Volumes & VDB#

VDB creation, active regions, level sets, fields and the rest of the Volume SOPs (pcg106).

68 nodes.

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Contents#

• Convert VDB (PCG) — Converts between VDBs, dense volumes, polygons, fog and SDF.
• VDB (PCG) — Creates an empty or filled VDB volume of a given class, type and voxel size.
• VDB Activate (PCG) — Changes which voxels of a VDB are active, by box, voxel range, dilation, reference geometry or value.
• VDB Activate SDF (PCG) — Activates a narrow band of a given width around the surface of an SDF, with true distances.
• VDB Advect (PCG) — Moves volume content through a velocity field.
• VDB Advect Points (PCG) — Moves points through a velocity field or onto a closest-point field.
• VDB Analysis (PCG) — Computes gradient, curvature, Laplacian, closest point, divergence, curl, length or normalized fields.
• VDB Clip (PCG) — Deactivates the voxels of a VDB outside (or inside) a box, a mask VDB or a camera frustum.
• VDB Combine (PCG) — Combines pairs of volumes with arithmetic, SDF boolean or activity operations.
• VDB Densify (PCG) — Makes every voxel of a VDB active.
• VDB Diagnostics (PCG) — Checks VDBs for invalid values, wrong backgrounds and bad SDF gradients, and optionally repairs them.
• VDB Extrapolate (PCG) — Widens an SDF band, converts fog to SDF, or extends fields off a surface.
• VDB Fill (PCG) — Sets a box of voxels to a value and activates or deactivates it.
• VDB Fracture (PCG) — Cuts SDF volumes into fragments with cutter shapes.
• VDB from Particle Fluid (PCG) — Builds a smooth fluid surface SDF from particles.
• VDB from Particles (PCG) — Builds an SDF from points as spheres of their pscale.
• VDB from Polygons (PCG) — Builds an SDF (and optionally fog and attribute volumes) from a polygon mesh.
• VDB LOD (PCG) — Builds lower-resolution levels of detail of volumes.
• VDB Merge (PCG) — Merges VDBs with the same name (or all of them) into one.
• VDB Metadata (PCG) — Sets the name, class, background and VDB flag of volumes.
• VDB Morph SDF (PCG) — Moves one SDF surface towards another over time.
• VDB Noise (PCG) — Adds fractal noise to the surface of an SDF.
• VDB Occlusion Mask (PCG) — Marks the voxels hidden from a camera behind a surface.
• VDB Platonic (PCG) — Creates the SDF or fog of a sphere or a Platonic solid.
• VDB Points Group (PCG) — Groups points by percentage, bounding box or SDF range.
• VDB Potential Flow (PCG) — Computes the potential flow of a fluid around the solid of an SDF.
• VDB Project Non-Divergent (PCG) — Removes the divergence from a velocity field (pressure projection).
• VDB Prune (PCG) — Collapses constant regions of a VDB and deactivates background regions.
• VDB Ray (PCG) — Projects points onto the surface of a volume, along their normals or to the closest point.
• VDB Rebuild SDF (PCG) — Builds a clean SDF from an iso contour of any scalar volume.
• VDB Remap (PCG) — Remaps volume values from one range to another through a ramp.
• VDB Renormalize SDF (PCG) — Restores the distance property of an SDF after it was edited.
• VDB Resample (PCG) — Resamples volumes to a new voxel size or to match a reference VDB.
• VDB Scatter (PCG) — Scatters points in the active voxels of volumes.
• VDB Segment by Connectivity (PCG) — Splits volumes into their connected pieces.
• VDB Smooth (PCG) — Smooths volumes with a mean, Gaussian or median filter, or offsets them.
• VDB to Spheres (PCG) — Fills the inside of an SDF with non-overlapping spheres (points with pscale).
• VDB Topology to SDF (PCG) — Turns the active region of a VDB into an SDF.
• VDB Transform (PCG) — Translates, scales and rotates volumes.
• VDB Vector Merge (PCG) — Merges three scalar volumes into one vector volume.
• VDB Vector Split (PCG) — Splits vector volumes into scalar .x / .y / .z volumes.
• VDB Visualize Tree (PCG) — Draws the leaf / internal node layout and the active voxels of VDBs as geometry.
• Volume Adjust Fog (PCG) — Adjusts fog density with patterns, ramps and pre / post processing.
• Volume Bound (PCG) — Builds the bounding box of the voxels that meet a condition.
• Volume Break (PCG) — Cuts polygons with the surface of an SDF.
• Volume Compress (PCG) — Quantizes and simplifies volume values the way compressed volumes store them.
• Volume Convolve 3×3×3 (PCG) — Convolves volumes with a 3×3×3 kernel.
• Volume Feather (PCG) — Limits how fast volume values change, growing or shrinking fog smoothly.
• Volume FFT (PCG) — Computes the forward or inverse Fourier transform of volumes.
• Volume from Attrib (PCG) — Writes a point attribute into volumes.
• Volume Merge (PCG) — Flattens several volumes into one base volume.
• Volume Optical Flow (PCG) — Estimates the displacement field between two volumes.
• Volume Patch (PCG) — Fills a masked region of a volume seamlessly from another volume.
• Volume Ramp (PCG) — Remaps volume values through a scalar or color ramp.
• Volume Rasterize Curve (PCG) — Turns curves into density, color or SDF volumes.
• Volume Rasterize Particles (PCG) — Splats points into volumes with filter kernels.
• Volume Rasterize Points (PCG) — Turns points into soft spheres of density in volumes.
• Volume Reduce (PCG) — Reduces each volume to one number (maximum, average, sum, ...).
• Volume Resize (PCG) — Changes the bounds of volumes without resampling.
• Volume SDF (PCG) — Converts any volume into an SDF of one of its iso contours.
• Volume Slice (PCG) — Cuts a plane through volumes as a mesh, points or a thin volume.
• Volume Splice (PCG) — Joins volumes of the same name into one larger volume.
• Volume Stamp (PCG) — Copies volumes onto points and composites them into a destination.
• Volume Trail (PCG) — Traces streamlines from points through a velocity field.
• Volume Velocity (PCG) — Adds uniform, vortex, curl-noise and point velocities to a velocity volume.
• Volume Velocity from Curves (PCG) — Builds a velocity volume from the tangents of nearby curves.
• Volume Velocity from Surface (PCG) — Builds a velocity field inside a closed surface from a divergence attribute.
• Volume Visualization (PCG) — Sets how the viewport draws volumes: smoke, rainbow, iso surface or invisible.

Nodes#

Convert VDB (PCG)#

PCG_ConvertVDB · category PCG/volume · Houdini: Convert VDB (SOP)

Converts between VDBs, dense volumes, polygons, fog and SDF.

To VDB (from a Houdini volume; Deactivate Tolerance drops background voxels), to Volume (densify, no mask), to Polygons (closed iso-surface at Isovalue; Adaptivity reduces the face count), or between classes: fog -> SDF (Fog Isovalue, ±Half Band voxels) and SDF -> fog (OpenVDB's ramp across the interior band).

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Outputs

Parameters

VDB (PCG)#

PCG_VDB · category PCG/volume · Houdini: VDB (SOP)

Creates an empty or filled VDB volume of a given class, type and voxel size.

Creates a VDB prim covering the reference geometry's bounds (+ Padding) or Size / Center at Voxel Size. Class SDF / Fog / None, scalar or vector. Empty (no active voxels, every voxel = Background) unless Fill Active is on (every voxel active with Value). Background defaults to 0 (fog / none) or 3 voxels (SDF).

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Parameters

VDB Activate (PCG)#

PCG_VDBActivate · category PCG/volume · Houdini: VDB Activate (SOP)

Changes which voxels of a VDB are active, by box, voxel range, dilation, reference geometry or value.

Combines the active region with a region (Union / Intersect / A − B / Copy). Region Type: Position (world box), Voxel (inclusive index box, voxel 0 = the bounding-box minimum), Expand (dilate by voxels or distance; face / face+edge / face+edge+vertex pattern), Reference (second input: bounding box, its VDBs' active voxels, the convex hull of its points, or inside its implicit surface, offset in voxels / world), Deactivate (voxels within Tolerance of the background) and Fill SDF (the inside of an SDF). Union / Copy can write Value.

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Parameters

VDB Activate SDF (PCG)#

PCG_VDBActivateSDF · category PCG/volume · Houdini: VDB Activate SDF (SOP)

Activates a narrow band of a given width around the surface of an SDF, with true distances.

The narrow band |φ| ≤ Half-Width voxels around the surface becomes active and gets true distances (redistanced from the zero crossing); everything else is inactive ±background (the background becomes the band width). The input SDF is assumed to be right near its surface.

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Outputs

Parameters

VDB Advect (PCG)#

PCG_VDBAdvect · category PCG/volume · Houdini: VDB Advect (SOP)

Moves volume content through a velocity field.

Moves the selected grids through a velocity (a vector VDB, or vel.x/.y/.z volumes) in the second input for Timestep: Semi-Lagrangian / Mid-Point / RK3 / RK4 back-tracing, Substeps, limiter (none / clamp to the source neighbourhood extrema / revert to first order). VDB grids grow so the content does not leave them; SDFs (Respect Grid Class) are renormalised.

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Outputs

Parameters

General Advection

VDB Advect Points (PCG)#

PCG_VDBAdvectPoints · category PCG/volume · Houdini: VDB Advect Points (SOP)

Moves points through a velocity field or onto a closest-point field.

Advection (RK1–RK4 through the velocity for Timestep in Substeps), Projection (to a closest-point vector field, VDB Analysis → Closest Point) or Constrained Advection (both); Output Streamlines adds the paths as polylines.

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Outputs

Parameters

VDB Analysis (PCG)#

PCG_VDBAnalysis · category PCG/volume · Houdini: VDB Analysis (SOP), Volume Analysis (SOP)

Computes gradient, curvature, Laplacian, closest point, divergence, curl, length or normalized fields.

Gradient, Curvature (mean curvature ∇·(∇φ/|∇φ|)), Laplacian, Closest Point (P − φ∇φ) on scalar grids; Divergence, Curl, Length, Normalize on vector grids. Central differences in world units. An optional mask VDB (second input) zeroes the result outside its active voxels. Vector results are vector grids (VDB Vector Split for .x / .y / .z).

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Parameters

VDB Clip (PCG)#

PCG_VDBClip · category PCG/volume · Houdini: VDB Clip (SOP)

Deactivates the voxels of a VDB outside (or inside) a box, a mask VDB or a camera frustum.

Keeps the active voxels inside (or outside, Keep Inside off) the clipping region -- the bounding box of the second input, the active voxels of a mask VDB there, or the view frustum of the camera input (frame edges, near and far planes) -- expanded by Padding; the rest become inactive background. For SDFs the removed voxels take the outside background value. The grid is not resampled into a frustum-shaped grid; voxels keep their places.

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Parameters

VDB Combine (PCG)#

PCG_VDBCombine · category PCG/volume · Houdini: VDB Combine (SOP)

Combines pairs of volumes with arithmetic, SDF boolean or activity operations.

A × A Multiplier with B × B Multiplier (B resampled to A's grid; A grows to cover B for VDBs): Copy A / B, Invert A, Add, Subtract, Multiply, Divide, Maximum, Minimum, (1 − A) × B, A + (1 − A) × B, SDF Union / Intersection / Difference, Replace A with Active B, and Activity Union / Intersection / Difference (masks only). Collation: A/B pairs, each A with the first B, or flatten all A into the first A. Deactivate Background Voxels, Prune.

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Outputs

Parameters

VDB Densify (PCG)#

PCG_VDBDensify · category PCG/volume · Houdini: VDB Densify (SOP)

Makes every voxel of a VDB active.

Every voxel becomes active (the VDB keeps its values; inactive ones held the background).

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Outputs

Parameters

VDB Diagnostics (PCG)#

PCG_VDBDiagnostics · category PCG/volume · Houdini: VDB Diagnostics (SOP)

Checks VDBs for invalid values, wrong backgrounds and bad SDF gradients, and optionally repairs them.

Tests: finite values, a valid background, inactive voxels holding the background, SDF gradient magnitude within Tolerance of 1 (in the band), active values within [Min, Max]. Repair: non-finite -> background, inactive -> background, values clamped into the range. Mark: adds "<name>_bad" fog VDBs = 1 at failing voxels. The report lists the counts per volume.

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Outputs

Parameters

Tests

Output

VDB Extrapolate (PCG)#

PCG_VDBExtrapolate · category PCG/volume · Houdini: VDB Extrapolate (SOP)

Widens an SDF band, converts fog to SDF, or extends fields off a surface.

Expand SDF Narrowband (by Dilation voxels, true distances), Convert Fog VDB to SDF, Renormalize SDF, or Extend Field(s) off the surface of the fog / SDF source: each voxel of the Extension Group grids takes the value at its closest voxel on the surface (what fast sweeping converges to).

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VDB Fill (PCG)#

PCG_VDBFill · category PCG/volume · Houdini: VDB Fill (SOP)

Sets a box of voxels to a value and activates or deactivates it.

Sets a box -- inclusive index range, world range, or the reference geometry's bounds -- to Value (x only for scalar grids) and makes it active (or inactive: then it takes the background).

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Outputs

Parameters

VDB Fracture (PCG)#

PCG_VDBFracture · category PCG/volume · Houdini: VDB Fracture (SOP)

Cuts SDF volumes into fragments with cutter shapes.

Cuts each SDF with the cutters of the second input (polygons -> exact SDF on the same grid, or SDF VDBs), optionally instanced on the points of the third input (centred, random rotation): inside piece max(φ, φc), residual max(φ, −φc). Allow Cutter Overlap cuts the earlier fragments too; Separate Cutters by Connectivity uses each connected piece of the cutter separately.

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VDB from Particle Fluid (PCG)#

PCG_VDBFromParticleFluid · category PCG/volume · Houdini: VDB from Particle Fluid (SOP)

Builds a smooth fluid surface SDF from particles.

A smooth fluid surface from particles: spheres of Influence Scale × separation / 2 (isolated droplets: Droplet Scale), voxel size = Particle Separation × Voxel Scale, then Dilate, Smooth passes and Erode (in units of half a separation).

Inputs

Outputs

Parameters

Filtering

VDB from Particles (PCG)#

PCG_VDBFromParticles · category PCG/volume · Houdini: VDB from Particles (SOP)

Builds an SDF from points as spheres of their pscale.

SDF union of spheres of radius pscale × Particle Scale; particles smaller than Minimum Radius (voxels) are ignored; Velocity Trails add tapering spheres back along v × Velocity Scale every Trail Resolution × radius. Optional fog VDB.

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Outputs

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Output

VDB from Polygons (PCG)#

PCG_VDBFromPolygons · category PCG/volume · Houdini: VDB from Polygons (SOP)

Builds an SDF (and optionally fog and attribute volumes) from a polygon mesh.

Exact SDF of the mesh at Voxel Size (or the reference VDB's), narrow band of Exterior / Interior Band voxels (or world units; Fill Interior keeps the whole inside), or an unsigned distance field. Optional fog VDB (0 outside, 0 -> 1 across the interior band) and surface attribute VDBs: for each listed point / vertex / prim attribute, the value at the closest surface point.

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Outputs

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Output

Attribute Transfer

VDB LOD (PCG)#

PCG_VDBLOD · category PCG/volume · Houdini: VDB LOD (SOP)

Builds lower-resolution levels of detail of volumes.

Level L keeps every 2^L-th sample after a 2^L box filter (level 0 = the input). Single Level, Level Range (start, end, step) or an LOD Pyramid of Count levels; outputs are named <name>_level<L> unless Preserve Grid Names (single level).

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VDB Merge (PCG)#

PCG_VDBMerge · category PCG/volume · Houdini: VDB Merge (SOP)

Merges VDBs with the same name (or all of them) into one.

VDBs of the same class collated by name / primitive number / all are merged into one whose grid covers all of them (first one's voxel size): fog add (or none), SDF union / intersect, other add.

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VDB Metadata (PCG)#

PCG_VDBMetadata · category PCG/volume · Houdini: VDB Metadata (SOP)

Sets the name, class, background and VDB flag of volumes.

Sets the name, class, background and VDB flag of the selected volumes (each with a toggle).

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VDB Morph SDF (PCG)#

PCG_VDBMorphSDF · category PCG/volume · Houdini: VDB Morph SDF (SOP)

Moves one SDF surface towards another over time.

Moves the source surface toward the target (second input): ∂φ/∂t + φ_target |∇φ| = 0 (Godunov upwind, CFL-limited substeps) for Timestep, renormalising every Renorm Steps substeps. A large timestep ends at the target. Optional alpha mask (third input) blends.

Inputs

Outputs

Parameters

Alpha Mask

VDB Noise (PCG)#

PCG_VDBNoise · category PCG/volume · Houdini: VDB Noise (SOP)

Adds fractal noise to the surface of an SDF.

φ − Amplitude × fractal Perlin noise (Frequency, Octaves, Lacunarity, Gain, Roughness, Noise Offset); Straight / Absolute / Inverse Absolute. Positive noise pushes the surface out. An optional mask volume (second input) suppresses or scales the noise.

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Mask

VDB Occlusion Mask (PCG)#

PCG_VDBOcclusionMask · category PCG/volume · Houdini: VDB Occlusion Mask (SOP)

Marks the voxels hidden from a camera behind a surface.

A fog VDB "<name>_occlusion" on each SDF's grid: 1 where the voxel is hidden from the camera because the line of sight to the eye passes through the inside first; Erode shrinks it. (Houdini builds the mask in a camera frustum grid; here it lives on the input grid.)

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VDB Platonic (PCG)#

PCG_VDBPlatonic · category PCG/volume · Houdini: VDB Platonic (SOP)

Creates the SDF or fog of a sphere or a Platonic solid.

SDF (narrow band of Half-Band Width voxels) or fog of a sphere or a Platonic solid of the given radius (circumradius for the solids) and centre; exact distances to the solid's faces.

Outputs

Parameters

VDB Points Group (PCG)#

PCG_VDBPointsGroup · category PCG/volume · Houdini: VDB Points Group (SOP)

Groups points by percentage, bounding box or SDF range.

A point group from: a percentage or a count (random, or seeded by an attribute), a bounding box or the bounds of the second input, and an SDF range (the second input's SDF, Min ≤ φ ≤ Max, invertible). Filters combine with AND.

Inputs

Outputs

Parameters

Number

Bounding

SDF

VDB Potential Flow (PCG)#

PCG_VDBPotentialFlow · category PCG/volume · Houdini: VDB Potential Flow (SOP)

Computes the potential flow of a fluid around the solid of an SDF.

Flow around the solid of an SDF in a domain dilated by Dilation Voxels: ∇²φ = 0 with no flow through the solid (Neumann, driven by the Background Velocity) and φ = 0 at the domain border; outputs the velocity ∇φ (+ background when Apply Background Velocity) as a vector VDB, and optionally the potential.

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VDB Project Non-Divergent (PCG)#

PCG_VDBProjectNonDivergent · category PCG/volume · Houdini: VDB Project Non-Divergent (SOP)

Removes the divergence from a velocity field (pressure projection).

Removes the divergence of vector grids: ∇²p = ∇·u (conjugate gradient, Iterations / Tolerance), u − ∇p. Without a collider p = 0 beyond the grid; Bounding Box collider = no flow through the grid border; a VDB collider (second input) = no flow into its inside / active voxels. Output Pressure adds p.

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VDB Prune (PCG)#

PCG_VDBPrune · category PCG/volume · Houdini: VDB Prune (SOP)

Collapses constant regions of a VDB and deactivates background regions.

Value: 8³ leaves whose values differ by at most Tolerance collapse to one constant (their mean). Inactive: leaves within Tolerance of the background are deactivated. Level Set: voxels with |φ| ≥ background are deactivated (outside +background, inside −background).

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Parameters

VDB Ray (PCG)#

PCG_VDBRay · category PCG/volume · Houdini: VDB Ray (SOP)

Projects points onto the surface of a volume, along their normals or to the closest point.

Moves points onto the surface of the VDB in the second input: Ray Intersection along N (or reversed, from Bias; nearest or farthest hit; sphere tracing + bisection) or Closest Surface Point (the exact closest point on the extracted iso surface, at any distance from it). Scale moves only part of the way; Store Distances writes dist; Ray Hit Group collects hits.

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Parameters

VDB Rebuild SDF (PCG)#

PCG_VDBRebuildSDF · category PCG/volume · Houdini: VDB Rebuild SDF (SOP)

Builds a clean SDF from an iso contour of any scalar volume.

An SDF from the Isovalue contour of any scalar grid (fog: dense = inside), with new exterior / interior bands (voxels or world units); Fill Interior keeps the whole inside active.

Inputs

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Parameters

VDB Remap (PCG)#

PCG_VDBRemap · category PCG/volume · Houdini: VDB Remap (SOP)

Remaps volume values from one range to another through a ramp.

Input Range -> Output Range through the Transfer Function ramp (empty = linear). Below / Above the input range: Clamp, Preserve (keep the value) or Extrapolate (continue the end slope). The background is remapped too; Deactivate turns voxels equal to the new background inactive.

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VDB Renormalize SDF (PCG)#

PCG_VDBRenormalizeSDF · category PCG/volume · Houdini: VDB Renormalize SDF (SOP)

Restores the distance property of an SDF after it was edited.

Restores |∇φ| = 1 (exact distance to the zero crossing), keeping the band.

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VDB Resample (PCG)#

PCG_VDBResample · category PCG/volume · Houdini: VDB Resample (SOP)

Resamples volumes to a new voxel size or to match a reference VDB.

Same world content on a new grid: Explicitly (scale the voxel size, translate in voxels, rotate about the pivot -- the grid stays axis aligned), To Match Reference VDB (second input), Using Voxel Size Only, or Using Voxel Scale Only. Nearest / linear interpolation; SDFs are redistanced (Rebuild SDF).

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Outputs

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VDB Scatter (PCG)#

PCG_VDBScatter · category PCG/volume · Houdini: VDB Scatter (SOP)

Scatters points in the active voxels of volumes.

Points in the active voxels: Point Total, Point Density (per unit volume) or Points Per Voxel; Spread jitters within the voxel; Scale Density by Voxel Values (fog / other); SDFs scatter in the Interior, on the Isosurface (projected onto it) or in the Narrow Band. Keep Original Geometry, Scatter Group.

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Outputs

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VDB Segment by Connectivity (PCG)#

PCG_VDBSegment · category PCG/volume · Houdini: VDB Segment by Connectivity (SOP)

Splits volumes into their connected pieces.

Splits each volume into connected pieces: SDF interiors, or active non-background voxels of fog / other grids (face connectivity). Pieces are named <name>_<n> (Append Segment Number) and get a random Cd (Color Segments).

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Outputs

Parameters

VDB Smooth (PCG)#

PCG_VDBSmooth · category PCG/volume · Houdini: VDB Smooth (SOP)

Smooths volumes with a mean, Gaussian or median filter, or offsets them.

Mean / Gaussian / Median over a cube of ± Filter Voxel Radius (or world radius), or Offset, Iterations times; only active voxels change; an optional alpha mask (second input, Min / Max cutoff, invert) blends.

Inputs

Outputs

Parameters

Alpha Mask

VDB to Spheres (PCG)#

PCG_VDBToSpheres · category PCG/volume · Houdini: VDB to Spheres (SOP)

Fills the inside of an SDF with non-overlapping spheres (points with pscale).

Greedy packing inside the Isovalue contour: Point Count random candidates, repeatedly the deepest becomes a sphere; others shrink to stay outside it (or, Overlapping, only those inside it are dropped). Radii in voxels or world units, Min / Max Radius and Min / Max Spheres. Output: points with pscale and id (copy a sphere onto them; sphere primitives are not a prim type here).

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Parameters

VDB Topology to SDF (PCG)#

PCG_VDBTopologyToSDF · category PCG/volume · Houdini: VDB Topology to SDF (SOP)

Turns the active region of a VDB into an SDF.

The active voxels as a solid: an SDF with the surface half a voxel outside the outermost active samples (exact Euclidean distance transforms), after Voxel Dilation and Closing Width (dilate then erode); Smoothing Steps of mean filtering + redistancing. Narrow band of Half-Band voxels (or world units).

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VDB Transform (PCG)#

PCG_VDBTransform · category PCG/volume · Houdini: VDB Transform (SOP)

Translates, scales and rotates volumes.

Translate and (non-uniform) scale move the grid exactly; with a rotation the grid is resampled into the axis-aligned bounds of the rotated one at the same voxel size (grids here are axis aligned). Order: scale, rotate, translate about the pivot. Transform Vectors rotates / scales vector values.

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Parameters

VDB Vector Merge (PCG)#

PCG_VDBVectorMerge · category PCG/volume · Houdini: VDB Vector Merge (SOP), Volume Vector Join (SOP)

Merges three scalar volumes into one vector volume.

Pairs the X / Y / Z scalar grids (by base name for patterns like *.x, else in order) into vector grids on the X grid's samples; missing components are 0. Named after the X grid's base name, or Merged VDB Name (# = number). Remove Source VDBs deletes the scalars.

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VDB Vector Split (PCG)#

PCG_VDBVectorSplit · category PCG/volume · Houdini: VDB Vector Split (SOP), Volume Vector Split (SOP)

Splits vector volumes into scalar .x / .y / .z volumes.

Each vector grid becomes scalar grids <name>.x / .y / .z; scalar grids pass through. Keep Source Volumes keeps the vector grids too.

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Outputs

Parameters

VDB Visualize Tree (PCG)#

PCG_VDBVisualizeTree · category PCG/volume · Houdini: VDB Visualize Tree (SOP)

Draws the leaf / internal node layout and the active voxels of VDBs as geometry.

Leaf nodes (8³ blocks holding active voxels) and internal nodes (128³ blocks) as wireframe boxes or points, active voxels as boxes or points, the grid bounding box; groups leaves / internal / voxels / bbox and Cd. Keep Original Geometry keeps the volumes.

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Outputs

Parameters

Volume Adjust Fog (PCG)#

PCG_VolumeAdjustFog · category PCG/volume · Houdini: Volume Adjust Fog (SOP)

Adjusts fog density with patterns, ramps and pre / post processing.

Pre-process (overwrite with Initial Value, complement), an adjustment of Adjust Value × pattern (constant / random / noise / line / radial / bounding box, through the Remap Ramp, scaled to Range) combined by Operation, post-process (scale, add, clamp, complement), blended by Blend Amount or a blend volume.

Inputs

Outputs

Parameters

Pre-Process

Post-Process

Blend

Volume Bound (PCG)#

PCG_VolumeBound · category PCG/volume · Houdini: Volume Bound (SOP)

Builds the bounding box of the voxels that meet a condition.

A box around the voxels meeting the condition (≥ / > / ≤ / < / = Bounding Value), on the voxel edges (±½ voxel) and expanded by Voxel Padding (−0.5 = bound on voxel centres). No matching voxel: no box.

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Outputs

Parameters

Volume Break (PCG)#

PCG_VolumeBreak · category PCG/volume · Houdini: Volume Break (SOP)

Cuts polygons with the surface of an SDF.

Cuts polygons with the zero surface of the SDF in the second input (fog: its 0.5 contour), linear along edges; keeps inside, outside or both, with inside / outside primitive groups. Snapping Tolerance snaps near-zero point distances to the surface. Holes are not closed.

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Volume Compress (PCG)#

PCG_VolumeCompress · category PCG/volume · Houdini: Volume Compress (SOP)

Quantizes and simplifies volume values the way compressed volumes store them.

16³ tiles whose values differ by at most Constant Tolerance become constant; values are quantised to Quantization Tolerance (ordered dithering optional); Use 16bit Float rounds to half floats; a mask (second input, strictly above Mask Minimum / below Mask Maximum, invertible) zeroes the rest. Values are what a compressed Houdini volume would read back.

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Mask

Volume Convolve 3×3×3 (PCG)#

PCG_VolumeConvolve · category PCG/volume · Houdini: Volume Convolve 3×3×3 (SOP)

Convolves volumes with a 3×3×3 kernel.

27 coefficients (three z planes z−1 / z / z+1, each 3 rows y−1..y+1 of x−1..x+1, whitespace separated); Normalize Kernel divides by their sum; Add, or Add Absolute (|coefficient × voxel|).

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Volume Feather (PCG)#

PCG_VolumeFeather · category PCG/volume · Houdini: Volume Feather (SOP)

Limits how fast volume values change, growing or shrinking fog smoothly.

Caps how fast values may change: High to Low v = max(v, w − rate·d) (fog grows), otherwise min(v, w + rate·d) (fog shrinks), over the 26 neighbours until stable. The rate comes from the Feather Mode (change per distance / per voxel, distance or voxels for a unit change, slope angle).

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Volume FFT (PCG)#

PCG_VolumeFFT · category PCG/volume · Houdini: Volume FFT (SOP)

Computes the forward or inverse Fourier transform of volumes.

Volumes in (real, imaginary) pairs; a lone real volume gets a zero imaginary part (written to a new <name>_imag volume). Invert computes the inverse; Normalize makes forward then inverse the identity; Center DC shifts zero frequency to the centre; Compute 2D Slices transforms each slice along the axis.

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Volume from Attrib (PCG)#

PCG_VolumeFromAttrib · category PCG/volume · Houdini: Volume from Attrib (SOP)

Writes a point attribute into volumes.

Writes a point attribute (second input) into the volumes: Accumulated (trilinear splat, normalised where the total weight exceeds Threshold; Bandwidth widens the splat), or Extrapolated (nearest point within Max Extrapolation Distance / cells). Combined with the volume by Calculation with pre / post add and multiply.

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Calculation

Volume Merge (PCG)#

PCG_VolumeMerge · category PCG/volume · Houdini: Volume Merge (SOP)

Flattens several volumes into one base volume.

Flattens the Merge Group volumes (second input, or the first input's other volumes) into the base volume: Copy (the last), Add, Multiply, Maximum, Minimum, Average; Dest / Source pre add-multiply, post add-multiply, clamps. Clamp at Volume Boundary: B contributes 0 outside its own box.

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Adjustments

Volume Optical Flow (PCG)#

PCG_VolumeOpticalFlow · category PCG/volume · Houdini: Volume Optical Flow (SOP)

Estimates the displacement field between two volumes.

The displacement from each source voxel to the matching goal values (Horn–Schunck with warping, coarse to fine over Pyramid Levels scaled by Pyramid Scale, Iterations per level, displacement blurred by Blurring Window Radius, box or Gaussian; Approximation Window Radius pre-smooths the images). Outputs <source>.x / .y / .z in world units.

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Volume Patch (PCG)#

PCG_VolumePatch · category PCG/volume · Houdini: Volume Patch (SOP)

Fills a masked region of a volume seamlessly from another volume.

Fills the masked region (Mask ≥ Cutoff) of the background with the foreground's features while matching the background on the region's border (Poisson: ∇²u = ∇²foreground inside, u = background outside). Use Foreground as Laplacian: the foreground already is the Laplacian.

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Volume Ramp (PCG)#

PCG_VolumeRamp · category PCG/volume · Houdini: Volume Ramp (SOP)

Remaps volume values through a scalar or color ramp.

Remaps the volumes: Source Min / Max -> 0..1 (clamped) -> the scalar ramp -> Dest Min / Max, or through a colour ramp into three volumes <name>.x / .y / .z (New Name "Cd" gives Cd.x / .y / .z).

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Volume Rasterize Curve (PCG)#

PCG_VolumeRasterizeCurve · category PCG/volume · Houdini: Volume Rasterize Curve (SOP), Volume Rasterize Hair (SOP)

Turns curves into density, color or SDF volumes.

Curves as tubes of radius width / 2 × stroke_pressure (pscale when width is missing): Mask = density (smooth from 1 on the axis to 0 at the tube surface), Color = density + a vector Cd volume, SDF = union of the tubes. Fade lowers the density along the stroke, Flow Rate scales it.

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Volume Rasterize Particles (PCG)#

PCG_VolumeRasterizeParticles · category PCG/volume · Houdini: Volume Rasterize Particles (SOP)

Splats points into volumes with filter kernels.

Each point adds kernel(|x − p| / r) × coverage to density (Gaussian / Box / Cubic Spline), r = max(pscale × Particle Scale, Minimum Filter Size voxels); listed attributes become coverage-weighted averages. Into the first input's volumes when given (same names), else a new grid at Voxel Size.

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Volume Rasterize Points (PCG)#

PCG_VolumeRasterizePoints · category PCG/volume · Houdini: VDB Rasterize Points (SOP), Volume Rasterize (SOP), Volume Rasterize Points (SOP)

Turns points into soft spheres of density in volumes.

Points as spheres of pscale + Exterior Pad: density 1 inside Solid Ratio × r, falling to 0 at r (linear or smooth), × Density Scale × point density; Merge Method maximum / add; optional noise; listed attributes into same-named volumes. Into the first input's volumes or a new grid.

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Noise

Volume Reduce (PCG)#

PCG_VolumeReduce · category PCG/volume · Houdini: Volume Reduce (SOP)

Reduces each volume to one number (maximum, average, sum, ...).

One number per volume (maximum, minimum, average, sum, median at Percentile, RMS, sums and extremes of absolutes, sum of squares; active voxels only for VDBs), optionally × voxel length / area / volume; stored as a detail attribute, a prim attribute, or the volume itself becomes constant.

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Volume Resize (PCG)#

PCG_VolumeResize · category PCG/volume · Houdini: Volume Resize (SOP)

Changes the bounds of volumes without resampling.

New bounds on the same voxel lattice (no filtering): the second input's bounds or Size / Center, Replace / Intersect / Union with the current box, Voxel Padding; new voxels repeat the edge (streak). Keep Data off: an empty volume. Limit Resolution caps each axis.

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Volume SDF (PCG)#

PCG_VolumeSDF · category PCG/volume · Houdini: Volume SDF (SOP)

Converts any volume into an SDF of one of its iso contours.

Any volume -> SDF of its Iso Surface contour (same resolution). Invert flips the sign (use it for fog so dense = inside). Use Maximum Distance clamps to ±Maximum Distance. Distances are exact to the extracted contour (Houdini uses fast marching).

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Volume Slice (PCG)#

PCG_VolumeSlice · category PCG/volume · Houdini: Volume Slice (SOP)

Cuts a plane through volumes as a mesh, points or a thin volume.

A plane through the volumes (XY / YZ / ZX; relative offset −1..1 or a world position + offset; snap to voxels) as a mesh or points with the volumes' values in one attribute (one component per volume), or as thin volumes. Visualize writes Cd through a ramp over the Visualization Range (several volumes -> RGB).

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Visualization

Volume Splice (PCG)#

PCG_VolumeSplice · category PCG/volume · Houdini: Volume Splice (SOP)

Joins volumes of the same name into one larger volume.

Same-named volumes on the same voxel lattice are joined into one volume covering them all; where they overlap the voxel comes from the volume whose centre is nearest. Delete Original Volumes.

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Volume Stamp (PCG)#

PCG_VolumeStamp · category PCG/volume · Houdini: Volume Stamp (SOP)

Copies volumes onto points and composites them into a destination.

The volumes of the third input (matched to the destination by name) are placed on every point of the second input (translated to P, scaled by pscale, rotated by orient) and merged into the destination (maximum / add / minimum / copy / average).

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Volume Trail (PCG)#

PCG_VolumeTrail · category PCG/volume · Houdini: Volume Trail (SOP)

Traces streamlines from points through a velocity field.

A polyline per point through the velocity of the second input (a vector volume or vel.x / .y / .z), RK2: Trail Length in seconds (time) or path length (distance), × traillen; a fixed Number of Steps or CFL-limited steps (CFL × voxel size, at most Max Steps). Visualize: Cd from the speed (Detect Range).

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