Vray environment fog and Phoenix smoke

[georgi.zhekov]

You should be able to load the VDB with Phoenix without a problem and get the exact same result as with the Volume Grid.

[Svetlin.Nikolov]

Ah, dang...but I should be able to render the houdine VDB via a phoenix grid, instead of the volume grid, which I´m doing now, right?
Just gonna try it out...

Indeed, phoenix grids get combined with other Phoenix grids in the same atmosphere, and vvgs get combined with other vvgs too.

[ben_hamburg]

Yes, I just tried it out, works perfectly now!

[ben_hamburg]

Ok, just a quick follow up, I got the whole houdini VDB sequence now and its all working in theory. Unfortunately some frames can´t be rendered and give me vray unhandled exceptions.
I´ll start troubleshooting as soon as I got time for that, starting by replacing the phoenix grids I use now to replace Environment fog and load the houdini VDB with VrayVolumegrid.
But maybe you know of some Issues that could come up when rendering houdini grids?
For example, for cache size reason we left out the velocity channel in the vdb and chose not to render that with motion blur.
It might also be an error with houdini vdb export, so we´ll look into that as well.

[George Barzinski]

Maybe you can try to render single cache with single volume grid and see will it crash or not.

[Svetlin.Nikolov]

You definitely shouldn't get crashes though - if you could send over a scene that reproduces those, it would be very helpful to track down the issue,

Cheers!

[ben_hamburg]

Hm seems like I could pinpoint the issue: I´ve consistently had one frame crash when camera motion blur was disabled, but it worked when motion blur was enabled. I get an error message then, saying that there is no velocity in the grid 8which is why I disabled motion blur in teh first place), but it renders. In this case this would work fine, since the houdini vdb is very slow moving and camera motion blur in that part is also barely noticeable.

I will try and strip down the scene and see if it still crashes, if the problem persists and if so I can send you the scene.

[ben_hamburg]

Ok, false alarm...stripping teh scene down also got rid of the error, so it must be somewhere else in the scene.

[Svetlin.Nikolov]

Ah, whew! Thanks for taking the time to help catch this though!

[ben_hamburg]

haha, well, its not like I´m not interested myself in figuring it out...
there is just always soo many variables, but I definitely got better at troubleshooting. Still haven´t figured out whats causing it though, rendertimes are so high even though I already reduced settings and size dramatically and it always crashed seemingly randomly sometime during the render.
I´ll let you know when I figure it out, in case its reproducible (be it phoenix or Maxs fault...)

[ben_hamburg]

Ok, I figured it out, it didn´t have anything to do with phoenix or vdb, the problem was with a vraySSS material in refractive mode.
I´ll report it in the Vrayforum...

[Svetlin.Nikolov]

Great job! Hope it's one less issue soon then..

[ben_hamburg]

Alright, I'm back. Again, everything seems to be working, but I can' t get render times in an except able range...hovering around 4 hours now.
It mostly seems to be because of the houdini VDB.
I noticed, that the Y-range (to the right side) is between 0 and 15,while with Phoenix it's always between 0 and 1.
So I'm guessing it still has too much transparency, which, combined with high voxel count always seems to be a render time killer.
I think I'll try and send you a stripped down scene, maybe you could figure out a way to speed things up.

It's probably not possible, but having the light cache speedup work with vraylight elements would also be great...

[ben_hamburg]

Did some more testing and the problem isn´t the houdini grid, its the environment fog (through an empty grid with opacity curve).
And more specific, it was because of one light.
It seems my setup doesn´t like very bright lights.
To get some god rays in the background, I placed a small Vraysphere light and because it was so dark, I increased the multiplier to about 30.000.
When I did the troubleshooting, I tried disabling the shadow and the result was very very bright, so I figured that the bright light was "battling" with the environment fog and that caused the high render times.
So instead I increased the size of the light and massively decreased the intensity and that cut rendertimes to 1/5th...

[Svetlin.Nikolov]

We are working on the VRayLightSelect + Phoenix Light Cache as we speak

Indeed, having smoke more opaque is a very big time saver - try to rescale the opacity. Are you using a curve, or just Simple Smoke?