[Sidefx-houdini-list] POP's: best way to threshold particle emission based on an point attribute

François Duchesneau sidefx at trinix.ca
Mon Nov 15 20:28:58 EST 2010

Me too I prefer to create my emitter in sop. The advantage is that you 
can see your emitter points and normals (which are then used for initial 
velocity in pop) as Rangi stated. Also, when you apply noise on  scatter 
points, it is a lot more precise than a noise on a surface from which 
the emission on surface will interpolate from.

The disadvantage is the speed so I almost always bake raw points with 
the number of substep I plan to use. I do that locally and even if it 
takes me 3 minutes to bake, after that I usually don't need to do it 
again since most of my changes are on the emission noise on density, 
normal length and orientation and this doesn't have to be baked to be 
fast since I do that in vop.


Miles Green wrote:
> Hi,
>  does anyone have any recommendation's for the best/fastest/most 
> efficient way to birth particles from polygons based on a custom point 
> attribute?
> the two methods I currently have are;
> 1)  inherit the custom attribute into pops via the source node, then 
> follow it with a  kill Node that checks if the custom attribute is under 
> a certain threshold
>   - NOTE: this seems wasteful to me as the particles are created and 
> then killed
> 2) use a scatter  in sops before the popnetwork to create birth points 
> on the poly, and then use a delete Node to delete those points where the 
> custom attribute is under a certain threshold
>  - NOTE: this seems slower than solution (1)  above
> I ideally would like to use the custom attribute directly in the popnets 
> source node to specify that particles never get created if the custom 
> attribute is below a certain value
> thanks for any help
>   Miles
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