Cloth Collision Issues

[Juzwa]

Hi, 

So I've done some simple cloth sims before and from what I remember the collision with object is pretty straight foreward.

Now Im trying to do some more complicated sim (cloth attacked to a body). I dont know why the constraints (for surface attachment) and collisions are not working when I use deforming geometry.

Here is a simple example (its 50mb, sorry, but character alembic cache...)

https://dl.dropboxusercontent.com/u/22676624/CollisionIssue.zip

Edited October 26, 2016 by Juzwa

[Atom]

There are quite a few issues in that file.

1.) You need to bump up the collision guide on the Static Object quite a bit, the default of 30 does not even make solid geometry to collide with, try 128 or higher.

2.) The normals on the person are all messed up try adding a Facet with Post-Compute normals turned on. Also the UVs are in bad shape.

3.) Cloth needs some start-up time before you start leaping around. I usually put at least 24 frames of basically static geometry up front to give cloth time to settle down before I begin movement. You can always remove this startup time later once you have a bgeo sequence for your final. You can emulate this by simply turning off Deforming geometry on the Static Object. Try to get the shirt to settle down and act normal on a static pose first.

4.) Don't ignore warnings on your nodes. Middle click to see what the problem is. Those constraint points seem to be invalid. Delete that node and try recreating your points.

5.) With high velocity motion on your collision object you will probably need to spend more time sub-stepping to get the cloth to track.

If you can, try some simple slower animation like a person standing and swaying back and forth, or a walk in place as you first animation.

Edited October 26, 2016 by Atom

[Juzwa]

Thanks Atom, I tired all above and none has halped.

So Im doing now the simple scene. Animated sphere and a grid. And still for some reason animated geometry does really bad collision. The cloth object tends to fall through and my constraint has errors pointing to collision obejct (attach points were not valid for the current goal).

I created the constraint with shelf,  tried manually, tried different groups, tried different goal objects.... im fighting with this half a day already and still no idea what actually causes the error.

Big thanks to anyone that knows what might be wrong (but please just dont reply "try vdb in collision")!

Simple scene:

 

CollisionIssue.hiplc

Edited October 28, 2016 by Juzwa

[Juzwa]

Ok, I finally got to the issue.

So finally I tried to check the primitive numbers in the viewport, to my surprise my goal mesh was not actually a polygon mesh, so It had no primitives except one, the object itself.

This was a painful lesson to learn that a mesh in Houdini is different than a poligon mesh. Because it literally took me the whole day to figure it out... Just simple convert sop fixed everything. I will remember this lesson till the end of my days!

[Cockochan]

On 28/10/2016 at 7:39 PM, Juzwa said:

Ok, I finally got to the issue.

So finally I tried to check the primitive numbers in the viewport, to my surprise my goal mesh was not actually a polygon mesh, so It had no primitives except one, the object itself.

This was a painful lesson to learn that a mesh in Houdini is different than a poligon mesh. Because it literally took me the whole day to figure it out... Just simple convert sop fixed everything. I will remember this lesson till the end of my days!

Just want you to know you answered helped me and i hope a lot more people to not spend a day on solving it

[anbt]

@Juzwa Hello, I am quite late to the party but I have I think a similar issue. 

I drapped some kind of dress around a Mixamo model. It works fine but then, when I start my sim and my model starts walking, the dress doesn't collide at all. I realised it was because I edited the model and the topology is changing every frame. I mean the points of the model are changing each frame. The mesh isn't really static. I guess it happened because I inflated some body parts with VDBs and now the arms are merging with the hips as the model is walking, but I want to keep that effect.

So I thought that was the cause of my collisions problems. I tried with a normal Mixamo sequence and I didn't have any issues. So It definitely is because of the changing topology of my model.

It seems that the solution would be to convert my walking model into a collision VDB object (correct me if I am wrong) and do this in DOPS, import the drape as vellum source. But it still doesn't work
My static object in DOPS (my walking model) is set to:

- use deforming geometry
- create active object (tried both on and off)
- collisions detection set to volume (I also tried surface)
- Volume sample mode

It is not working. The cloth is kind of colliding, but intersect with my model and it is really jittery.
I have increased substeps with no change.

Any clues?? 

Thanks a lot