The POP Collision Ignore node can be used with Vellum in DOPs, which lets you specify which objects to ignore collisions with using the collisionignore attribute. The following illustrates a simple example where the green cloth ignores the torus and the blue cloth ignores the box. You can see that the blue cloth falls through the box, but is resting on top of the torus. The green cloth is falling through the torus, but is resting on top of the blue cloth and the box.

There currently isn’t a SOP equivalent to the POP Collision Ignore node. However, you can use an Attribute Wrangle to set up these rules.

Handling collisions in Vellum can be tricky, since there are often multiple objects inside one Vellum object. In order to deal with this set up, there is also a collisiongroup attribute which allows you to set collision rules independently for pieces inside the object. For example, you can put the thumb of a character in a separate object even though it’s part of the body.

This is very useful for cleaning up interactions between cloth and characters in simulations. For example, you may want the thumb to interact with the sleeve, but not interact with the pocket because it gets caught. You can do this by setting up rules in an Attribute Wrangle node to allow collisions between the thumb and sleeve and disable collisions between the thumb and pocket. Often the parts you want to ignore are subsets of larger pieces of cloth, so you can make the thumb ignore collisions with the pocket, but still interact with the rest of the pants. Additionally, both the collisiongroup and collisionignore attributes can be animated with a static collision, or turned on and off in DOPs with a rule.

See the Vellum Attributes page for more details on writing rules using these attributes.