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Negative temperature values when render "temperature" image pl

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   Hello everyone!


   I need temperature values render pass for some post compositing purposes from Pyro simulation.

When I'm rendering it as "temperature" float 32 pass, I'm receiving negative values near the borders of volume. Why does it happening? Attaching picture.

I can normalize this somehow after render, but I want to now why it is that way. There is dead end node "Fit Range Unclamped"(picture attached)  in default shader(Fireball in this case).

I can pass "temperature" parameter through some "fit ranges" or even "Reshape" node. But it doesn't answering the question Why? And I don't think that is the right way.


   Should say that remapping from shader tab from shades hasn't worked properly for me - even with clamping and fit set for 0 - 1 there was negative values and values bigger than 1.


   Basically, I need normalized (from 0 to 1) temperature render pass for my simulation. 


   Maybe someone can help my with this?

Will be much appreciate. 


Attaching 2 screenshots. Don't attaching .hip file because there is a simple sphere with Pyro Explosion shelf preset on it.


   P.S. Don't want to make another post right now, so should ask - is anybody know proper way to make a vectorfield texture from Pyro Sim in Houdini? Right now I'm using Volume Slice, rendering remapped normalized (from 0 to 1) motion vector pass from top orthographic view and compositing it in kind of flipbook, which is converted into volume texture dds next. Maybe there is another way to do it? 


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for temp, just use a volume wrangle and max it with 0.


"f@temperature = max(f@temperature,0);"



i noticed the same thing the other day.  i suspect it's some kind of mathematical artifact.

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Fathom, thank you for answer!


Your method is working propertly, of course. Basically, better than mine previous normalizing to only positive on comp stage. I think you're right about mathematical artifact, so I won't to dig it anymore. It's just working fine.

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