Hello:

I have a question about the collision of grains in Houdini. I am messing around with the Sand Box shelf tool, trying to get some snow-like foot print deformations. I found this video, here:

https://vimeo.com/147220152 [vimeo.com]

In that video, the foot makes a deformation in snow surrounding the foot. All the surrounding snow is at rest. My problem is that when the foot dips into the sand box, the collision affects every particle in the box, rather than just the particles near the foot. It looks more like putting an ice cube in a glass of water, and the ice cube displaces water. When the foot hits the grain, it affects all the particles all the way to edge of the container, sometimes pushing them out of the sandbox. Not sure if I explained that well, I can upload an example if I did not. What should my approach be to getting more realistic (in terms of how snow foot prints look) deformation in the grain particles? The snow needs to compact where the foot steps, not overflow the container.

If you start the particles inactive, and only activate them when they get close to the character's feet, you should be able to keep everything else still. It'll also help your sim times.