How individual car being modeled?

[Sampaynehahah]

I’m a new GT player and used to play a lot of assetto corsa and forza. I’m wondering how each individual car being modeled in this game.
On one hand, you have assetto corsa where each car is modeled individually, scanned, so handling is different even for similar powered car. On the other end of spectrum you have forza, each car is just a box and handling is coming from a spreadsheet with same parameters just different values for each car.

I’m wondering where gt fill in the spectrum. I only played a few days but it seems each car is somewhat different but not too different. Anyone here has more insights?

 

[eran0004]

I don’t understand. If you change the parameters of the physics model you do change the handling. And I don’t know how you would scan the physics properties of a car? Are you thinking about the 3D model perhaps?

 

[Sampaynehahah]

I don’t understand. If you change the parameters of the physics model you do change the handling. And I don’t know how you would scan the physics properties of a car? Are you thinking about the 3D model perhaps?

Yeah. I think that's a fair point. I think the car being individually modeled means their physics engine is complex enough to support modeling the car in more details, idk, like could model different type of suspensions, for example. This gives unique handling for individual car within same class. same for iRacing.
Where as forza, each class of cars share one type of box. and their physics engine is much simpler compared to ac, so it's very hard for them to model cars within the same class to give you unique driving experience.
I feel like GT is something in the middle.

Car Technology - iRacing.com

Realistic vehicle dynamics begin with accurate data. That is why iRacing.com works directly with auto manufacturers and race car constructors.

www.iracing.com

 

[Samcastor]

I’m a new GT player and used to play a lot of assetto corsa and forza. I’m wondering how each individual car being modeled in this game.
On one hand, you have assetto corsa where each car is modeled individually, scanned, so handling is different even for similar powered car. On the other end of spectrum you have forza, each car is just a box and handling is coming from a spreadsheet with same parameters just different values for each car.

I’m wondering where gt fill in the spectrum. I only played a few days but it seems each car is somewhat different but not too different. Anyone here has more insights?

As someone else pointed out, 3D scanning is used to model the geometry of the car. Now, it is possible to use that model for CFD but beyond that all other parameters that would make a car unique to drive are not derived directly from this model. So for the most part, the feel of cars and the scanning process are independent of each other. I guess the Aero modelling can make a good bit of difference but certainly that is not the only difference between cars in GT and similar games. In fact, the spreadsheet parameters you mention are probably the more pertinent characteristics making cars feel different.

Yeah. I think that's a fair point. I think the car being individually modeled means their physics engine is complex enough to support modeling the car in more details, idk, like could model different type of suspensions, for example. This gives unique handling for individual car within same class. same for iRacing.
Where as forza, each class of cars share one type of box. and their physics engine is much simpler compared to ac, so it's very hard for them to model cars within the same class to give you unique driving experience.
I feel like GT is something in the middle.

Car Technology - iRacing.com

Realistic vehicle dynamics begin with accurate data. That is why iRacing.com works directly with auto manufacturers and race car constructors.

www.iracing.com

So having looked at this video and I like to think think I am over the peak of the Dunning Kruger curve, an obviously reductionist way of looking at this is that IRacing is indeed doing exactly what you are accusing Forza of doing. They have models for these components and effects in parametric form and the you can "populate the simulation" as they put it with data from the manufacturer or other sources the devs have access to like scanning. For example, you see the Aero modelling is reliant on some key factors like drag/lift coefficients, etc. and they can use these in a quite literally a spreadsheet for some examples in the video to model the behavior you need. Mind you, this approach is a very very good approximation if done well in this context and really the validity of CFD as a whole is another can of worms entirely.

That is not to say that these things cannot be done in another manner. I think a great example here is when they talk about the suspension. Now, you the suspension of cars in the general form is well known and you can easily find equations to model the behavior and with a Bachelor's degree and some google you can derive these equations yourself. In this particular example they show the suspension geometry with the unique component they describe as banana-shaped that is clipping the tires. Now, you would need to alter the equations you have derived for your regular geometry system using the MSD model but if you pay close attention they say they model the kinematics and not the kinetics. Small difference in colloquial terms, but not in technical ones. What it means essentially is that it is possible they simulate only the motion of these components to animate them faithfully as they do show later on but do not bother with the kinetics (or the forces that act upon it to derive the motion) for this small difference in suspension. Now, I am not accusing them of anything and it is possible they do both but their choice of words and that presentation certainly gave me that idea. Taking a look at these papers might help you see the differences in modelling (https://www.koreascience.or.kr/article/JAKO200311921771419.page)
(https://link.springer.com/article/10.1007/BF01274249?noAccess=true) - Paywalled sadly

 

[GBalao888]

I think this is mainly the process for getting a car to be built for the game:

Licensing - Sourcing - Photography/Scanning - Sound Recording - Modeling - Rendering - Implementation - Quality Control - Release

"Implementation" means adding it into a special build of the game, already with its physics based on the realistic specifications.

All of that would take roughly three to six months to build a single car from scratch just for the game (three months if the car in question is outsourced).

As far as what I've heard, some cars just need the CAD (Computer-assisted drawings), while some really need a physical car to work on from there.