URDF USD Converter v0.1.0

0.1.0

Features

• Added support for the local file:// protocol for external references (meshes and textures)
• Applied all current Newton USD Schemas (v0.1.0) alongside UsdPhysics schemas
  • URDF joint mimics are now converted via NewtonMimicAPI

Fixes

• Corrected inertia calculations to be consistent across platforms during eigenvector decomposition

Dependencies

• Updated to usd-exchange>=2.2.2
• Updated to newton-usd-schemas>=0.1.0

URDF USD Converter v0.1.0rc2

Features

• Added support for the local file:// protocol for external references (meshes and textures)

Fixes

• Corrected inertia calculations to be consistent across platforms during eigenvector decomposition

Dependencies

• Updated to usd-exchange>=2.2.2
• Updated to newton-usd-schemas>=0.1.0rc3

URDF USD Converter v0.1.0rc1

Features

• Applied all current Newton USD Schemas (v0.1.0rc2) alongside UsdPhysics schemas
  • URDF joint mimics are now converted via NewtonMimicAPI

URDF USD Converter v0.1.0b1

Features

• Calibration, Dynamics, Safety Controller, and Mimic are all converted as custom attributes on the Joint prim
• Convert custom elements as Scopes and custom attributes with custom and urdf: namespace
• Adapted link handling for URDF's "ghost link" convention, where the first link may be a
  purely used to identifiy fixed vs floating articulations

Fixes

• Stopped triangulating OBJ meshes to support n-gons
• Fixed handling of URDF materials with no material name

Documentation

• Added benchmarks reporting for several URDF datasets
• Added documentation on how to specify ROS packages

URDF USD Converter v0.1.0a2

Features

• Added conversion of DAE embedded materials to UsdPreviewSurface materials
• Improved performance by optimizing numpy processing when converting STL, OBJ, and DAE meshes

Fixes

• Fixed several DAE mesh conversion issues
  • Fixed to correctly parse even when the DAE file structure is corrupted
  • Fixed an issue where the UV array could not be acquired correctly in some cases
  • Fixed familyType attribute when meshes contain subsets
• Fixed OBJ per-face material assignments via UsdGeomSubsets
• Fixed material overrides beween native URDF & embedded OBJ/DAE materials
  • We now match rviz & urdfviewer where embedded OBJ/DAE materials take priority over URDF materials
• Fixed texture wrapping behaviour using repeat mode on all UsdUvTexture shaders
  • The wrapMode is exposed on the material interface so users can change it as needed
• Fixed color issue related to the specular workflow
  • Specular workflow has been unconditionally disabled. There is no meaningful mapping of URDF specular color (phong based materials) to UsdPreviewSurface (simplistic PBR based materials) so we ignore specular color for now. This gives results more closely matching rviz & urdfviewer
• Fixed URDF Parser to allow invalid axis specification on fixed joints
  • Many sample assets have axis="0 0 0" on fixed joints, which is meaningless but harmless
• Fixed URDF Parser to handle errors when no links exist in the file

Documention

• Update Concept Mapping document to reflect new stance on material overrides

URDF USD Converter v0.1.0a1

Features

• USD Asset Structure
  • Output Assets are completely standalone with no dependencies on the source URDF, OBJ, DAE, or STL files
  • Atomic Component structure with Asset Interface layer and payloaded contents
  • Separate geometry, material, and physics content layers for easy asset-reuse across domains
  • Library-based asset references for meshes and materials to avoid heavy data duplication
  • Explicit USD stage metadata with units (meters, kilograms) and up-axis (Z)
• Link Conversion
  • URDF links are converted as UsdGeom.Xform prims with UsdPhysics.RigidBodyAPI applied
  • The root link has UsdPhysics.ArticulationRootAPI applied to indicate the root of the kinematic tree
  • Links are nested in USD, reflecting the kinematic hierarchy of the source URDF rather than the XML file structure
  • Complete mass properties including explicit inertia & center of mass via UsdPhysics.MassAPI
• Joint Conversion
  • Revolute joints as UsdPhysics.RevoluteJoint with angular limits
  • Continuous joints as UsdPhysics.RevoluteJoint without limits
  • Prismatic joints as UsdPhysics.PrismaticJoint with linear limits
  • Fixed joints as UsdPhysics.FixedJoint
  • Planar joints as UsdPhysics.Joint with the appropriate UsdPhysics.LimitAPI applied to constrain the locked DOFs
  • Floating joints (bodies are free by default in USD)
  • All joints have automatic joint frame alignment between Body0 and Body1, accounting for URDF joint axis, position, and orientation.
  • Joint limits for velocity & effort have no equivalent in UsdPhysics, but are authored as custom attributes urdf:limit:velocity and urdf:limit:effort respectively.
• Geometry Conversion
  • All visual and collision geometry is converted to USD
    • Visuals are set with default UsdPurpose and colliders with guide UsdPurpose
  • UsdPhysics.CollisionAPI is applied to colliders
  • Meshes as UsdGeom.Mesh
    • Automatic mesh library generation with reference-based asset structure, to avoid duplicate topology
    • STL files converted to USD using numpy-stl and usd-exchange with normal processing
    • OBJ files converted using tinyobjloader and usd-exchange with UV coordinates and normal mapping
    • DAE files converted using pycollada and usd-exchange with UV coordinates, normal mapping, and UsdGeom.Subset support
    • OBJ and DAE files specifying multiple meshes convert as a list of meshes under a common parent prim
    • UsdPhysics.MeshCollisionAPI is applied to mesh colliders with convex hull specified as the approximation preference
  • Spheres as UsdGeom.Sphere
  • Boxes as UsdGeom.Cube with scale transforms
  • Cylinders as UsdGeom.Cylinder
• Visual Material and Texture Conversion
  • All materials are converted to UsdShade.Material graphs using UsdPreviewSurface shaders, and encapsulated as instanceable material interfaces
  • PNG texture support with automatic texture copying and path resolution
  • URDF materials convert rgba as diffuse color and opacity, with support for diffuse textures
  • OBJ embedded materials (MTL files) convert diffuse color, specular color, dissolve (opacity), roughness (not shininess), metallic, and ior
    • diffuse, specular, normal/bump, roughness, metallic, and opacity textures are all supported
• Prim Naming
  • If URDF/DAE/OBJ names are not valid USD specifiers they are automatically transcoded & made unique & valid
  • Display name metadata preserves the original source names on the USD Prims
• Command Line Interface
  • Input is an URDF file and default output is a USD Layer as a structured Atomic Component with an Asset Interface USDA layer
    • All heavy data is compressed binary data (via USDC layers) while lightweight data is plain text for legibility
  • Optional comment string embedded into all authored USD Layers
  • Optional Stage flattening for single-file output
  • Optionally skip the UsdPhysics.Scene (this may be desirable for multi-asset setups)
  • Error handling with graceful failures
  • Enable verbose output for debugging (exposes any traceback info)
• Python API
  • Full programmatic access via urdf_usd_converter.Converter class with configurable parameters for all CLI flags
  • Enables interactive editing of the USD Layers after conversion

Known Limitations

USD Data Conversion

• Joint Conversion
  • Calibration has no equivalent in UsdPhysics and is omitted
  • Dynamics has no equivalent in UsdPhysics and is omitted
  • Safety Controller has no equivalent in UsdPhysics and is omitted
  • Mimic has no equivalent in UsdPhysics and is omitted
• Geometry Conversion
  • No other file formats beyond OBJ/DAE/STL are supported
  • For DAE files, only "TriangleSet", "Triangles", "Polylist", and "Polygons" are supported
  • For OBJ files, only objects with faces are supported (i.e. no points, lines, or free-form curves/surfaces)
• Visual Material and Texture Conversion
  • DAE embedded materials are not implemented
  • Projection shaders for basic geometry primitives (box, cylinder, sphere) are not implemented
  • More accurate PBR materials (e.g. OpenPBR via UsdMtlx) are not implemented
• Other Elements
  • Transmission conversion is not implemented
  • Gazebo conversion is not implemented
  • Conversion of other out-of-spec URDF extensions are not implemented

Using the USD Asset in other USD Ecosystem applications

• The USD Asset contains nested rigid bodies within articulations.
  • Support for nested bodies in UsdPhysics is fairly new (as of USD 25.11), and some existing applications may not support this style of nesting.