Houdini 20.5 Nodes Geometry nodes

Volume Rasterize Particles geometry node

Converts a point cloud into a volume.

Since 13.0

The Volume Rasterize particles operation takes a cloud of points and fills a volume accordingly. If the input volume has more than one named primitive, the named volumes will be filled with data from point attributes that match the name of the volume. Currently only VDB vector volumes support filling from vector point attributes.

The point attribute pscale is used (along with the specified Coverage Attribute) to control the generated volume.

This is a highly specialized node designed for filling the volume as fast as possible, so a lot of the controls present in Volume Rasterize Points are not available.

Filtering is automatically performed to ensure small particles will always contribute to the resulting volume. This means that when you rasterize to a particularly low resolution volume, things will seem to fatten.

The volumefilterstochastic integer primitive attribute can be used to override how points are filtered to voxels. For fields that can’t be meaningfully averaged together, setting this attribute to a value of 1 on that volume primitive will cause only one of the overlapping particles to contribute to each voxel, avoiding any averaging. This parameter only applies to fields other than coverage.

Alternatively, the stamping method for each volume can be controlled separately by specifying rules, bypassing the need to set primitive attributes.

Note

This node does not support rasterizing into tapered volumes.

Parameters

Destination

Which volumes or VDBs in the first input to stamp into.

Particles

A group of points in the second input to rasterize.

Filter

The filter shape to use when splatting particles. The default Gaussian filter will produce smooth blobs and is useful for larger particles. When the particle size is smaller than the voxel size, a box filter will produce a similar result in less time.

While most filters are designed to integrate over the voxel, the Cubic Spline Filter instead is designed for defining the value at the voxel center. This is useful for performing precise particle to grid transfers for APIC (Affine Particle-in-Cell) based algorithms. Weights on neighboring grid nodes depend only on the voxel size and their relative position to the particle, which are not affected by the coverage and scale attributes.

Coverage Attribute

Name of the point attribute that stores the coverage (or influence) of each particle. If the coverage attribute does not exist, each particle is assumed to have a coverage of 1.

Coverage Scale

The coverage attribute will be scaled by this value.

Particle Scale

The pscale attribute will be scaled by this value. If this attribute does not exist, 1 will be used as the reference.

Minimum Filter Size

If the particle’s radius is much smaller than a voxel, it can appear to pop from grid-location to grid-location as it moves. This adds an additional blur to particles to ensure they are this fraction of a voxel. A value of 1 ensures the main-support for each particle is at least a voxel, guaranteeing that any movement of the particle will correspond to a smooth change in voxel values, at the cost of less sharp boundaries.

Velocity Blur

Enables rasterization of velocity blur. Velocity blurred particles are rasterized by creating multiple point samples along the velocity path and distributing the coverage of the original point among these samples.

Shutter

The shutter time to use for velocity blur rasterization.

Shutter Offset

The shutter offset to use for velocity blur rasterization.

Blur Samples

The number of motion blur samples to use for velocity blur rasterization. Larger numbers of samples will produce smoother and more accurate results, but will take more time to compute.

Normalize by Clamped Coverage

Enabling this option multiplies the sampled volume by coverage, yielding a smooth transition between areas covered by the particles.

Note

This option changes the default stamping method from Weighted Average to Covered Average; Attribute Rules can be used to override this default behavior.

Attribute Rules

Rules that specify the stamping method on a per-volume basis.

Note

If multiple rules apply to a volume, the first one is used.

Note

volumefilterstochastic primitive attribute takes precedence over the rules. That is, Stochastic stamping will be used for all volumes that have a value of 1 for the aforementioned attribute. If value is 0, however, then the appropriate rule still applies.

Note

The Coverage Attribute is unconditionally stamped using the Accumulated method.

Attributes

This pattern identifies volumes to which the rule applies.

Method

Stamping method to use when generating the volumes to which this rule applies.

Weighted Average

Voxel value is weighted average of attribute value from the overlapping particles; weight depends on the coverage attribute, as well as distance of the particle from the sample location.

Covered Average

Same as Weighted Average, but areas outside of particle influence are attenuated, yielding smooth falloff.

Accumulated

Contributions from all particles are simply summed up.

Stochastic

Voxel value is deduced from a single (pseudorandomly selected) overlapping particle.

See also

Geometry nodes