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I'm a new user to Houdini and I'm trying to solve a problem involving piles of particles. I have a simple particle system that is spraying particles onto a grid, and I am using VOPs and point clouds to search for nearby particles and use the number of found particles to raise the Y position of the grid slightly, to simulate accumulation. The problem is in getting the particles to collide with this grid... the grid's shape depends on collided particles, but the POP network needs that same grid as a collision mesh.

After doing some reading here I feel like the problem could be solved using the Solver SOP, but I can't quite figure out how all the connections would work. I'm confused by the order of operations... the POP network collides with last frame's collision mesh, and then the collision mesh is updated and written to RAM, and then the next frame cooks? How exactly can I do this?

I'm attaching the scene in case anyone can help out. Thanks!


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This oughta work for you, there's a bit of vop raycasting in there to detect when particles pass through the mesh. I don't think you can use pop collisions for this, it's a recursion issue, so that's all moved to sops.

Thanks for helping!

So it seems that if my end result were to be particles (I'd be rendering a pile of salt or something similar), I would need to write out this collision geometry and then collide a duplicate of the original particle system against it, or what? Your system and mine are both making this geometry with slightly different methods, but I need this particle system or an identical one to start colliding against this geo. Should I be just emitting new particles based on what points are detected by the raycast each frame?

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