create mask for vdb to limit noise area in volume vop

[anicg]

I have an vdb (sdf) to which I apply some noise in a volume vop. The noise is applied everywhere. I need it to be limited to some areas, so I need to create a mask. The mask can be driven by a noise.

Is it possible to create a mask for a vdb?

P.S. the vdb was a polygon geometry, would it be an option (and how) to use a mask from polygon into vdb? whichever way exists and works 

Edited July 7, 2020 by anicg

[evanrudefx]

Here is an example using curveu point attribute as a mask to limit noise.

vdb_mask.hiplc