Houdini 20.5 Nodes Geometry nodes

VDB from Particles geometry node

Converts point clouds and/or point attributes into VDB volume primitives.

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Since 12.5

See volumes for an explanation of standard volumes and OpenVDB volumes.

This node can create a distance field (signed (SDF) or unsigned) and/or a density (fog) field.

Since VDB primitives only store the voxels around each point, they can have a much a higher effective resolution than creating a standard Houdini volume.

Note

This node uses the point scale attribute (pscale) on the input points to convert them to spherical densities. This attribute is set by the Attribute POP or the Point SOP.

If points are smaller than 1.5 voxels, they cannot be resolved and will not appear in the VDB.

You can also scale all sizes using the Point radius scale parameter.

You can connect a VDB to the second input to automatically use that VDB’s orientation and voxel size (see the Reference VDB parameter).

Parameters

Voxel Size

The size of voxels in the generated VDB volume primitive. Points smaller than this cannot be resolved by the VDB so will not be in the output.

Reference 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.

Distance VDB

Create a distance field VDB, where each voxel stores the distance to the nearest point.

Fog VDB

Creates a density field, where a voxel is 1 inside a point (that is, the sphere centered around the point with radius defined by the point’s pscale attribute), and 0 outside.

Mask VDB

Create a mask field VDB.

Generate an alpha mask that is very useful for subsequent constrained level set smoothing of the level set surface from the particles. This alpha mask is defined as the fog volume derived from the CSG difference between a level set surface with a maximum radius of the particles and a level set surface with a minimum radius of the particles. This mask will guarentee that subsequent level set smoothing is constrained between the min/max surfaces thus avoiding the problem that surface details can be completely smoothed away.

Point Attributes

You can generate additional VDB primitives that store the values of point attributes. Only voxels near the points will be set.

Attribute

A point attribute to create a VDB from.

VDB Name

A new name for the generated VDB primitive storing the attribute values. Leave this blank to use the attribute name.

Vector Type

How vector values should be interpreted.

Point Radius Scale

Multiply the particle size (pscale attribute) by this amount before converting.

Minimum Radius in Voxels

Points with radius less than this number of voxels are ignored. Points with radius smaller than 1.5 voxels will likely cause aliasing artifacts, so you should not set this lower than 1.5.

Prune

After building the VDB grid there may be undetected constant tiles. Enable this to detect constant regions and collapse them. This option only has an effect if the particles are larger then the leaf nodes so it is normally recommended to leave it disabled.

Mask Width Scale

Use this scaling parameter to adjust the width of the generated mask VDB.

Use World Space for Band

Sets whether Half-band is specified in Houdini units. When this option is off, the half-band parameter is in voxels.

Half-Band Voxels

How many voxels outside the point sphere to fill in the generated VDB (when Use world space for band is off).

Half-Band

How many Houdini units outside the point sphere to fill in the generated VDB (when Use world space for band is on).

Merge With Reference VDB

If a reference VDB is specified, the new particles will be unioned into that signed distance field. This allows one to use the particles to only specify the surface detail, but have a coarse, offset, grid used for the main bulk.

Particle Footprint

The shape of the densities created from points when Fog VDB is on.

Spherical

Create spheres centered on the point with radius defined by the point scale attribute (pscale).

Velocity trail

Create multiple spheres trailing off in the direction of the point’s velocity attribute (v). This may be useful for visualization.

Velocity Multiplier

When Particle footprint is “Velocity trail”, this scales the length of the trail relative to the point velocity attribute (v).

Velocity Spacing

When Particle footprint is “Velocity trail”, how far apart to space the spheres in the trail.

Inputs

Particles to convert

The point geometry to convert.

Optional reference VDB

If connected, this node copies the orientation and voxel size from a VDB primitive in this input.

See also

Geometry nodes