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TOPIC: Intersecting Carbon morph failure

Intersecting Carbon morph failure 6 months 3 weeks ago #102

  • dantom
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Hi all,

I've been doing some testing with Carbon Morph in Houdini 17 for a method of de-intersecting animating geometry. I've come across scenarios where the intersection is so great, that the mesh gets stuck in an inside-out configuration. It's similar to issues in Cloth where once a cloth goes inside a collider, it will never come out again.

Do you have any suggestions on how to get around this issue?

I've attached an example file to show what I'm talking about.

Thanks,
Dan
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Intersecting Carbon morph failure 6 months 3 weeks ago #105

  • Sebastian
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Hi Dan,

With problems like this, there are usually 2 reasons for why this is happening:

  • Too strong goal skin strength
  • Too large Inner Fatness

First of all, I like to think that Collision is the king of every simulation, meaning it is usually the strongest constraint and everything else has to bow down to it. And if anything decides to fight collision too much, bad things happen.
What you see in your scene is because collision wins.

Your goal skin strength is set to a very high (1000 painted range) value.
This really tries to force the skin to follow the goal. But since the goal is pushing the hand inside the body, you have the goal constraints fighting collision, and collision wins, which causes the hand to not be able to penetrate the body. The palm of the hand gets stopped first and then the back of the hand gets pushed to the same position, which causes the 2 sides of the hand to come closer and closer to each other, i.e. hand flattens. And once the back of the hand is within a distance of Inner Fatness of the palm of the hand, it gets sucked in by the Inner Fatness, which pushes the palm straight through the inside to the outside of the back of the hand, and vice versa. Hence the inside-out configuration. The simulation will almost never recover from this.
This effect is also explained in our User Guide->Fatness

Therefore, the first thing one could do is to set the Inner Fatness to 0 to prevent the geometry from sucking each other in.
The result looks much better, if you give it a go.
You will see some temporary inversions, but the simulation actually recovers from it.

But, I would not recommend this as a general solution, because Inner Fatness exists for a reason and should be used when possible. You can find more information about this in our User Guide->Fatness.

What I would actually recommend to solve your problem is to lower the goal skin strength.
I would like to point you to the tutorial right before the one where you got the example hip file from: Tutorials->Morph->Avatar Morph
It explains how to best set up the values for the goal skin parameters.
Here is an excerpt:

Now, set the Base value. A good value is large enough to keep the avatar body from falling under gravity, but not much larger. Too small of a value will later allow the body to easily deform, while too large of a value preserves the shape too much and still corrupts the cloth. In this example, 10 is a good value.

In your scene, you do not have gravity turned on, so I would temporarily turn on gravity. If I set the goal skin strength value to 20, the character stays in place and doesn't fall under gravity.
This is the minimum requirement. Obviously, if you want to increase that value to make it more stable.
Especially when you put clothing on the character, it needs a stronger value.
But nonetheless, your value was set to 50 times the minimum value required.

If I run the scene with 100 goal skin strength, you will get a corruption free result.

At last, you might want to set parts of the morph kinematic if they are not supposed to deform, or at least paint some areas stronger than others. This can be used to limit the deformation of the hand and instead push the belly more, rather than flattening the hand.
Please refer to Tutorials->Morph->Skin Deformer Morph for more information on this.

I hope this helps.

Cheers,
Sebastian

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Intersecting Carbon morph failure 6 months 2 weeks ago #114

  • dantom
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Hi Sebastian,

Thanks for the detailed write up.
I'll experiment with some of the settings you mentioned, and see if I can get some better results.

Thanks,
Dan

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