VDB export not working

[Muadeeb]

i am using max 2017 and phoenix fd - 3.18 latest may build.
unit scale meters.

exporting vdb´s is not working. the sim gets saved out but the vdb sequence files themselves are entirely black - like the density is maxed out.
lowering density to its lowest possible value make the sim visible but the whole containers is still visible too.

i tried rendering in c4d octane, houdini clarisse, aswell, as native c4d r20 vdb import.

this only happen with fire sims. liquids get saved out well as vdb, obviously i would not need that.

i tried contacting support, apart from the boilerplate answer no reply whatsoever.

[Svetlin.Nikolov]

Hey,

So the most important thing to note is that cache files contain only the raw simulation data. Render settings are specific to the software you are using since each renderer is different. This is why they cannot be written to cache files. If software defaults don't work, you have to equalize the render settings manually knowing how the software's renderer works. This is a valid rule for any fluid simulation software, not just Phoenix.

If you are transferring aur, vdb or f3d grid cache files between Phoenix and V-Ray integrations in Max, Maya, Cinema, etc, you have to equalize the render settings after you load the cache file - all of the options under the Rendering rollout and the Volumetric Settings. Phoenix and V-Ray can exchange render presets via preset files that you can save and load from the top of the Rendering rollout of Phoenix or the V-Ray VolumeGrid.

However, if you are loading the cache data into another software, you need to have knowledge of how the render settings of the software work, so you can manually equalize the settings if defaults don't work. Liquids, as you pointed out, are pretty straight-forward and come down basically just to density. The Large Smoke toolbar preset of Phoenix simulates only smoke so it also comes down just to density. The explosion toolbar presets have temperature and smoke density written to the cache files, and in that case you have to watch out since the smoke goes from 0-1, but temperature in Phoenix is in Kelvins so it ranges from about 300 to 2000-3000, unlike many other fluid simulation software where temperature is in non-physical units so it can range from 0-20 or -50 to +50 and such.

The Fire preset you are using has only Temperature simulated and the fire color, fire intensity and opacity are all based on the Temperature channel. You can have a look at how they are set up int he Volumetric Options dialogue under the Rendering rollout.

You can find out more about how Phoenix rendering works here: https://docs.chaosgroup.com/display/...moke+Rendering;
Here are some handy tips and tricks, including tips on how to equalize render settings with other software: https://docs.chaosgroup.com/display/...ips+and+Tricks
Here are some advanced tips on rendering: https://docs.chaosgroup.com/display/...ering+In-Depth
And finally - if Support is overwhelmed at the moment and cannot respond to you quickly, please feel free to post here in the forums or in our facebook group where the dev team and many experienced users can help you as well: https://www.facebook.com/groups/233735903483447/

Cheers!

[Muadeeb]

hi svetlin,

i appreciate the thorough reply. after i browsed the forum i realized that the support is overwhelmed and that my waiting is not unique.
nonetheless i had to resort to an alternative plugin for the specific project but would like to solve this for the long run.

before i get into the troubleshooting of rendering settings, i´d really like to be certain this is not some bug or user error while simulating.
before contacting support i have tried using the data channels to drive the rendering within octane, it made no difference.

why i dont think this is a render issue is, like i mentioned. the problem occurs in viewport aswell, both in houdini and c4d.
this is a c4d screenshot:

to the left is the phoenix vdb, to the right is a fume fx sim.
they are different sim objects (one is ring the other a quick sphere) but you can see the issue.

i am uploading the vdb aswell, so if you can be so kind and take a look at it, i´d be very grateful.


cheers,

[Svetlin.Nikolov]

Ah, yes - the reason for this is the Temperature grid channel which is in Kelvins. Room temperature in Kelvins in around 300 degrees. In Phoenix, if your fire/smoke simulation sources emit temperature above 300, it rises up, and if the temperature is below 300, the fluid falls down instead, so this way you can simulate dry ice, etc. By default empty grid voxels are filled with Smoke = 0, Fuel = 0, black RGB, and Temperature = 300, which means neither hot fluid, nor cold, so it won't cause the solver to create upwards or downward movement.

In this simulation cache the temperature ranges from 300 to 2000 and it's a very good example for how the Cache File Content info box under the Simulation rollout is supposed to show the ranges of the grid channels in the loaded cache for the current timeline frame. With AUR cache file the temperature range is shown correctly, but using your cache I just found out that VDBs incorrectly show the temperature range as 0-2000 instead of the expected 300-2000. We will fix this ASAP in the Phoenix nightly builds.

Probably other software assumes that the grid data always includes the 0-value, and this is why the empty space in the simulation grid where the Temperature is 300 also shows up in the preview or rendering. What you can to do work around this is to specify an offset of 300 in the render settings of the renderer you are using. I'm looking at Octane right now and though there is a Scale option for emission, there is no offset, so maybe you need to use an Emission ramp.

In Phoenix and the V-Ray VolumeGrid this empty space does not show up because the default Emission remap looks like this and all voxels with Temperature below 800 are ignored from the rendering by default:

[Muadeeb]

thanks svetlin,

very nice of you to chime in so early in the morning, i appreciate it.
i will see if an emission ramp can alleviate this, looking forward to that nightly aswell.

regards,

[Svetlin.Nikolov]

Hey, my pleasure - one more thing that comes to mind is that Octane in Max can render Phoenix volumes natively by just putting a modifier over the Simulator, so there must be a way for Octane to add this offset to the data internally, though I can't find an easy way to make it work without the ramp.. I hope I have overlooked it and there is a simpler way to do it, but if there isn't, we gotta rethink the temperature data range in Phoenix vdbs so it won't cause so much extra work when importing in other software...

[Muadeeb]

good to hear that you have taken this issue onboard.
since you mentioned natively rendering with octane, i have to ask on an off-chance:
any possiblity of having phoenix ported to c4d at some point? i realize this is a massive task, just wondering since i am firing up 3ds max only because of the couple of plugins.
their (adsk) subscription rollout was beyond insulting and the final straw for me. very glad to have jumped ship fwiw and i am sure i am not the only one to have done so.

[Svetlin.Nikolov]

Oh yes, it's going to take a lot of work, but with time the more we improve out internal architecture, the easier would be to take the step from 3ds Max and Maya into any other host.

[Muadeeb]

good to know svetlin,

thanks.