OpenVDB is an open source hierarchical data structure for volumes. It has become the standard for interchange of volumetric data between applications.  For more information about OpenVDB, see the OpenVDB FAQ .

Houdini 16.0.655 onward

Rendering from an OpenVDB File

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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.

Modifying VDB

Houdini has a list of VDB SOPs which allow us to modify the VDB data to render.  For example, say we want to only include the density grid name for the render,  we add a VDB SOP.  

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Then specify the density name and its type.  In this example, it is called "render.density".  We can also add more than one name to include.  We can also enable or disable them.  

See http://www.sidefx.com/docs/houdini/nodes/sop/vdb for more information.

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Rendering from Houdini Volume

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Before Houdini 16.0.655

Rendering from an OpenVDB File

If you already have a .vdb file, RenderMan will read it with blobbydso:impl_openvdb procedural without converting the .vdb file to volume.  Before Houdini 16.0.655, the only way is to create a box SOP and manually specify the Post include to inject it to the RIB.

Using Post Include

Create a box OBJ. In the box's Render/Geometry's Obj post-include, include the RiVolume that will be emitted to the RIB.

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For example:

Volume "blobbydso:impl_openvdb" [-19 19 -7 80 -18 80] [0 0 0] "constant string[2] blobbydso:stringargs" ["$HIP/vdb/smoke.vdb" "density"] "varying float density" [] "constant float blobbydso:threshold" [0.001]

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