I was wondering if anybody could suggest a method on how to set the random seed when emitting from a nurbs surface. The only way I know how to seed particle emissions right now is to put a sort sop on the emitting geometry and emit from points. But this forces me to create a high density object which is what i'm trying to avoid.

thanks!

In Pops, did you try adding a Source POP, ref the NURBS surface, then select “Surfaces Random”?

Cheers,

J.C.

JColdrick
In Pops, did you try adding a Source POP, ref the NURBS surface, then select “Surfaces Random”?

Yes, that is how I setup my emitter in pops. You get a random emission, but what I would like to do is change the random seed and get a different random emission. Currently i get the same random emission every time. I was wondering if there was a simple way to seed the random particle generation.

thanks!
cesar

Interestingly, I was asking someone about that very issue in that even though random particle emission is selected, the pattern is merely looped.

Maybe you could try changing the birth probability?

You can birth via attributes…although I'm not sure how well that will translate over to NURBS. I'll take a look if I get a chance.

In the end, you don't really need to display the highres source surface - just display prior to birthing but source the convert SOP. I do it allatime…

EDIT

Yah, OK, it does indeed seem like the random birthing is unrelated to uv or anything else - it must do some internal evaluation of the surface, then mojo's that up to do random birthing. Since it's mojo, you can't seem to get at whatever is determining “random”. Bummer.

It seems that the only way to work around it is the way you've been doing it - doing a randomization somewhere where you *can* get at it, like SOPs, and then feeding that into your Pops. Of course, you can't really avoid converting to points, or fiddling with attributes. Don't forget, though, it's not really inherently any slower(which you inferred I believe in the first post) - if you want points spawning from many different locations, those locations need to get evaluated no matter what - spline or poly. You can also try tricks like Ed suggested - variance, breaking up birth probability - although as you likely know this isn't quite the same. Might get you the results you want, however.

This would be a good RFE - access to the seed for “random” birthing in the Source Pop…

Cheers,

J.C.

Thanks for the help! I guess for now I'll just stick with converting to polys until a seed option become available. The overhead of converting to polys isn't bad at all. I guess I was hoping that there was a random seed entry somewhere I was missing


have a great day!
cesar

talos72
Interestingly, I was asking someone about that very issue in that even though random particle emission is selected, the pattern is merely looped.

That is quite true. Generally the (random) birthing methods cycle through all of the entities, but in a randomized order. Try the (attribute) methods for more probabilistic birthing.

That being said, unfortunately, there is currently no way to specify the random seed.

Would altering the UV of the geometry being used for birthing particles change the randomized order?

I tried that and it seemed to be unrelated to the mechanism used for birthing.

Cheers,

J.C.

Don't know if it will help you…
On the Sort Sop, enter $F(or any $F expression that suits you) in the seed field.
Cheers,
Silvina