Hi Brains trust

POP Source > Emission Attribute > From the help

When in surface mode, this point attribute will be used to vary the chance of any polygon from emitting polygons. Higher values will increase the relative chance of that polygon getting an emission.

From this I was thinking if the Cd attribute is of a zero value ie black , there should be no emission of particles. Of course I have tested and set my Cd value to black , but I still get the emission of particles, so this got me wondering how is the probability calculated when an attribute is selected. As I often use color to drive where I want more emission.

Rob

by default the number of points is computed from birth parameters (impulse and constant rate)
and the Emission Attribute is like a distribution of those points, so no matter what values your attribute contains the point number will be constant, just differently distributed based on the attribute value distribution
(so in case of uniform value of 0 evenly, as for any uniformly constant value)
(if you can ensure, that your attribute is not constant over the whole source, you will get 0 particles in parts where value is 0)

to get the effect you want even for uniformly constant values, check Scale Point Count By Area checkbox
in that mode (besides that it computes pointcount by scaling birth parameters by area) Emission Attribute directly scales density too, so 0 will always result in 0 particles, etc.

Hey guys! I found this thread after I ran into a similar problem as circusmonkey. I followed tamte's advice as best I could but the particle emission is still uniform across the geometry. I'd ideally want denser emission from the red spots while still having some slight emission from the non painted part of the geometry.

I've attached my hip file and an image of the general look I'm going for. Any feedback would be really helpful!


Bonus question- would it be hard to convert the POPs to smoke for a similar look?

Hi, I have made you an example, using a attribute wrangle sop on how to control density using @Cd.r

Rob

I know this is an older thread, but if anyone knows, saving me from doing some setups to determine what I wish to know…

from tamtes' post:

… just differently distributed based on the attribute value distribution…

Does this mean that my range of values I set for the attribute that I will use as the emission attribute will get “automatically” fit to their min/max values.

Meaning whatever the min/max value range I create with my attribute, I can expect a relative probability mapped to that range?

Docs are saying:

“…Higher values will increase the relative chance of that polygon getting an emission…”


e.g. for all source points I have an attibute of say f@My_Emission. The lowest value found for a point is 0 and say the max is 2.5.

So I would assume there is a fitting happening when I specify emitattrib of the POP Source Dop node to use @My_Emission and maps out 0 to 2.5 as 0 to 100% ?

Or do I have to set up my values beforehand to say 0 to 1 ?

Like I said I could probably test this out…but since I'm not too experienced using DOPs I'm not sure the results I see is all there is going on.

Yes, in that mode you can think of it as automatically normalized to result in total density of 1 if you will, it simply has to distribute the same amount of points so only relative “densities” matter to determine how many points each polygon gets, exactly the same way as Scatter Sop works when enforcing point count

Thank you Tomas.

Although it wasn't my intent, since I was just interested in controlling with the emission attribute where in the geomtetry points get generated or not ( I'm using two different POPs for the same geometry source to play with combining their results ).

From what your saying here and what you already said earlier to the other poster (if I understand correctly);

It looks like I could use that as a way to push/pull point generation from certain areas giving a build up or ‘dispersed’ effect;

Since the same amount of points will be generated, overall.

Will have to do another scene setup with that insight and see what interesting things I can do.

Thanks again.