Hi

Does anyone Know how to expand houdini native volume directly as vdb does using VDBreshapeSDF sop. For now I can only figure out two indirect methods.
1 use peak sop to expand the polygon based on normal then convert it into volume use isooofset.
2 convert polygon into VBD then use vdbreshapeSDF to expand the VDB then convert back to volume.
Is there any way to do the same thing directly in volume?
I've used the volume active sop but eventually it only expand the bbox not the volume itself~

assuming your volume is proper SDF and there is enough padding for the expansion you can just easily do Volume Wrangle

@density -= chf(“offset”);

where “density” is the volume name or Bind Each Volume To Density is checked
and “offset” parm will be uniform offset to expand/contract the surface

or Volume VOP to do the equivalent, of course in both cases you can control that using noises, other volumes, etc.

or if uniform expansion is what you are after you can as well use Volume SDF SOP and tweak the Iso Surface Parm

Thank again for your detailed reply.
I figured out that because of the SDF have the signed distance field for direction.However,if I only build a fog volume using a isooffset sop from a pighead, How can I make it expand or subtract when it lacks the direction message?
Any way, It seems to me that you know everything about houdini and I do appreciate your hlep.