Blocky Karma Pyro [SOLVED]

[GlennimusPrime]

Hello! I have a very odd issue with cubic-like blocky patterns appearing in the dense parts of my pyro volume. (This is the indirect emission AOV, as it shows the issue most clearly)


Unfortunately I'm unable to post a .hip file due to the project NDA.

Some details about my setup:

• Houdini 19.0.531 - Same issue using both Karma and Karma XPU
• To get a sense of scale, the explosion takes up about half HD frame size with a voxel size of 0.005
  Pretty small voxel size for something of this scale. You can see the bottom half of the explosion seems to hold up to resolution.
• I'm using the SOP Pyro solver
• I'm exporting as 16bit float VDB with a resampled velocity volume (although the same issue appears when not resampling and also un-checking 16bit float export).
• I'm using the Pyro Bake Volume SOP to visualise and apply the Pyro material

The only thing that stands out to me as an issue could be the density ranges coming out of the sim are between 0.5 and 1, but the Pyro Bake Volume SOP is pushing this density up to 75 to render.
Is this sort of density level something I should try to achieve directly out of the sim, rather than pushing these density levels up post sim?

I'm basically using the default render settings, as the issue persists when playing around with various settings.
Volume limit is set to 1, as the density of the volume is being lit from an emissive background object (the issue remains when using a normal point light instead).

 

 

 

 

Edited October 3, 2022 by GlennimusPrime
remove unnecessary images

[Atom]

That's exactly right. Your images show what happens when you push density too far and completely fill each voxel to the maximum density value. Push density at the simulation level, not after the fact at render time.

Edited September 29, 2022 by Atom

[MENOZ]

it seems to me it's not a problem of voxel density but of the simulation itself. voxels looks to be smaller than your blocks as i can see smaller scale details, also the shape of that mushroom is weirdly geometric. it looks like you are using sparse pyro, you might need to increase the padding or try to use the option "extrapolate velocity into new tiles". 
https://www.sidefx.com/docs/houdini/nodes/dop/smokesolver_sparse.html#sparse_streakvel

[GlennimusPrime]

On 10/1/2022 at 9:40 AM, MENOZ said:

it seems to me it's not a problem of voxel density but of the simulation itself. voxels looks to be smaller than your blocks as i can see smaller scale details, also the shape of that mushroom is weirdly geometric. it looks like you are using sparse pyro, you might need to increase the padding or try to use the option "extrapolate velocity into new tiles". 
https://www.sidefx.com/docs/houdini/nodes/dop/smokesolver_sparse.html#sparse_streakvel

That was it! Thank you so much for this info. Had been banging my head for a few days on this one.

Always something new to learn!

[demoncase]

On 9/30/2022 at 5:40 PM, MENOZ said:

it seems to me it's not a problem of voxel density but of the simulation itself

this phrase saved me

my simulation was blocky at the edges, but I was using a low value at the volumerasterizeattributes (voxel and particle size) and also in the volume source inside the dop, the temperature mode was set to add, changed it to maximum!
the blocks stopped 

[brencaaa]

On 9/30/2022 at 10:40 PM, MENOZ said:

it seems to me it's not a problem of voxel density but of the simulation itself. voxels looks to be smaller than your blocks as i can see smaller scale details, also the shape of that mushroom is weirdly geometric. it looks like you are using sparse pyro, you might need to increase the padding or try to use the option "extrapolate velocity into new tiles". 
https://www.sidefx.com/docs/houdini/nodes/dop/smokesolver_sparse.html#sparse_streakvel

Thank you for this! Tried everything I could think of and didn't solve the issue (that btw is a common one, at least for me), but this did the trick. Again, thank you!