hi,
i use vopsop to control the color impact in ground.
i just need the color take 2 frames after ground contact and return to black.
how can do this in vopsop.
thanks

Since you're not using pops or dops to generate your motion you don't get impact data for free and your scene doesn't know what came the frame before it. So, your collision, isn't technically a collision. What I whipped up for you is as close as I could get without completely rebuilding your setup.

If you end up simulating the motion in pops you can get all sorts of useful information using the collision POP.

http://www.sidefx.com/docs/houdini12.1/nodes/pop/collision [sidefx.com]

I assume you can get the same in DOPs, but I'm not as familiar with them. Here's a thread on that:

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=96409&sid=c3ca53406ad7b5ce7e2496945b1d29b5 [sidefx.com]

thank you kleer.