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nuki

Pumping Vellum Cloth

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I am testing a cloth sim on this simple mocap dummy and get this weird pumping throughout the sim. My initial suspicion was that it was caused by the framerate of the alembic cache I use as a collider, but that seems to be interpolated nicely when inspecting with float frame numbers.
The alembic cache is around 50mb so heres a OneDrive link to a cleaned up scene file. Theres really nothing beyond basic going on in this scene so I guess it would have to do with the cloth constraints. Since I'm new to vellum any suggestions on how I could get rid of that pumping (preferrably without filtering -> collisions) are really appreciated.

scene file

rr_test_v002.mp4

Edited by nuki

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i would

- remesh the dress to get a lower res geo just to help the sim moving along....say target size 0.015 ?

- add vellum attach to geo after the vellum Cloth, select a few prims near the side of the neck and the join at the back to attach them to the char.

- disable both friction wrangles, up the Solver>Forces a bit and see how you go.

- Solver>Foces>Vel Damping...say 0.1?

- Solver substeps start back at 1, constraint iterations 400

- also adjust cloth stretch stiffness if need be.

or why don't you just have a look at the modded file hey ?

 

 

vu_vellum_test.hiplc

Edited by Noobini

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3 hours ago, nuki said:

...My initial suspicion was that it was caused by the framerate of the alembic cache I use as a collider, but that seems to be interpolated nicely when inspecting with float frame numbers....

while it is interpolated, the actual animation is not smooth, which is causing your jitter

you can use Filter CHOP to smooth the motion of your avatar geo

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I suspected jitter in the walk animation, as well. I have never tried cleaning up an animation using CHOPs.

I can fetch the geometry and drop down a Filter, but how do I route that filtered result back into the SOP network so it becomes the new animation?

Untitled-1.jpg

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@Noobini thanks for the file - I will have a look in the evening! I did play around with attach to geo constraints, but deleted all of it in this simple example to exclude it as a possible source of error. I think you may be right about lowering the substeps since the pumping got worse with increasing temporal resolution . In the end I will probably need substeps tho because the whole thing should playback at 60fps.

@anim @Atom I still have to familiarize myself with chops, but it seems super useful for that kind of stuff. The Mocap data is baked from a retargeted HIK in Maya, so theoretically it would also be possible to do the filtering there.

Edited by nuki

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3 hours ago, Atom said:

I can fetch the geometry and drop down a Filter, but how do I route that filtered result back into the SOP network so it becomes the new animation?

use Channel SOP to bring it back

here is the file with CHOP filtering applied (green nodes), nothing else is different than the original scene (even though I locked the Vellum SOP)

 

2 hours ago, nuki said:

... The Mocap data is baked from a retargeted HIK in Maya, so theoretically it would also be possible to do the filtering there.

that would always be preferred

vellum_test_filtered.hiplc

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20 hours ago, anim said:

that would always be preferred

Because filtering does distort the mesh a little I presume?

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1 hour ago, nuki said:

Because filtering does distort the mesh a little I presume?

It does, which may or may not be ok

but ultimately because it is an extra step, if you can properly clean up your mocap data, do it

Then all departments consuming animation cache will have matching geo otherwise you'll have to export filtered mesh again for others to use just to align with your cloth. May be easier to manage for 1 person team, but still something to keep in mind

Edited by anim

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