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See volumes for an explanation of standard volumes and OpenVDB volumes.
The input geometry must be a quad or triangle mesh. This node will "convex" the input surface into such a mesh if it isn’t.
This node can create a distance field (signed (SDF) or unsigned) and/or a density (fog) field.
When you create a fog field you can choose to fill the band of voxels on the surface or (if you have an airtight surface) fill the surface (see the Fill interior parameter).
Since VDB primitives only store the voxels around the surface, they can have a much a higher effective resolution than creating a traditional volume with IsoOffset.
You can connect a VDB to the second input to automatically use that VDB’s orientation and voxel size (see the Reference VDB parameter).
The size of voxels in the output VDB volume. Surface features smaller than this will not be in the output VDB.
If the second input is connected, you can enter the name of a VDB primitive in the second input to copy the orientation and voxel size from it.
See specifying volumes.
Creates a signed distance field (SDF). An SDF stores the distance to the surface in each voxel. (If the voxel is inside, the distance is negative.)
Creates a density field.
Voxels in the band on the surface store
1 and voxels outside store
The size of the filled band is controlled with the Interior Band Voxels.
Turn on Fill interior to create a solid VDB from an airtight surface instead of a narrow band.
You can generate additional VDB primitives that store the values of primitive (face), point, or vertex attributes. Only voxels in the band around the surface will be set.
The name of point, vertex, or primitive attribute to create a VDB from.
A new name for the generated VDB primitive storing the attribute values. Leave this blank to use the attribute name.
How vector values should be interpreted.
Use World Space for Band
Sets whether Exterior band and Interior band are specified in Houdini units. When this option is off, the band width parameters are in voxels.
Exterior Band Voxels
How many voxels outside the surface to fill in the generated VDB (when Use world space for band is off).
How many Houdini units outside the surface to fill in the generated VDB (when Use world space for band is on).
Interior Band Voxels
How many voxels inside the surface to fill in the generated VDB (when Use world space for band is off).
The distance to compute the distance field inside the mesh.
In SDF mode, Fill Interior extends the signed value all the way to the middle of the volume. In Fog mode, a gradient is applied from 0 at the surface (0 values of the SDF) to 1 at the innermost distance of the SDF Field (the most negative SDF values).
Unsigned Distance Field
When creating a Distance VDB, simply store the distance from the voxel to the surface (no negative values). This avoids trying to figure out inside and outside, so the surface doesn’t need to be airtight.
This is similar to the Minimum function of the Iso Offset SOP.
Polygonal mesh to convert
The polygonal surface to convert.
Optional reference VDB
If connected, this node copies the orientation and voxel size from a VDB primitive in this input.
The following examples include this node.
This example demonstrates how the Gas Equalize Volume dop can be used to preserve the volume in a fluid simulation.
This example demonstrates keyframing the internal grains of a solid pighead to create an animated puppet.
This node shows how to iterate over all the pieces of one geometry to consecutively subtract volumes from an original geometry.
This is an advanced example of how to use the FindShortestPath SOP to prefer "central" paths, based on centraily measures computed using FindShortestPath and AttribWrangle. This helps avoid staying too close to walls where avoidable.
Turn on the Display Option > Optimization > Culling > Remove Backfaces to see inside the space more easily. Try visualizing the different centrality measures using the switch node. The same example without considering the centrality of the path is demonstrated in a side branch of the SOP network, in order to see the difference.