liminfoUSD Format Reference
Free reference guide: USD Format Reference
About USD Format Reference
The USD Reference is a comprehensive, searchable guide to Pixar's Universal Scene Description format, covering Stage/Layer configuration, Prim/Property definitions, LIVRPS composition arcs, schema types like UsdGeomMesh and UsdShadeMaterial, and the full Python API including UsdStage, UsdGeom, and UsdShade modules.
This reference organizes USD concepts into five clear categories: Stage/Layer fundamentals (headers, sublayers, defaultPrim, metersPerUnit), Prim/Property operations (def, over, class, attributes, relationships, variantSets), Composition arcs in LIVRPS strength order (Local, Inherits, VariantSets, References, Payload, Specializes), Schema types (Mesh, Xform, Material, Light, Camera, Skeleton), and Python API utilities including usdview and command-line tools like usdcat and usddiff.
Whether you are building a 3D asset pipeline, setting up scene composition in Houdini or Maya, or scripting USD stages with Python, this reference provides instant lookup for every syntax pattern. All content runs locally in your browser with no server processing, and the interface supports both dark and light modes across all devices.
Key Features
- Complete LIVRPS composition arc reference with strength-order explanations and practical examples
- Stage/Layer configuration covering headers, sublayers, defaultPrim, metersPerUnit, and timeCodesPerSecond
- Prim definition patterns including def, over, class, attributes, relationships, and variantSets with customData
- Schema type reference for UsdGeomMesh, UsdGeomXform, UsdShadeMaterial, UsdLuxDomeLight, UsdGeomCamera, and UsdSkelSkeleton
- Python API examples for UsdStage.Open, UsdGeom, and UsdShade with real-world usage patterns
- Command-line tool documentation for usdview, usdcat, and usddiff with key shortcuts
- Category-based filtering across Stage/Layer, Prim/Property, Composition, Schema, and Python API sections
- Bilingual support with full Korean and English reference entries for every USD concept
Frequently Asked Questions
What USD concepts does this reference cover?
This reference covers five core areas: Stage/Layer fundamentals (file headers, sublayers, defaultPrim), Prim/Property definitions (def, over, class, attributes, relationships, variantSets), LIVRPS composition arcs (Local, Inherits, VariantSets, References, Payload, Specializes), Schema types (Mesh, Xform, Material, DomeLight, Camera, Skeleton), and the Python API with command-line tools.
What is the LIVRPS composition order in USD?
LIVRPS defines the strength ordering of composition arcs: Local opinions (strongest), Inherits from class prims, VariantSets selections, References to external assets, Payload for deferred loading, and Specializes for fallback defaults (weakest). This reference includes code examples for each arc type.
Does this reference include Python API examples?
Yes, the reference includes Python examples for UsdStage.Open with prim traversal, UsdGeom API for reading and writing geometry attributes, and UsdShade API for programmatically creating materials and shaders using the pxr module.
What schema types are covered?
The reference covers UsdGeomMesh (polygon mesh definition with points, normals, and UVs), UsdGeomXform (translate/rotate/scale operation stacks), UsdShadeMaterial (shader connections and binding), UsdLuxDomeLight (environment lighting), UsdGeomCamera (render camera settings), and UsdSkelSkeleton (character rigging hierarchies).
How do I use variantSets in USD?
VariantSets allow you to define multiple variations on a single prim. You declare a variantSet block inside a prim definition with named variants, then select the active variant using the variants metadata. This reference shows complete examples of creating and selecting variants for asset variation workflows.
What is the difference between References and Payload in USD?
Both reference external assets, but Payloads support deferred loading. References (LIVRPS #4) are always loaded with the stage, while Payloads (LIVRPS #5) can be selectively loaded or unloaded via stage.Load() and stage.Unload(), making them ideal for heavy geometry assets in large scenes.
Can I convert between USD ASCII and binary formats?
Yes, the reference documents the usdcat command-line tool which converts between .usda (ASCII) and .usdc (binary) formats. Use "usdcat input.usdc -o output.usda" for binary to ASCII, or reverse for ASCII to binary. The --flatten flag outputs a fully composed stage.
Is this reference useful for Houdini, Maya, or Omniverse users?
Absolutely. USD is the interchange format used by Houdini Solaris, Maya USD plugins, and NVIDIA Omniverse. This reference covers the same syntax and API patterns used across all these applications, making it a practical quick-reference for any USD-based pipeline.