Hey all,

I`ve been playing around with RBD and have a slight issue. I have a scene with a lot of spheres on a displaced grid which are attracted by a point. Everything works fine except that some of the spheres are intersecting the ground geo (the displaced grid) and others seem to be floating above, but only a tiny bit. I set the collision shape in the collision tab of the RBDBULLETSOLVER to concave. But where can I increase the precision setting so this won`t happen?
Thanks in advance!

S.

No answers or hints for a week...maybe what I described wasn`t clear enough? Should I upload the scene?

Otherwise this is very likely one reason Houdini is still seen as a complicated software and so far it`s also the reason why I`m hesitant going into more complex setups because I fear to end up in a dead end and nobody can suggest a solution...and it`s rarely possible to share scenes...

How do you solo artists like me approach cases without any helpful solution from forums?

It's common to share scenes, you don't have to share production scene, just a simple one showing your issue

Concave colliders in bullet can be hit or miss, if you can it's better to avoid them

you can likely convert your displaced grid to heightfield and then bring to dops using Terrain Object DOP in heightfield mode
Or if using Bullet Solver SOP set Ground Type to Heightfield
Collisions with heightfields are efficient and should be precise

Thanks Tomas, I`ll try that!

I never used heightfields so I had no luck in converting them. But I attached a scene file - if anyone wants to take a look I`d be grateful to learn how to fix that...

Here's an updated hip file that should fix any floating issue you have.

Generally, if your collisions are off, the first thing you want to do is look at the collision geometry itself used by bullet. The RBD Bullet Solver SOP has a few options in the visualization section to help with that.

With spheres, you'll have a much faster sim if you use primitive spheres or the Sphere bullet geometry representation.

Another thing that might impact your collisions is the collision padding. If your colllision shapes end up disappearing or not being precise enough, reducing this can help.

I've included an example of using your ground geo as heightfield, however, internally heightfields are converted to concave colliders so you won't see much improvement there - this is something we're looking to improve.

here is an example of heightfield ground collider, I kept only the SOP version and also switched spheres to Primitive to make the whole sim faster if you are ok with perfect sphere collisions

npetit
Here's an updated hip file that should fix any floating issue you have.

Generally, if your collisions are off, the first thing you want to do is look at the collision geometry itself used by bullet. The RBD Bullet Solver SOP has a few options in the visualization section to help with that.

With spheres, you'll have a much faster sim if you use primitive spheres or the Sphere bullet geometry representation.

Another thing that might impact your collisions is the collision padding. If your colllision shapes end up disappearing or not being precise enough, reducing this can help.

I've included an example of using your ground geo as heightfield, however, internally heightfields are converted to concave colliders so you won't see much improvement there - this is something we're looking to improve.

Thanks for the file and your suggestions/hints!

tamte
here is an example of heightfield ground collider, I kept only the SOP version and also switched spheres to Primitive to make the whole sim faster if you are ok with perfect sphere collisions

Thanks again, Tomas! It`s very appreciated!

Signum
I never used heightfields so I had no luck in converting them. But I attached a scene file - if anyone wants to take a look I`d be grateful to learn how to fix that...

I just started, what should I do first, any chance you can help me?