VDB From Polygons

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VDB From Polygons

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The VDB From Polygons allows you to create a VDB volume based off of the shape or attributes of an object.

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    If you're new to VDBs, then please check out the VDB lesson at Houdini For the New Artist II first.  This node has two inputs - the first one is for the incoming geometry and the second one is for any reference vdb that you may have.  What the reference VDB will do is determine the voxel size/resolution of your vdb.  Be sure to also use the volume slice sop along with viewport visualizations to preview the voxel values.

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Main Parameters:

Voxel Size:

--  This determines the quality of your vdb volume.  Lower voxel size = higher quality.

Reference VDB:

--  If you plug in a vdb to the second input and there are multiple vdb fields going into the second input, then this parameter allows you to select which field you'd like to use for determining the resolution.

Distance VDB:

--  The Distance VDB is also referred to as an "SDF Volume."  The the distance from the surface of the object is measured and the values are then stored inside the voxels surrounding the surface.  If you turn up the exterior band voxels parameter, then you are telling the distance vdb node to measure further away from the surface.  If you turn up the interior band voxels, then you are telling the distance vdb to measure further inside the object.  By default, any values inside an object will be negative.  Any values outside the object will be positive.  Remember that it's very important to make sure that your mesh does not have any holes, overlapping faces, and correct normals.

Fog VDB:

--  Fog VDBs will populate voxel values inside the mesh with a value of 1 by default.  The "Interior Band Voxels" will feather out the values from the surface.  As an example, if the interior band voxel is 3, then that is saying, "It takes 3 voxels in order for the value to fully reach 1 as you're going inside the mesh."

Exterior/Interior Band Voxels + Use World Space for Band:

--  These parameters will have a different effect depending on whether or not you've selected "fog" "distance" or "surface attributes."  For more information about what each mode does, visit those respective sections.  If you check on "Use World Space for Band," then that will use meters instead a specific number of voxels to determine the distance away from the surface.

Fill Interior:

--  For Fog Volumes, the fill interior will cause the center of the object to be a value of 1 and all other values to gradually fade to 0 as they approach the surface.  For SDF Volumes, it will remove the "Interior Band Voxels" parameter and guarantee hat each voxel inside the mesh measures the distance from the surface.

Unsigned Distance Field:

--  This only works when you're generating an SDF Volume.  Instead of voxel values going negative as they go inside the mesh, they will be positive.  It's like taking the absolute value away from the surface of the mesh.

Surface Attributes:

--  This section allows you to populate voxel values based on point/prim/or vertex attributes.  Be sure that you specify what kind of attribute you'd like to sample from by using the syntax:  "point.foo"  The exterior band voxel parameter will extend the value inside and outside the mesh by a certain number of pixels, (or by a certain distance in meters if world space for band is turned on).