Hello,

I'm wondering if there is a way to delete part of a fog volume like you can with regular geo or with a vdb combine. I have this smoke that is colliding with an imaginary back wall, it's helping give a nice shape to the smoke for the effect that I'm after. As it's sliding down the back wall I'm getting some funny artifacts that I'd like to get rid of. Ideally I'd like to create a very thin region with a box that can delete those areas right at the back.

See artifacts here. Hey are extra noticeable in motion.



Here is the info of the object.




I've searched for a resolution to this but have not found anything. I'm open to any suggestions and resimulating if I need to.

Cheers!

Hey,

I'm not sure if I understand your question correctly, but if you want to create a kill box in your scene to kill parts of your fog volume, I'd set up an SDF kill box, and run a couple of lines of vex to make the density of your fog volume 0 where the SDF is <= 0. I'll attach a picture showing the results and the vex code. (The VDB from poly node on the right should have the name "make_sdf".)



Hope this is what you were looking for.

Yes that did the trick thank you!

This does not reduce the size of the fog vdb if i export to say blender right? the volume is all there just the density set to 0 and we can't see it. Like setting @Alpha on a mesh in houdini.

so this is not "Delete" rather "hide"?

FJSam
This does not reduce the size of the fog vdb if i export to say blender right? the volume is all there just the density set to 0 and we can't see it. Like setting @Alpha on a mesh in houdini.

so this is not "Delete" rather "hide"?

yes, but all you need to do to then "delete" empty voxels (or within tolerance) is append VDB Activate SOP set to Deactivate