Houdini 19.5 Nodes LOP nodes

Stage Manager

Provides a convenient interface to reference in many files at once and place them in the scene graph tree.

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Since 17.5


This node references in prims from disk and attaches them to prims in the scene graph tree. This is the same function as the Reference LOP, however this node provides a custom interface to make it easy to reference in many files and interactively place them in the tree.

Referencing in many files at a time is often part of a layout workflow, where you start to build a scene by importing available assets and organizing them into a meaningful hierarchy.

Working in a single layer

Because of the way that USD stages are composed, it is not generally possible to perform arbitrary rearrangement of a scene graph hierarchy. However a single layer can be modified in this way, copying, moving, and deleting primitives.

  • You are always looking at and manipulating a single USD layer, not a composed stage. (This is why the contents of the referenced files do not appear in the stage manager tree. Only primitives that exist in the active layer are represented in the tree and can be manipulated by this node.)

  • You can only freely rearrange prims that you created in this node.

Flattening an input stage

In addition to creating new primitives, the Stage Manager can manipulate pre-existing primitives. But because it only works on a single layer, it must flatten all incoming layers into a single layer before you can edit incoming hierarchy. This can be very destructive to a standard layer structure. Be careful if you decide to feed an input stage into this node.

It’s probably better (or at least, less prone to mess up layers) if you use this node without an input, to build up a layer that references in the files you want with the hierarchy you want, and then Merge the output of this node into the layer stack of your stage.

How to

Stage Manager has a custom Qt-based user interface that takes over the parameter editor when this node is selected. You can switch between the custom interface and the regular parameters by clicking the Show/hide parameters button in the Parameter editor’s toolbar.

The following instructions describe how to use the custom interface.

To...Do this

Create a new Xform prim

  • Click the Add button for the “parent” prim you want the new Xform prim to be under.


  • Right click the “parent” prim and choose New folder.

You can use this create new levels of hierarchy to organize the assets you reference in.

Reference in a file

  • Click the button at the top to show/hide the file browser sub-pane on the right.

  • Set the parent directory of the file browser in the text box at the top of the file browser.

  • Drag a file from the file browser into the scene graph tree on the left.

Delete a prim/reference

  • Right-click the row in the tree and choose Delete


  • Select the row and press ⌦ Del.

Explicitly specify which root prim to reference

Usually a file specifies a “default” prim to reference. If the file doesn’t have a default prim, or if you want to reference a different root prim, find the row that references in the file, and double-click in the “Reference Primitive” column. Type the name of the root prim to reference.


  • You can choose variants on top level referenced primitives, and apply transforms.

  • In some cases, the stage manager can be very useful for performing manipulations on the active layer in a procedural manner using expressions in the actual parameters, rather than using the custom panel interface. For example, Edit Target Layer uses a Stage Manager node to move a primitive known to exist in the active layer to a different location in that layer.

  • You can use a Stage Manager node to rename prims in a USD layer on disk.

    1. Reference in the layer you want to edit.

    2. Wire the output into a Stage Manager node. In the stage manager, use the parameter UI to rename prims in the layer.

    3. Wire the Stage Manager output into a USD ROP and use it to write out the results.


You can switch between the custom interface and the regular parameters by clicking the “Show/hide parameters” button in the Parameter editor’s toolbar.

Flatten Input Layers

When this is on (the default), Stage Manager will flatten any incoming layers into a single layer so that it can edit the entire scene graph hierarchy. When this is off, the incoming layers are passed through, but are not editable or visible in the custom interface.

New Primitive Type

Specifies the USD Primitive type of any new primitives created by this node. Choices are Xform, Scope, and None. Xform and Scope can both create a valid USD model hierarchy, and the choice between them will depend on your preferred conventions. Choosing None allows the USD primitive type to be defined by the type of the primitive being referenced in from an external file.

Number of Changes

Each edit performed by this node is recorded as an instance of this multi-parm. The node usually these out automatically as you work in the custom interface, but you can also create them manually.

Change Type

There are five different operations that can be performed by this node. Each one acts on a single primitive, but many of them will implicitly affect all descendants of that primitive.

Create Primitive

Creates a new primitive at a particular location. Ancestor primitives will be created automatically if they don’t already exist. Standard edit operations such as setting a transform or choosing variants can be applied in the same operation.

Copy Primitive

Copies a primitive from one location to another. The original primitive is unaffected. Ancestors of the destination location will be created automatically if necessary. Standard edit operations can be applied to the destination primitive in the same operation.

Edit Primitive

Modifies an existing primitive. Any or all of the supported modifications can be applied in a single operation.

Move Primitive

Similar to Copy, but deletes the primitive in the original location. Ancestors of the destination location will be created automatically if necessary. Standard edit operations can be applied to the destination primitive in the same operation.

Delete Primitive

Deletes the primitive at a particular location (along with all its descendants).

Primitive Path

The scene graph path of the USD primitive that will be affected by this operation. Depending on the Change Type, this primitive may or may not need to exist prior to the operation being applied. If an operation requires a primitive to exist, but it isn’t found, a warning appears on the node. Only a single primitive path can be entered in this parameter (patterns are not supported).

Destination Primitive

For the Copy and Move operations, the destination scene graph path.

Reference File

File path to a USD layer on disk which will be added as a reference on the specified USD primitive.

Reference Primitive Path

The name of the root primitive to import. If this is blank, the node uses the file’s default primitive. If the file has no default prim, it uses the first prim with a transform. If that doesn’t work, it takes the first root prim. If the file has no root prim (that is, it’s empty), this node doesn’t reference in the file at all.

Reference as Payload

Reference this file in as a payload.

Set Transform

When this is on, apply a transform to the referenced primitive. This replaces any other transform operations in the referenced primitive’s xformOpOrder attribute. So, this transform effectively replaces any other transform that might have been set on this primitive.

Transform order

The order in which Houdini applies translates, rotates, and scales, and the order in which it applies rotation.


Movement amount along XYZ axes.


Degrees rotation around XYZ axes.


Non-uniform scaling along XYZ axes.

Uniform scale

Scales the object uniformly along all three axes.

Pivot Transform

Pivot translate

Moves the local origin of the object.

Pivot rotate

Rotates the local origin of the object after translation.

Number of Variants

You can choose which variant of the root primitive is selected when the prim is referenced in. Since primitives can have multiple variant sets, this node allows you to make multiple variant choices.

Variant Set

The name of the variant set to choose a variant from.

Variant Name

The name of the variant to select.

LOP nodes

  • Add Variant

    Adds one or more variants to a variant set on a primitive. This node creates the primitive if it doesn’t exist.

  • Additional Render Vars

    Create multiple render vars.

  • Asset Reference

    Reference, Transform, and select variants of a USD Asset.

  • Assign Material

    Assigns a material to one or more USD primitives. You can use also programmatically assign materials using VEX, programmatically override material settings for each assignment, and programmatically assign materials to geometry subsets.

  • Assign Prototypes

    Switch point instances or USD instanceable prims to instance a different prototype.

  • Attribute VOP

    Create/edit USD attribute values using a VOP network.

  • Attribute Wrangle

    Create/edit USD primitive attributes using a VEX snippet.

  • Auto Select LOD

    Automatically selects a level-of-detail variant based on the primitive’s distance from the camera.

  • Background Plate

    Sets up hold-out or matte objects that leave holes in the scene through which the background is visible. These prims still take shadows and contribute to reflections as if they were the background.

  • Bake Skinning

    Bakes animation driven by a UsdSkel into transforms and point positions.

  • Basis Curves

    Creates or edits a basis curves shape primitive.

  • Begin Context Options Block

    This node begins a block of LOP nodes, within which certain context options have certain values.

  • Blend

    Partially applies edits to a layer’s attributes based on a fractional weight.

  • Blend Constraint

    Blends transforms according to a list of weights specified as parameters.

  • Cache

    Caches the results of cooking the network at different times, increasing playback speed.

  • Camera

    Adds a USD camera to the scene.

  • Capsule

    Creates or edits a capsule (tube with hemispherical ends) shape primitive.

  • Collection

    Creates/edits collections using primitive patterns.

  • Component Geometry

    Geometry container or import source, in a network created by the Component Builder tool.

  • Component Geometry Variants

    Sets up geometry variants, in a network created by the Component Builder tool.

  • Component Material

    Assigns materials to geometry in a network created by the Component Builder tool.

  • Component Output

    Assembles the final Component prim, in a network created by the Component Builder tool.

  • Cone

    Creates or edits a cone shape primitive.

  • Configure Layer

    Edits metadata on a layer.

  • Configure Primitives

    Edits various metadata on one or more primitives.

  • Configure Properties

    Configures metadata on properties (relationships and attributes).

  • Configure Stage

    Configures metadata for how to load layers into the stage and asset resolution.

  • Coordinate System

    Define named coordinate systems used in shaders.

  • Copy Property

    Copy properties from one primitive to another, or renames properties on a primitive.

  • Create LOD

    Uses the PolyReduce SOP to automatically generate multiple levels of detail from a high-res model, and stores them as USD variants.

  • Cube

    Creates or edits a cube shape primitive.

  • Cylinder

    Creates or edits a cylinder shape primitive.

  • Distant Light

    Creates or edits a USD Distant Light, representing a far-off light source such as the sun. Adds some useful Karma-specific attributes.

  • Dome Light

    Creates or edits a USD Dome Light prim. A dome light emits light inward, simulating light coming from the sky/environment surrounding the scene.

  • Drop

    Runs a simulation to drop primitives under gravity.

  • Duplicate

    Creates copies of a prim (and its descendants).

  • Edit

    Interactively transforms prims in the viewer. Can use physics collisions to position props realistically.

  • Edit Context Options

  • Edit Material

    Allows you to edit an existing USD material by modifying parameters and shader connections. This can be useful if the existing material is on a non-editable layer.

  • Edit Material Properties

    Lets you build a spare parameter interface that reflects material or shader input attributes to directly edit their values.

  • Edit Properties

    Lets you build a spare parameter interface to directly edit attribute and relationship values.

  • Edit Properties

    Lets you refer to the parameter on another node to directly edit attribute and relationship values.

  • Edit Prototypes

    Modify the prototypes of native or point instances in-place, without disturbing the instancing setup.

  • Edit Target Layer

    Allows you to apply edits directly in a lower layer, instead of overriding prims and attributes in the active layer.

  • Error

    Generates a message, warning, or error, which can show up on a parent asset.

  • Explore Variants

    Visualize, set, or extract variants on primitives.

  • Extract Instances

    Converts (heroes) an instance into a real editable prim.

  • Fetch

    Grabs the output of another LOP, potentially in another LOP network.

  • File Cache

    Caches (writes out once and then reads from) USD layers (possibly animated) to disk.

  • Follow Path Constraint

    Constrains a prim to follow a path curve.

  • For Each

    The end node of a For-Each loop block.

  • Geometry Sequence

    Imports a sequence of geometry files into LOPs as animated geometry.

  • Geometry Subset VOP

    Creates USD geometry subsets within geometry prims (similar to groups in SOPs) based on evaluating a VEXpression or VOP network.

  • Graft Branches

    Takes prims/branches from the second input and attaches them onto branches of the scene graph tree in the first input.

  • Graft Stages

    Takes scene graph trees from other inputs and attaches them onto branches of the scene graph tree in the first input.

  • HDA Dynamic Payload

    Cooks a OBJ or SOP asset on disk and imports the animated geometry output as a USD payload.

  • Hermite Curves

    Creates or edits a hermite curves shape primitive.

  • Houdini Preview Procedurals

    Summary goes here.

  • Houdini Procedural: Hair

    Houdini Hair Procedural for Solaris.

  • Inline USD

    Parses usda code representing a layer and adds it to the layer stack.

  • Insertion Point

    Represents a point in the node graph where nodes can be inserted.

  • Instancer

    Instances or copies primitives onto points.

  • Instancer

    Create multiple render products sharing common settings.

  • Isolate Scene

    Work in masked areas of the stage.

  • Karma

    Renders the USD scene using Houdini’s Karma renderer.

  • Karma Cryptomatte

    Setup Cryptomatte AOVs for Karma.

  • Karma Fog Box

    Creates a constant volume within a box.

  • Karma Ocean

    Render an ocean with the Karma CPU renderer.

  • Karma Render Properties

    Configure Render Properties for Karma.

  • Karma Standard Render Vars

    Create standard karma render vars (AOVs/Image Planes).

  • LOP nodes

    LOP nodes generate USD describing characters, props, lighting, and rendering.

  • LPE Tag

    Manage Lights LPE Tags.

  • Labs RizomUV Optimize

  • Labs RizomUV Rectangularize

  • Labs RizomUV Unwrap

  • Layer Break

    Starts a new active sublayer that subsequent nodes will edit, and indicates all previous layers will be discarded when saving to disk.

  • Layer Replace

    Replaces all uses of a certain layer with a substitute layer from its second input.

  • Layout

    Provides tools for populating a scene with instanced USD assets. You can place individual components, paint/scatter components in different ways using customizable brushes, and edit existing instances.

  • Light

    Creates or edits a USD Light prim. This node also adds some useful Karma-specific attributes.

  • Light Filter Library

    Authors USD light filter primitives from VOP nodes.

  • Light Linker

    Creates USD light link properties based on rules.

  • Light Mixer

    Lets you interactively edit USD properties for multiple lights.

  • Load Layer for Editing

  • Loft Payload Info

    Adds basic information from inside a payload to the primitive that loads the payload.

  • Look At Constraint

    Constrains a prim to always point toward a target.

  • Mask from Bounds

    Sets a primvar based on whether/by how much selected prims are inside a bounding shape.

  • Match Size

    Resizes and recenters the input geometry to match a reference bounding box.

  • Material Library

    Authors USD material primitives from shader VOP nodes.

  • Material Linker

    Creates material assignments based on rules.

  • Material Variation

    Creates attributes/primvars to override material parameters per-prim/instance.

  • Merge LOP

    Merges the layers from incoming stages into a unified layer stack.

  • Mesh

    Creates or edits a mesh shape primitive.

  • Modify Paths

    Modify asset path attribute values.

  • Modify Point Instances

    Modifies point transforms and property values for individual point instances.

  • Motion Blur

    Adds time samples to allow motion blur when rendering.

  • Null

    This node does nothing. It can be useful to insert a Null into a network as a fixed point in the network that you can refer to by name in expressions/scripts.

  • Output

    Represents the output of a subnetwork. Allows you to design a node asset with multiple outputs.

  • Parent Constraint

    Makes a primitive appear to inherit the transform hierarchy of another prim somewhere else in the tree.

  • Points

    Creates or edits a Points shape primitive.

  • Points Constraint

    Position and Orient primitives using point positions from a geometry.

  • Primitive

    Bulk-creates one or more attributes of a certain type.

  • Prune

    Hides or deactivates primitives and point instances.

  • Python Script

    Lets you write Python code in the node to use the USD API to directly manipulate the stage.

  • RBD Destruction

    An example of how to a fracturing simulation in USD, also useful as a canned effect.

  • Reference

    References the contents of a external USD files and/or layers created by other LOP nodes into a branch of the existing scene graph tree. Can also remove or replace existing references.

  • Render Geometry Settings

    Applies renderer-specific geometry settings to geometry in the scene graph.

  • Render Product

    Creates or edits a UsdRenderProduct prim, which represents an output of a renderer (such as a rendered image file or other file-like artifact produced by a renderer), with attributes configuring how to generate the product.

  • Render Settings

    Creates or edits a UsdRenderSettings prim, which holds the general settings for rendering the scene.

  • Render Var

    Specifies a custom variable computed by the renderer and/or shaders, either a shader output or a light path expression (LPE).

  • Resample Transforms

    Generates interpolated transform time samples from existing time samples on USD prims.

  • Restructure Scene Graph

    This node has various operations for editing prim paths, variant sets, and composition arcs.

  • Retime Instances

    Offsets and/or scales the timing of animation on selected instances.

  • SOP Character Import

    Imports a character or animation from a SOP network into the USD scene graph.

  • SOP Create

    Lets you create geometry in a SOP subnetwork inside this node, so you can create geometry in-place in the LOP network instead of needing a separate SOP network.

  • SOP Crowd Import

    Imports a crowd from a SOP network into the USD scene graph.

  • SOP Import

    Imports geometry from a SOP network into the USD scene graph.

  • SOP Modify

    Converts USD geometry into SOP geometry, runs the SOP subnet inside this node on the geometry, and converts the changes back to USD overrides.

  • Scene Import

    Imports models, materials, and lights from the Object level into the LOP network.

  • Scope

    Creates a scope primitive. Scope is the simplest form of grouping, and does not have a transform. Scopes can be useful for organizing the scene tree.

  • Set Extents

    Sets the bounding box metadata of selected primitives.

  • Set Variant

    Selects (switches to) one of the variants stored in a variant set on a primitive.

  • Simulation Proxy

    Generates low-poly collison geometry suitable for physical simulation and creates a proxy relationship to the original model.

  • Sphere

    Creates or edits a sphere shape primitive.

  • Split Point Instancers

    Splits a point instancer into two or more instances, which divide up the original instances.

  • Split Primitive

    Splits USD geometry prims into child primitives based on geometry subsets or primvar values.

  • Split Scene

    This node splits a scene graph into two disjoint sets of primitives.

  • Stage Manager

    Provides a convenient interface to reference in many files at once and place them in the scene graph tree.

  • Store Parameter Values

    Lets you store temporary (unsaved) data in the stage.

  • Sublayer

    Imports from USD files or other LOP node chains into as sublayers, or removes/replaces/reorders existing sublayers.

  • Subnet

    Encapsulates a LOP subnetwork, allowing you to organize and hide parts of the network.

  • Surface Constraint

    Constrain a prim to stick to a surface.

  • Switch

    Passes through one of several inputs, based on a parameter choice or expression.

  • TimeShift

    Outputs the stage as it is at a different point in the timeline.

  • Transform

    Edits the transforms of selected USD primitives.

  • Transform UV

    Moves, rotates, and scales texture coordinates on USD primitives.


  • USD Render ROP

  • Unassign Material

    Unbinds a material from one or more USD primitives.

  • Value Clip

  • Vary Material Assignment

    Assign different materials across a number of prims to create variation.

  • Volume

    References volume data on disk into a volume prim containing field prims.

  • Xform

    Creates or edits an Xform prim. Xform (and its sub-classes) represents a transform in the scene tree.