments with 'oh, you're just a fanboy'.

And then you even have the audacity to tell someone what they don't like, claiming they are just lying to themselves. What on earth? Can you read his mind?

Either you're actually delusional, or you're just a troll. Hey, at least it makes me laugh sometimes. But it does get old pretty quickly.
 
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