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