I'm trying to detect collisions for a pop sim using “pop grains” in H14. I've attached a sample file.

The problem I'm having is…

When I'm simulating regular particles, the collision detection works fine. The particles change colors when it enters my collision object (as expected).

When I'm using the pop grain simulation, the collision from the ground is also changing the color of the particles?

Is there a way round this?

Hi its not unexpected behaviour to have the collisions with the grnd plane considered as its classed as a RBD static object.
Though it is odd how particles hit > change colour when the geometry has not been selected in the collison POP . That could be a bug inquiry for the pop collision node ( colour attribute ) .

To get round the visual issue, why not just use the hit count attribute and make a group based off that , which you can colour. After all the behaviour is correct , just the colour attribute part of the collision seems incorrect.

Hi,

I'm actually fairly new to Houdini and I'm not exactly sure how to pull all the variables from the particles.

I've tried using a pop wrangle with this vex code:


if (@hitnum >= 1){
@Cd = {0,1,0};
}


It produces the same result as what the popcollisiondetect node does

I did find another particle attribute called "hitpath "
I tried multiple ways to create a group using $HITPATH or in a vex code @hitpath but I haven't had much luck.

If you can provide a sample scene file that makes this work, that would help.

Thanks!

It seems like I misunderstood the “accumulate” checkbox in the popcollisiondetect node. I disabled it and the collision detection is now doing what I was expecting it to do.