Houdini 18.0 Nodes LOP nodes

Configure Layer

Edits metadata on a layer.

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This node edits metadata the affects how a USD layer functions.

  • Some of the metadata is stored on the layer root prim and is saved with the layer on disk.

  • Some metadata is stored in the /HoudiniLayerInfo prim and controls how the layer is written to disk. This primitive is not saved to any USD output.


  • This node will only author a bit of metadata if the corresponding parameter has its checkbox turned on. If the checkbox for a parameter is off, the node will not change any existing metadata corresponding to that parameter.


Save Path

Where the file will be saved if and when the USD is written to disk (by a USD render node). (This is stored in /HoudiniLayerInfo and is not saved to any USD output.)

This path can be altered by an output processor if you have them configured on the render node. For example, it is common in Houdini to have file paths relative to $HIP, but in USD they should be relative to the root layer file. By default, an output processor on the USD render node does this transformation automatically.

Default Primitive

Sets the default primitive for this layer. If another USD file references this layer, but does not explicitly name a primitive, it is given the default primitive. This sets the default primitive for this layer. It must be a root prim (/prim_name) and it must exist in this layer.


Sets a comment on this layer. This comment has no meaning to USD, but may be used to describe the purpose of the layer, or any other information you may wish to associate with the layer.

Start Time

Sets the start time of the playable range for this layer. (This is not enforced in any way, and the layer may not have any animation. This may be used by Houdini’s viewer and tools such as usdview.)

End Time

Sets the end time of the playable range for this layer. (This is not enforced in any way, and the layer may not have any animation. This may be used by Houdini’s viewer and tools such as usdview.)

Time per Second

Applies a scaling factor to time samples stored in the layer. You can use this to non-destructively speed up or slow down animation in the layer.

Frames per Second

For data specified in relation to frames, how many frames fit in a second. (For example, 24 for film, or 30 for NTSC television.)

Up Axis

Which axis (Y or Z) was treated as "up" when this layer was created. This is not used to transform the layer. It serves as a hint that can help identify the cause of orientation problems when you combine USD layers.

Meters Per Unit

The scale at which the scene was modeled. For example, Houdini scenes are often modeled at meter scale (1.0) for physical accuracy, while Maya modelers often work at centimeter scale (0.1). Like Up axis, Houdini doesn’t act on this information (it can’t automatically scale layers because it can’t know which of all the attributes in the scene represent lengths, distances, movement vectors, and so on). It just serves as a hint to help identify the cause of scaling problems when combining USD layers.

Number of Custom Data

The metadata of the layer contains a dictionary for use by software packages and/or studios to store custom data. You can set or edit multiple custom key-value pairs here. Set the number of items to set/edit, or use the plus and minus buttons to add or remove items.

Custom Data Name

For each item of custom data, the name of the item.

Custom Data Type

For each item of custom data, the data type of the value. The only choices are string and number.

Custom Data Value

For each item of custom data, the value to associate with the name.

(Behind the scenes there are two different parameters (customdatastrvaluen and customdatafloatvaluen) both labeled Custom data value, with the visible one controlled by whether Custom data type is set to "string" or "number". This may be relevant if you are using expressions or scripting these values.)

Flatten Input

Prior to configuring the active layer, you can explicitly combine a series of layers created by earlier nodes in the chain.

Do not flatten

Don’t do anything with other layers.

Flatten input layers

Flatten all layers in the layer stack into a single layer, and then configure the metadata of that layer.

Flatten input stage

Flatten the entire stage. This is a much more destructive operation than layer flattening. It bakes overrides, references, and sublayers into a single monolithic tree. Only do this if for some reason you need to incorporate all stage data into a single output file.

Start New Layer

This node is often used to perform the final configuration of a layer’s metadata before creating a new layer to be modified by following LOP nodes. Turn this on to explicitly start a new in-memory active layer that subsequent nodes will use.

See also

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.

  • 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.

  • 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.

  • Bake Skinning

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

  • 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.

  • 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 a collection using selected prims.

  • 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.

  • 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.

  • 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 Properties

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

  • Edit Prototype

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

  • 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.

  • Extract Instances

    Converts an instance into a "real" editable prim.

  • Fetch

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

  • Follow Path Constraint

    Constrains a prim to follow a path curve.

  • For Each

    The end node of a For-Each loop block.

  • Geometry Subset VOP

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

  • Graft

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

  • Inline USD

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

  • Instancer

    Instances or copies primitives onto points.

  • Karma Procedural

    Sets up render-time instantiation for Karma.

  • Karma Render Properties

    Configure Render Properties for Karma (Beta).

  • Karma Standard Render Vars

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

  • LOP nodes

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

  • Layer Break

    Starts a new active sublayer that subsequent nodes will edit.

  • Layer Replace

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

  • Light

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

  • Light Linker

    Creates USD light link properties based on rules.

  • Light Mixer

    Lets you interactively edit USD properties for multiple lights.

  • Load Layer

  • Look At Constraint

    Constrains a prim to always point toward a target.

  • Material Library

    Imports Material VOP nodes as USD material prims.

  • 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.

  • Modify Point Instances

    Modify point transforms and property values for individual point instances.

  • 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 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.

  • Reference

    References the contents of an external USD file into a branch of the existing scene graph tree, or removes/replaces 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).

  • Retime Instances

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

  • 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 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.

  • 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

  • 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.

  • attribvop