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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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F_B

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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.

Dude, please check a psychiatrist, it's getting out of control. :laugh:
Do I really need to post pictures of the times I spend in the different sims? Discussing with you and the other trolls is just a waste of time as you're unable to really understand each others arguments. So, bye bye and welcome to my ignore list. :inlove:
 
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I really wonder when they are gonna show the first teaser for rain. They teased the damage model long before release too.

I think this article really shows how rain can help with other aspects of the sim. People always complain that they don't want/need dirt or rain and how it's a waste of resources. But all of these big projects come with side effects that improve the experience for everyone - like this, it'll help oval drivers even though they don't drive in the rain. Or the off track and marble behavior that basically was influenced by dirt development.

I'm curious to see how well rain will work with the laser scanned tracks. One thing I always liked about iR tracks was how well they captured small little details in the surface that transfer well to driving the real track. It's great for preparation.

With rain, if they get the drainage accurate, we should see puddles form in the same spots as they do in real life. Its another little detail to learn about each track. Will we have running water? Some tracks literally form little streams running across the track. So many questions, but it'll be interesting. Simracing still has a hard time capturing driving in the rain very well.

Proper hydroplaning seems to be an important aspect of it, Kunos already had that in netKar Pro, and it was the first time driving in the rain made me think 'wow, this actually feels pretty good'. And while rF2s weather system is nice, and I love the handling, rain always was meh. Especially full wet tracks. Or how well the wrong tires used to work. But they don't have proper hydroplaning (unless they added it since I last chose a rainy session and I missed the news), so that might be why.

Do I really need to post pictures of the times I spend in the different sims?

Nah, its blatantly obvious you spent all that time driving those sims so you can generate proof that you're not a fanboy. You actually hated the time you wasted with them.

...:D
 

BrunoB

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With rain, if they get the drainage accurate, we should see puddles form in the same spots as they do in real life. Its another little detail to learn about each track. Will we have running water? Some tracks literally form little streams running across the track. So many questions, but it'll be interesting. Simracing still has a hard time capturing driving in the rain very well.
You will probably get disappointed if you think that the rain and puddles "will locate itself" the same places as it does in RL on the different tracks.
The reason is that there is a huge difference between the laserscanned tracks graphical surface and the hidden virtual "net" every car drives upon.
Because the resolution (mesh size) of this net is way lower than the graphical track surface displayed.
So if the virtual water dont get some stuctured (and "artificial") help it cannot position itself where it is supposed to.

ByTheWay: All this under the precondition that iRacing can/will provide rain inside a reasonable timespan.:sneaky:
 
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Discussing with you and the other trolls is just a waste of time as you're unable to really understand each others arguments.
Seems like you have the problem a lot - you must be the problem then, not us.
But I am not surprised after you already lie to yourself about your biases.
 
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You will probably get disappointed if you think that the rain and puddles "will locate itself" the same places as it does in RL on the different tracks.
The reason is that there is a huge difference between the laserscanned tracks graphical surface and the hidden virtual "net" every car drives upon.
Because the resolution (mesh size) of this net is way lower than the graphical track surface displayed.
So if the virtual water dont get some stuctured (and "artificial") help it cannot position itself where it is supposed to.

I know how the visible and physics - layers work, but I don't know how that stops the collection of water in realistic spots.

I'd assume, that the collection of water is based on the physical layer, not the visual one. On the visual one we'll just see some effect of wetness based on what the graphics engine gets from the physics layer.

I highly doubt the collection of water would be based on dips and bumps in the visual layer. So while the graphical representation might not be 100% accurate, puddles would still form based on the laser scanned track surface and at least roughly represent that graphically.

Its kinda like with dirt. Dirt track surfaces are physically a lot less smooth than the actual polygon surface we see. But at the same time, thanks to some graphical effects, the polygon surfaces also look a lot less smooth than they technically are. I think we'll see the later with wet tracks too.

A lot of stuff in iRacing looks a lot more 3 dimensional than the model actually is. They've improved a lot on those effects since I joined too, I know that tire walls for example got a pretty nice looking update at some point.
 

BrunoB

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I highly doubt the collection of water would be based on dips and bumps in the visual layer. So while the graphical representation might not be 100% accurate, puddles would still form based on the laser scanned track surface and at least roughly represent that graphically.
My point is that both you and maybe even I would probably be rather dissapointed if we was actually told how much difference there exist between the nice track surface which is displayed and the actual coarse net "tarmac" the cars (and future water) meet.
So if you "highly doubt" the water is positioned based on the visual layer - then we are only discussing what "roughly" means in your "roughly represent that graphically".
A lot of stuff in iRacing looks a lot more 3 dimensional than the model actually is. They've improved a lot on those effects since I joined too, I know that tire walls for example got a pretty nice looking update at some point.
I fully agree with that. Because all the way back to iRacings forerunner the NR2003 I have allways felt there is something rather "realistic" 3D feeling driving on NR2003/iRacings tracks compared to most/all other racing games.
Hehe eventhough both ACC and pCars2 graphically looks much more "sofisticated" (IMO).:)
Hehe Raceroom my favorite at the moment comes somewhat close to the same "realistic" 3D feeling but does not fully live up to the strange NR2003/iRacing feeling of actually "being there".:thumbsup:

EDIT:
Sorry! Because maybe "feeling" wasnt exactly the right word to use in my above: there is something rather "realistic" 3D feeling
Because the "realistic" 3D feeling is purely visual.
Absolutely not conserning iRacings car behaviour :poop:
 
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OnTopic: and then there are white concrete and black rubber "race trajectory" part of road... should be massive difference in heat absorbed AND grip/behavior under the rain (sorry, could not resist)
 
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It all seems like far too much effort going into something that could just as easily be fudged.
A real race driver (I'm talking about us armchair experts here) will look at an area of shadow and know that the cool surface is going to give 5% more grip. Hurtling out of the shadows, we quickly enter the sun-facing 7 degree banking and know that we are going to slide a quarter car-width up the track more than we would on the identical turn 3-4 that is in the shadows.
The shadows of trees on the track are going to reduce our braking distances going into the corner by 5 metres.

So if we know this stuff already, why bother with calculations?
I would rather have 1/2 Lb of Fudge than 1Kg of incredibly complex code that could easily be hiding some rare killer bacteria.

I hope (because I do like iRacing) that this might lead to oil-spill calculations and that sand/dust on the track at Laguna Seca actually affecting how I drive (Because I damn sure can't tell if it has ANY effect.)

When others claim they can feel these subtle boundaries and actually change their inputs accordingly, I always suspect placebo effect - but I am a terrible driver without DD; I may be the colour blind man trying to appreciate a rainbow.

Fancius Latinus Phrasius : I am mostly a road racer, and perhaps all this stuff is much more noticeable and important on an oval.

TL:CBA2R I doubt it will affect how I drive.
 
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