Ring artifacts in VDB Smooth SDF

[melazoma]

Hi all,

I'm in a bit of a pickle, and it'd be great if anyone can offer some insight on this.

I have a FLIP sim being meshed with the new VDB meshing workflow, and I am getting a ringing pattern in the vdb sdf volume after the vdbsmoothsdf operation has been applied.

I am trying to get rid of the ringing as it is passed onto the mesh resulting from convertvdb and ends up in the final render.

The FLIP sim used a Particle Separation of 0.3 and resulted in ~1.3 million FLIP particles packed tightly in a 4x4x4 unit (meter) space with no open holes, etc.

The VDB SDF Smooth operation uses Gaussian with filtering voxel radius = 2 and iterations = 4. This is meant to be a very smooth liquid--like hot chocolate.

The results from other smooth methods (Laplacian Flow, etc) were not smooth enough.

I have tried to increase the smooth radius and iterations, but it seems the more I increase these values the ringing gets worse.

I also tried to set vdbfromparticle above vdbsmoothsdf to over-sample by reducing Voxel Size to 0.006 (instead of the default 0.3/2 = 0.15),

and then turn up the smoothing. This made the ringing significantly finer, but the artifact still remains visible in the smoothed sdf.

I'm sorry for posting all this details without a hip file. I will try to post an isolated example tomorrow as I only have the production file at the moment.

But has anyone run into this problem in the past or is dealing with it right now? Thanks in advance for any help offered.

[Nerox]

I've / am facing the same challenge, I found that adding a bit of Adaptivity (ability to use less polygons where necessary) on the convert VDB sop makes a world of a difference. It appears that the amount depends on the resolution you're working with. Lower resolutions need more adaptivity the higher resolutions. This can add some artifacts so adding a smooth afterwards helps as well.

[melazoma]

I've / am facing the same challenge, I found that adding a bit of Adaptivity (ability to use less polygons where necessary) on the convert VDB sop makes a world of a difference. It appears that the amount depends on the resolution you're working with. Lower resolutions need more adaptivity the higher resolutions. This can add some artifacts so adding a smooth afterwards helps as well.

Hi Nick, thank you for the tip on iso-adaptivity. While the rings have not completely gone away, I was able to make it less obvious by setting it to 0.001.

Edited April 2, 2013 by melazoma