vdb to poly topology

[meeotch]

So a buddy of mine swears up & down that there's a built-in way (as in a checkbox somewhere) to round-trip from polys to vdb and back to polys while maintaining the topology of the polygons in areas where the vdb hasn't changed from the original shape.  I've tried twiddling every button and slider on the Convert VDB node (with the original geo as a reference surface in the second input), and I can't get anything out other than the "quilted" converted VDB topology we all know and love.  (See attached file, wireframe mode.)

So my question to you, the collected houdini cognoscenti, is this:  which one of us is smokin' the crack rock?

polytovdbtopoly.hip

[woodenduck]

Best I can do is with an extra group, dissolve and fuse sops. Worth a shot!

polytovdbtopoly_v02.hip

[meeotch]

Thanks for the reply.  That does seem to work for the simple example.  (Though you can break it pretty easily - for instance, by turning up the frequency on the sphere.)

My guess is that if this function does exist somewhere in the built-in nodes, it would involve some relatively dark magic.  Seems like a difficult problem, in the case of arbitrary geometry.  Even once you identify more or less which areas are close enough to the reference geo to be considered "the same", you've still got the task of joining it in a reasonable way to the parts that don't match.  Or I guess you could loop through the reference geo and tag points in the vdb-generated mesh that are within a certain tolerance of 1) the reference polys and 2) reference points.  The dissolve away 1, while preserving 2.  Still doesn't guarantee you edges in the same place, though.

Anyway, I guess this functionality isn't built-in, then?

[edward]

I think in theory that sounds like it might be possible but it's not in any publicly released OpenVDB tools that I know of. Does your buddy work at DreamWorks by chance?

[meeotch]

Nope - Bluesky.  So it's entirely possible that it's an in-house mod.  (My buddy is sharp enough to know the difference - but he did make his claim from memory, he wasn't at work.)

[magneto]

Regardless can we have this feature in Houdini please?