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Different result from volume in bifrost exported as vdb in arnold

Message 1 of 9
231 Views, 8 Replies

Different result from volume in bifrost exported as vdb in arnold

Hello everybody ! 

 I have an issue with an export of a volume made in bifrost graph as a vdb file. I made a compound that makes a volume from a mesh with the node mesh_to_volume that I multiply with a fractal field to add more details in it. When I try to render it, every thing works fine :



Then I made an export as vdb with the node write_OpenVDB and it worked fine. I can read it in my bifrost graph with the node read_openVDB_volume but when i try to open it with an arnold Volume in a different scene, it seem that the volume has lost a lot of definition and I don't konw why. 



Does any body have an idea how to read it properly with an arnold volume ?  Thank you in advance 🙂 




Message 2 of 9
in reply to: brunoalive

What was the resolution setting for the voxel? And for the ai Volume Shader, do you add that post cache or pre-cache?

Message 3 of 9
in reply to: Polytikal1

for the voxel size in bifrost: 

the detail size of the mesh_to_volume is 0.05 in absolute

the detail size of the volume_to_mesh is 0.05 in absolute 


in arnold I didn't find any voxel size param 😕 




and for the volume shader I add it after I done the cache

Message 4 of 9
in reply to: brunoalive

Can you share the scene, it will be easier to help. It should not happen but I cant tell for sure why is happening without looking at something. Out of curiosity why are you rendering outside BF?  You know you can create a volume material inside the graph as well, right? 



Message 5 of 9
in reply to: sepu6

yes sur !

I made a little project folder with the scene and the abc I used to do the fx in bifrost :


I want to export it as vdb because i want to use it in an other scene. I am working on a sequence to render and I didn't want to add a bifrost graph in it because it will increase the size of the scene. 

Message 6 of 9
in reply to: brunoalive

There is a small difference between the VDB and rendering straight from BF but nothing like what you are seeing. 

That small difference is probably because of the resolution rounding that BF volumes have to do when you convert them into VDB. 

What version of BF and Arnold are you on? 


Arnold Volume  (VDB)


BF - ReadVDB 



BF no VDB, direct output



Here is the file 

Message 7 of 9
in reply to: brunoalive

Thank you for your help ! 

I'm on maya 2023.1, bifrost, MtoA 5.1.2

Message 8 of 9
in reply to: brunoalive

I would upgrade to 2.6 and the latest Arnold as well. It is a much better experience overall. It also could be a bug in that version, but I do not recall. 

Message 9 of 9
in reply to: sepu6

Alright I see where I was wrong, I didn't set the Density Chanel as voxel_fog_density in the AistandardVolume. It was by default on density. I checked your options in the scene you provided and it was the missing step.  Thanks a lot, you are the boss 🙂 !!! 



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