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How to Setting "Scene Units In Meters".

Message 1 of 7
1058 Views, 6 Replies

How to Setting "Scene Units In Meters".

when i cloth sim with bifrost mpm solver,

i don`t know what is corrective value of 'scene units in meters'


My maya working Units of Preferences is Linear : centimeter

and i made character size is 1/10 of real world size.

ex ) real world 180cm man : maya 18grid

so 1 grid is 10cm.


then i made bifrost graph for cloth.

and change values.


# mpm_solver_settings

Scene Units In Meters : 0.1 ( because my 1grid is 10cm)

Detail Size : 0.015 (because collision)


My Question is...

1. Is it correctly value of scene units in meter , detail size ?

2. gravity is y -9.8 is correct?? or -0.98 ?? (because i think ...change all value 1/10!!)

3. should i change properties of make_mpm_cloth node?? like Mass Density, Viscosity, Vibration Speed, Collision Max Speed....


I confused ...

should i change all value 1/10 or not. 🙂



Message 2 of 7
in reply to: jbg0115

Have you seen this video?

Message 3 of 7
in reply to: jbg0115


I recommend to keep it simple.

1 unit = 1 meter (for simulation and dynamics, just ignore the "cm" label), then you can keep all unit related simulation settings at default values.

So you need to make your character 10 times smaller and you are done.

Message 4 of 7
in reply to: mspeer

if change Scene Units In Meters..

I have to change variety attributes.



Can you know the rules how to change it?

like...Mass Density, Viscosity, Vibration Speed, Collision Max Speed...etc..


mass denity is kilograms per cubic meter...

viscosity is meters squared per second.

vibration speed is meters/second.


so i confused  how to change it. 

Message 5 of 7
in reply to: jbg0115


If you created your scene content in a scene with units set to meters, then everything is larger by a factor of 100 ("cm" to "meter"), so you need to adapt all related values also by a factor of 100 (for squared values it would be 10000).

Again, I don't recommend this.

Message 6 of 7
in reply to: jbg0115

FYI, Inside Bifrost Graph, what scene_scale_in_meters does it scale the geometry up or down inside the solver, simulate, and re-scale the geometry back to the original size. 

For exemple, if you're using maya unit as centimeters (the settings doesn't matter), you have a character that is let's say 180cm so that's units high, and you want to simulate a piece of cloth, then you can set scene_scale_in_meters to 0.01, and then the input meshes will get simulated just as if your model was modeled using units as meters (1.8 units high). Finally, Before exiting the solver, the geometry get scaled back to 180 units high.

So in the end, it's not necessary to pre-scale the geometry, you just gotta set this value property before tweaking your simulation settings. Just understand that 1 maya unit = 1 meters inside the simulation solver, and use the proper scene_scale_in_meters value so that it matches the pseudo unit system your model is using.

Personally When doing cfs, the character I use are all using maya unit as cm, so i'm always settings the scene_scale_in_meters to 0.01.

Maxime Jeanmougin - Technical Artist

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Message 7 of 7
in reply to: mjcg91




Other dynamic systems in Maya also have global scale attributes, so if there is one global value and you use it, there is ("should be") no need to change other scale related settings individually.

In the end only the result matters, if it looks good no one asks what settings you have used.

(I have seen simulations where some values have been off by a factor of 10 and it still worked for that particular cases.)

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