Hello everyone,

I'm currently working on a shot in Houdini where rocks are meant to shake and rumble their way out of the ground. In my RBD simulation setup, I've modeled the ground plane with some mountain noise to give it an uneven surface. Some of the rocks are initially clipping through the ground plane, as they need to emerge from their resting position inside the ground. However, due to the clipping at frame one, the Bullet solver is allowing these rocks to continue falling through the ground plane.

I've already managed to achieve the shaking effect, but the issue of the rocks falling through the ground is preventing me from completing the shot.

Can anyone provide some guidance on how to prevent the rocks from falling through the ground plane any further, despite the initial clipping, while maintaining the rumbling effect?

Thank you in advance for your help!

Best regards,
Vincent Griffith

Translate them above the ground plane and use a few pre-roll frames to allows them to settle naturally.

Yeah I ended up doing that, just was really wanting them rising out of the ground so half of each rock would be obscured. What I ended up doing was post sim animated it translating up once the rocks started shaking and that seemed to be fine.

There's a number of ways to do this.

You could animate the packed RBDs rising before the sim, set them to animated=1 and active=0, and switch to active=1 and animated=0 once they're out of the ground (i.e: use the Winding Number SOP to figure out if a rock is inside the ground or not).

You could turn the ground collision geometry to a heighfield and push it down where the rocks are using a heightfield project, animate it returning to the shape you want over a few frames by animating upwards the rocks you are using to heightfield project, leave all the RBDs as active, they should slowly be pushed upwards.