I saw Jeff Lait's video “Houdini 9.5 Fluids Overview” on Fluids Technical Evening and i'm recreating a similar wave situation. But I don't understand how to isolate particles that collide on the rock (in the video it says: “isolate the particles which will be used for the hero splash, in this case,based on $VY>=5 and a white color passed from the rock”) to build the hero splash. Can you help me, please? Do you have some example?
Thank you very much in advance!
Bye,
Mirco

The Attribute Transfer SOP was used to transfer the rock's attributes to the particle field.

See the attached example file.

Tip: You can use the expression
@Cd.x>0.1
in the group field of a Blast SOP (any SOP that takes varying local attributes). Blast is a bit more efficient than Delete with expression. There is both a Blast and a Delete SOP so you can see two ways to cull the points of interest.

Thank you very much Jeff!