Splotchy Fog with Phoenix FD Grid

[olika]

Hi lovely Phoenix Team

Another day another thing to solve haha

Please take a look at the attached screenshot.
It's a fairly simple scene, just a vray light with a texture on it, put inside a phoenix grid and used the smoke opacity method to create the fog.
It all works fine till some point in the animation where it seems a specific distance has those splotches which you can se in the picture.

I tried pretty much all Settings regarding quality etc. I.e. Cell size, Step%, LC Speedup and none seems to have any effect to this artefact.
The only thinng which changes something is making the cell size smaller, although the artefact will only also become smaller but still present. Decreasing cell size, At a certain cellsize the light dissapears comepletly? hm no clue

Would be great if you can point towards some direction.. Thanks in advance as always!

[olika]

Here's a gif to demonstrate what happens in the animation.
What i don't get is, it's fine at a very close distance and it's fine again going farther away but somehow in this middle part the fog goes nuts?

[georgi.zhekov]

Hello,

Can you send us the scene so we can check it out?

Which versions of Phoenix and V-Ray are you using? You can check the versions here - https://docs.chaosgroup.com/display/...entEnvironment

Thanks!

[olika]

hi georgi.zhekov thanks for reply! Sure, it's already in the first post, professionally hidden direct under the picture haha
Latest Vray and Latest Phoenix 4
*Update: With the env. fog i was able to do it now, but yeah, ugly ugly rendertimes compared to the phoenix fog method. But somewhere the speed must come from so maybe it's a limitation of the phoenix grid method?

[Svetlin.Nikolov]

Hmmm, you said you tried the LC speedup, but what about turning the Volume Light Cache off completely? This looks related...

[olika]

when i uncheck the light cache, even though the rendersettings are without any GI, the renderprogress comes to a grinding halt. I mean after 5 minutes there's not a bucket moved...hmmm maybe that is theoretical right i didn't even had the patience to wait for a test render hihi

[squintnic]

I have had so much trouble with this and the answer is always unacceptable render times and using volumetric geometry for phx
Surely havign a smoke sim rendering inside a hazy volume / fog is not impossible and quite a common situatuion - imagine a burnout from a car with a smoke sim but its in a hazy car park with volume lights from headlamps and street lights...

[Svetlin.Nikolov]

Ah this is different though - it's only one Phoenix sim made to look like fog. I would recommend replacing the fog with this exact same simulator setup if you have fog and Phoenix at the same time though.

Unfortunately not being able to blend separate atmospherics is a legacy from 3ds Max where atmospheres are simply laid on top of each other and do not blend - this is why their order in the atmosphere list matters. In V-Ray GPU the concept of an atmosphere no longer exists, so just recently blending a grid volume with env fog became possible - check the V-Ray 5 beta and use a volume grid or compatible Phoenix...