Houdini 20.0 Nodes LOP nodes


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

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Since 17.0


This node represents the most basic way to add USD files to your scene. Sublayers tell USD to add the content primitives your scene as-is, without any sort of parenting of the primitives. This node is able to sublayer from multiple files and multiple nodes.

See the section Sublayers Explained for details about this USD concept.


  • You can use the Scene graph layers pane to view the results of adding the sublayers.

  • This node supports sublayering multiple files at once. The

How to

The “target” layer you want to add to the layer stack is often in an external file, however this node can also import the layer(s) in the output of another LOP node.

To...Do this

Sublayer in an external file

  1. Set Sublayer type to “Sublayer files”.

  2. Set File to the file path of the layer file you want to load in.

Sublayer in a layer the output of a LOP node

  1. Set Sublayer type to “Sublayer inputs”.

  2. Connect the LOP with the layers you want to this node’s multi-input.

    When you wire more than one node into the multi-input, the ordering is weaker to stronger, from left to right. (That is, opinions in layers closer to the left side of the multi-input are weaker than opinions in layers closer to the right side.)


You can use the table below the parameters in the parameter editor to re-order the connections to the multi-input.

Remove an existing sublayer file from the stack


This only works for layers with Save Path metadata (that is, layers loaded from disk, or layers you've explicitly set Save Path metadata on with the Configure Layer LOP).

  1. Set Find sublayers to the file path in the layer’s source file path metadata (or a pattern matching the source file path).


    In Houdini 18.0, the node only matches against each layer’s “source file” metadata (the path of the file the layer was loaded from). So this only matches layers that exist on disk. Even if a layer has Save Path metadata, until the layer is actually saved to disk, it will not have a source path you can match against.

    (A future version of Houdini will likely fix this to match against Save Path metadata as well.)

  2. Turn on Remove found sublayers.


First Input

The stage to which this node will add new sublayers.

Second Input (multi-input)

When Sublayer Type is “Sublayer Inputs”, the node adds layers from stages connected to this multi-input into the layer stack in the first input.


Load Payloads

When this option is on (the default), the payload loading configuration of the input stage is not changed. When this option is off, the stage’s load mask will be modified to turn off all payload loading. Note that this will affect the loading of payloads anywhere in the stage, not just payloads loaded by the sublayers added by this node. Use the Configure Stage LOP to have more control over which payloads are loaded on the stage.

Copy Layer Metadata to Stage Root Layer

Layer metadata is not composed by USD following the normal rules. In order for values like the frames per second or up axis settings to apply to a USD stage, they must be set directly on the root layer of the stage. This means any layer metadata authored on a file being loaded by this node will not affect the stage level metadata. This options allow for the explicit copying of layer metadata from the first layer loaded by this node on to the stage’s root layer. If multiple files are specified, it it always the first file that has its values copied to the root layer.

The Auto option for this parameter acts like a Yes (copy the sublayer’s metadata to the root layer) if there is no input connected to the first input of this node. Otherwise it behaves as a No (does not affect the stage’s root layer metadata).

Edit Root Layer

When this is on (the default), the new sublayers are added to the layer stack. This is usually what you want. When this is off, the content of the imported layers become sublayers of the active layer.

Turning this on or off usually does not make a visible difference, but affects the priority given to opinions on the layers, and what content is in what layers when you write USD to disk.

Find Sublayers

A space-separated list of patterns that match layers by their “source file” metadata. This selects the layers for removal or reordering when you use the Remove found sublayers or Sublayer position parameters below.

Remove Found Sublayers

Turn this on to remove any layers that match the patterns the Find sublayers.

This is useful if you want to replace layers rather than just add them. For example, you may be editing a layer that has sublayers for animation, effects, and lighting. If your LOP network generates a new version of the effects layer, you would want to remove the existing effects layer and replace it with the new one.

Sublayer Type

Where to add sublayers from.

Sublayer Files and Inputs

Import layers from file(s) on disk, and then import layers from LOP node branches connected to this node’s multi-input.

Sublayer Files

Import layers from file(s) on disk.

Sublayer Inputs

Import layers from LOP node branches connected to this node’s multi-input.

Handle Missing Files

When Sublayer type is “Sublayer files”, what to do when a file (either a file you specify or a file referenced inside another file) cannot be found.

Error for Missing Files: The node errors, preventing cooking the rest of the network.

Warn for Missing Files

The node shows a warning, then passes through the first input unchanged.

Ignore Missing Files

The node silently ignores the missing file, and passes through the first input unchanged.

Allow Missing Files on the Stage

Author the reference to the sublayer even if it currently doesn’t exist. This node and the following nodes will probably print warnings from the USD libraries about missing files.

Sublayer Position

Where in the sublayer stack to insert the new layers. The position affects the priority of its opinions compared to other layers.

Strongest Position

Add the new layers as the strongest sublayers. The opinions in these layers override all other layers.

Weakest Position

Add the new layers as the weakest sublayers. The opinions in these layers will be overridden by any sublayer with an opinion on the same data.

Strongest File Layer’s Position

Add the new layers where their opinions are stronger than the strongest layer that is loaded from a file on disk. This option can be used to keep all LOP-authored layers together, allowing them to be flattened into a single layer when saving to disk.

Strongest Found Layer’s Position

Add the new layers where their opinions are stronger than the strongest layer found by the Find Layers parameter.

Weakest Found Layer’s Position

Add the new layers where their opinions are weaker than the weakest layer found by the Find Layers parameter.

Specific Index

Insert the new layers into the sublayer stack at a specific position (set by the Position index parameter below). Lower numbers represent stronger opinions. Setting this to 0 is the same as choosing “Strongest Position”.

Position Index

When Sublayer position is “Specific index”. Insert the new layers at this specific position. Lower numbers represent stronger opinions. Setting this to 0 is the same as setting Sublayer position to “Strongest Position”.

Number of Files

This node can sublayer in more than one file at a time. Enter the number of files to import, or click the plus and minus buttons to add or remove layer files.


Whether to load this file.


The file path to the file.

Mute Layer

Load the layer but immediately mute it. This may be useful if the layer must be loaded for other layers to work, but you don’t need to edit or display it.

Reload Files

Click to reload the contents of all files imported by this node.

Enable Inputs

Whether to add the LOP node layers connected to the multi-input to the stage.


SeparatedAnimation Example for Sublayer

This example demonstrates the use of usd rops to output geometry and animation and the use of a sublayer lop to import them.

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 From Node

    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 Clip Sequence

  • 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 Feather Procedural

    Generates feathers for rendering.

  • Houdini Preview Procedurals

    Invokes Houdini Procedurals while working interactively.

  • Houdini Procedural: Hair

    Houdini Hair Procedural for Solaris.

  • Houdini Procedural: Ocean

    Houdini Ocean 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 Physical Sky

    Creates a Karma Sky Dome and Sun Light rig.

  • Karma Render Properties

    Configure Render Properties for Karma.

  • Karma Sky Dome Light

    Creates or edits a Karma Sky Dome Light.

  • Karma Standard Render Vars

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

  • LPE Tag

    Manage Lights' LPE Tags.

  • Labs Karma AOVs for RenderMan Denoiser

    Generates AOVs for the Pixar RerderMan denoiser.

  • 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.

  • Merge Point Instancers

    Merges point instancers into a single consolidated point instancer.

  • 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 for 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 Doctor

    Validates primitives on a USD stage.

  • 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.