Universal Scene Description (USD)

Experimental

USD (Universal Scene Description) is a 3D file format developed by Pixar for exchanging and assembling complex scenes, covering geometry, structure, materials and animation. Unlike simpler interchange formats, USD also defines a powerful system for layering and composing assets, which is not yet covered by instant3Dhub.

🔍 See 3D Data Resources for details and definitions.

Extensions

  • .usd: Standard USD file format, either ASCII or binary

  • .usda: Human-readable ASCII (UTF-8 text)

  • .usdc: Binary format (compact, random-access)

  • .usdz: Package/zip archive bundling USD + external assets

Structure

USD organizes data into a hierarchical scenegraph of Prims (primitives). Prims can contain child Prims, attributes, and references, which naturally represent assemblies and part hierarchies.

USD also defines the concepts of

  • Models (logical chunks of the hierarchy) and

  • Assets (external references)

to manage large or composed scenes. Through composition operators such as references, inherits, and variants, complex assemblies can be built across multiple files.

Geometry

USD defines several geometric primitives (Gprims) that cover common entities for visualization:

  • Meshes: polygonal meshes (UsdGeomMesh)

  • Curves & Patches: NURBS patches, basis curves, NURBS curves

  • Points: point sets and particles

  • Intrinsic solids: capsule, cone, cube, cylinder, sphere (mainly used as proxy volumes in pipelines)

Additional properties include:

  • Primvars: per-vertex or per-face attributes (normals, colors, UVs, etc.)

  • Attributes additional geometry properties such as:

    • Extent: defines the bounding box of the geometry

    • Visibility: controls whether a Prim is visible or hidden

Tesselation

instant3Dhub supports tessellated geometry only via UsdGeomMesh (polygonal meshes, including subdivision surfaces). Meshes can include primvars such as normals, UVs, and colors, which are used for visualization.

Other tessellated primitives defined in USD (curves, NURBS patches, intrinsic solids like cube, sphere, capsule, cone, cylinder) are not mapped in instant3Dhub.

B-Rep

USD does not support exact CAD geometry.

PMI & Model Views

PMI and Model Views are not supported in USD.

Metadata

USD allows attaching metadata to Prims and properties. Metadata is not yet supported by instant3Dhub.

Service Negotation Key

  • model/vnd.usda

  • model/vnd.usdz+zip

Miscellaneous

Future USD-related aspects under consideration for instant3Dhub:

  • Layers

  • Enabled States

  • Light Sources

  • Camera Positions

  • Interpolators (e.g. for cameras or meshes)

  • Keyframe Animations

  • Textures and PBR materials

External Resources

OpenUSD



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