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In Houdini 16.0.655 onward, we simply create a Geometry SOP. Dive inside the node and set the File SOP's Geometry File parameter to point to  your .vdb file. That's it! RenderMan for Houdini will automatically detect the bounding box and all the VDB grid names.

Assign PxrVolume or your volume Bxdf to the Geometry node. Don't forget to set the density primvar name (which matches the density grid name in your .vdb file) appropriately in PxrVolume.

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