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# Dirt 3 realistic driving mod

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4 replies to this topic

### #1levmans  Members

Posted 26 March 2013 - 02:15 PM

Hello. I'm recently trying to make realistic driving mod in Dirt 3(as much as it possible in ego engine). But i can't determine what formula codemasters used to write down highlighted parameters. can anyone help me with this? Car is Subaru impreza WRX.

length 4465cm, or 175.8''   width 1740cm, or 68.5,   height 1430cm, or 56.3'',    kerb weight 1520 kg 3351 lb

i've raised values a bit, because car originally was too "light", and I need to make it "heavier". but since i want it to be as realistic as possible, i want real formulated values.

Video of mod is here

p.s. sorry if i post in wrong place and thank you in advance for help!

Edited by levmans, 26 March 2013 - 02:18 PM.

### #2Promit  Senior Moderators

Posted 26 March 2013 - 02:25 PM

Inertia tensor is my first thought, but that should be a 3x3 matrix and if I understand correctly it's only three values for each variation of the car. Maybe it's modeled as a similar shape and the inertia tensor can be represented as a vector for a box or something along those lines.

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### #3levmans  Members

Posted 27 March 2013 - 12:04 AM

Inertia tensor is my first thought, but that should be a 3x3 matrix and if I understand correctly it's only three values for each variation of the car. Maybe it's modeled as a similar shape and the inertia tensor can be represented as a vector for a box or something along those lines.

http://en.wikipedia.org/wiki/List_of_moments_of_inertia  maybe "Solid cuboid of height h, width w, and depth d, and mass m" this is what i need?

### #4Hodgman  Moderators

Posted 27 March 2013 - 12:59 AM

In PhysX, it (or the setMassSpaceInertiaTensor function) assumes that your 3x3 Inertia tensor matrix looks like

x 0 0
0 y 0
0 0 z

So instead of accepting a full 3x3 matrix, it just accepts a float3, which is the diagonal x/y/z values above.

I don't think Dirt uses PhysX, but it's another possibility to investigate.

maybe "Solid cuboid of height h, width w, and depth d, and mass m" this is what i need?

Yes, that formula is valid if you're representing the car's mass distribution as a solid cuboid / rectangular prism, which is very common in physics engines.

The Iw/Ih/Id values in that math are the x/y/z values above -- the inertia value for each axis.

Edited by Hodgman, 27 March 2013 - 01:07 AM.

### #5levmans  Members

Posted 27 March 2013 - 02:40 AM

thank you guys for help. only thing is confusing-when i wrote dimensions in centimeters and weight in kg-result is too high values like (h 23 920 651), (w 22 897 005) and (d 5 283 854), if i divide it 10 000, tham maybe i get values that is "real". i can only guess what formula codemasters are using.

now it's clear how it works: there must be meters instead of centimeters now i have correct (i hope so) values (H 2392) (W 2289) (D 528). it's somehow works and car feels more realistic now. now i want to write down tyre wheel and engine inertias. i think there must be another formula for cylindrical object.

Edited by levmans, 27 March 2013 - 04:27 AM.

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