The open standard for 3D content creation and data interchange across industries.
USD Core Specification
Overview
What is the Core Specification?
The USD Core Specification formally defines the data representation, scene construction algorithms, and file formats of Universal Scene Description, establishing the open standard for interoperable 3D content creation and interchange. Ratified by Alliance for OpenUSD member organizations including Pixar, NVIDIA, Adobe, Apple, Autodesk, SideFX, and Trimble, it serves as the canonical foundation upon which all domain-specific specifications are built.
Who is the Core Specification for?
Software developers, tool creators, and standards implementers building USD-compatible applications. The specification enables organizations to build independent, compliant implementations, ensuring complex 3D scenes move between tools with consistent behavior across animation, digital twins, and simulation workflows.
Why is the Core Specification important?
The Core Specification addresses three critical needs for the 3D ecosystem:
- Interoperability: Formally specifies how USD data is structured, composed, and exchanged, enabling consistent behavior across tools and platforms.
- Standardization: A compliance rubric and conformance testing framework provide a clear path for validating implementations.
- Foundation: Establishes the base for domain-specific standards in geometry, materials, and physics.
What’s Inside
- Grammar & Data Types: Defines the foundational scalar, dimensioned, and container types (float, matrix4d, token, arrays, dictionaries, list operations) that all USD scene data is built from.
- Document Data Model: Specifies how scene description is organized into layers, specs (prim, attribute, relationship, variant), paths, and metadata fields, independent of any file format.
- Composition: The normative definition of USD’s LIVERPS strength ordering (Local, Inherits, Variants, Relocates, References, Payloads, Specializes) and how multiple layers combine into a single composed result.
- Stage Population & Value Resolution: How composed layers form a stage of prims and properties, and how the final value of any attribute is determined from time samples, splines, defaults, and fallbacks.
- File Formats: Full specifications for USDA (human-readable text), USDC (high-performance binary/Crate), and USDZ (ZIP-based package), plus the USD format that forwards to USDC and USDA.
- Compliance: A rubric and conformance testing framework covering Composed Stage Population, Value Resolution, and Format Implementations (usda, usdc, usd, usdz).
Resources
Get Involved
Join AOUSD
As an AOUSD General Member, you’ll have a seat at the table during discussion and development of new features to the OpenUSD specification. Through a structured and collaborative process, you’ll help shape the future features and directions of the OpenUSD technology stack and define the structure of the core functionality for how 3D worlds will be described and interacted with going forward.As an AOUSD General Member, you’ll have a seat at the table during discussion and development of new features to the OpenUSD specification. Through a structured and collaborative process, you’ll help shape the future features and directions of the OpenUSD technology stack and define the structure of the core functionality for how 3D worlds will be described and interacted with going forward.
Learn about participation in AOUSD Working Groups and Interest Groups
