USD Reference

This page lists the main USD elements, hierarchy, and support status currently covered by the MotrixSim USD loading path.

Note

Here, “supported” means the converter reads the USD schema or attribute and maps it to an existing MSD / MotrixSim semantic. This page is the current converter support contract, not a complete USD / Omni schema attribute index. For schemas marked as “partial”, only the listed subset and major known gaps are covered. USD / PhysX / Omni schemas or attributes that are not listed should not be assumed to work. Unsupported attributes are usually reported as warnings, or skipped when no usable data is available.

Status Legend

Marker	Meaning
Supported	Core semantics are converted and are recommended for current use
Partial	Only the listed subset is guaranteed, or some attributes are ignored / warned
Unsupported	Not currently converted to MotrixSim semantics

Index

USD Stage / Assets Partial

• Loader entry points Supported
• Files, layers, asset paths, remote textures Partial

Scene Prim Hierarchy Partial

• UsdGeom.Xform / instance / instance proxy Supported
• UsdPhysics.Scene / rigid body attributes Partial
• UsdPhysics.RigidBodyAPI Partial
• UsdPhysics.MassAPI Supported
• ArticulationRootAPI Partial
• UsdPhysics.Joint family Partial
• UsdGeom.Gprim geometry Partial
• UsdLux.LightAPI lights Partial

Joints / Drives Partial

• FixedJoint, RevoluteJoint, PrismaticJoint, SphericalJoint Supported
• PhysicsDriveAPI:angular, PhysicsDriveAPI:linear Partial
• DistanceJoint, PhysicsDriveAPI:transX/rotX... Unsupported

Geometry / Meshes / Collision Partial

• Mesh, Cube, Cylinder, Capsule, Sphere, Plane Supported
• GeomSubset, normals, st texcoords Partial
• CollisionAPI, MeshCollisionAPI, FilteredPairsAPI Partial
• boundingSphere, boundingCube, convexDecomposition Supported

Materials / Textures Partial

• OmniPBR, OmniGlass, UsdPreviewSurface Partial
• PhysicsMaterialAPI, PhysX compliant contact material Partial
• Unknown shader ids Unsupported

Lights / Environment Partial

• DistantLight, SphereLight, RectLight Supported
• DomeLight ambient / HDR skybox Partial

Unsupported Domains Unsupported

• camera, sensor, tendon, deformable, particle, time-sampled animation schemas

Entry Points

USD / API element	Status	MotrixSim mapping
motrixsim.load_model(path)	Supported	Convert USD and return SceneModel
motrixsim.msd.from_file(path)	Supported	Convert USD and return editable / composable msd.World

Stage, Files, and Assets

USD element / feature	Status	MotrixSim mapping
.usd / .usda / .usdc / .usdz	Supported	Opened through OpenUSD Stage.Open
sublayer / reference / payload	Partial	Expanded by OpenUSD; the converter handles the composed prims
resolved texture path	Supported	Converted to MSD texture file source
relative texture path	Supported	Resolved relative to the USD file directory
remote texture URL	Partial	Downloaded into a local cache before conversion
time-sampled stage animation	Unsupported	Currently reads the static scene at the default time

Scene Hierarchy and Transforms

USD element / attribute	Status	MotrixSim mapping
UsdGeom.Xform hierarchy	Supported	Traverses scene hierarchy and accumulates world transforms
instance / instance proxy	Supported	Traverses instance proxy children
visibility = invisible	Supported	Does not create visual geometry
purpose = guide	Supported	Does not create visual geometry; still creates collision geometry when the prim is a collider
scale / non-uniform scale	Supported	Applied to geometry size or mesh_scale
negative scale	Supported	Flips mesh winding to keep face orientation correct
UsdPhysics.RigidBodyAPI	Partial	Creates Link / Body; non-kinematic top-level rigid bodies get FreeJoint
kinematic rigid body	Supported	Treated as a static link without a free joint
ArticulationRootAPI	Partial	Used to inherit self-collision settings

Physics Scene and Rigid Body Attributes

USD element / attribute	Status	MotrixSim mapping
UsdPhysics.Scene.gravityDirection + gravityMagnitude	Supported	simulate_option.gravity
physxScene:timeStepsPerSecond	Supported	simulate_option.timestep
UsdPhysics.MassAPI	Supported	Reads the MassAPI attributes below
MassAPI.mass	Supported	link.inertial.mass
MassAPI.centerOfMass	Supported	link.inertial.pos
MassAPI.diagonalInertia	Supported	link.inertial.diag_inertia
MassAPI.principalAxes	Supported	link.inertial.orientation
MassAPI.density	Supported	Collider physics_material.density
physxRigidBody:disableGravity	Supported	link.gravcomp = 1.0
physxRigidBody:linearDamping / angularDamping	Unsupported	Reported as warnings
physxRigidBody:maxLinearVelocity / maxAngularVelocity	Unsupported	Reported as warnings
physxRigidBody:enableCCD / retainAccelerations	Unsupported	Reported as warnings

Non-finite values and non-positive mass values are ignored with warnings. This group is still marked as “partial” in the index because the PhysX rigid-body extension attributes have unsupported gaps; the listed MassAPI attributes themselves are converted.

Joints and Drives

USD joint / attribute	Status	MotrixSim mapping
FixedJoint	Supported	Converted to a fixed child link with no DOF
RevoluteJoint	Supported	JointType.Revolute; supports X/Y/Z axis, limits, and reference pose
PrismaticJoint	Supported	JointType.Slide; supports X/Y/Z axis, limits, and reference pose
SphericalJoint	Partial	JointType.Ball; cone angles are approximated as a ball joint limit
DistanceJoint	Unsupported	Reported as a warning
PhysicsDriveAPI:angular	Partial	Applies to revolute joint spring-damper and actuator force limit
PhysicsDriveAPI:linear	Partial	Applies to prismatic joint spring-damper and actuator force limit
drive:maxForce	Supported	joint.actuator_force_limit, and creates MotorActuator.forcerange for one-DOF joints
drive:targetPosition	Supported	Spring target
drive:stiffness / drive:damping	Supported	Joint spring-damper
physxJoint:jointFriction	Supported	joint.friction_loss
physxJoint:armature	Supported	joint.armature
joint:collisionEnabled = false	Supported	Creates a parent-child link collision ignore
PhysicsDriveAPI:transX/transY/transZ/rotX/rotY/rotZ	Unsupported	Reported as warnings
physxJoint:maxJointVelocity	Unsupported	Reported as a warning

Geometry, Meshes, and Collision

USD geometry / attribute	Status	MotrixSim mapping
UsdGeom.Mesh	Partial	ShapeType.Mesh, with mesh data stored inline in MeshAsset.source = MeshSource::Buffer
Cube	Supported	ShapeType.Box
Cylinder	Supported	ShapeType.Cylinder
Capsule	Supported	ShapeType.Capsule
Sphere	Supported	ShapeType.Sphere
Plane	Supported	ShapeType.Plane
GeomSubset with elementType = "face"	Supported	Splits into per-face-subset submeshes and can preserve subset materials
normals / st texcoords: vertex / varying / faceVarying	Supported	Read and expanded into MSD mesh data
Other normal / texcoord interpolation modes	Unsupported	Reported as warnings
CollisionAPI	Supported	Creates a collider
MeshCollisionAPI	Partial	Can create a mesh collider; only the approximation values below are supported
MeshCollisionAPI.approximation = none	Supported	Default mesh collider
convexHull	Supported	Default mesh collider, without runtime ACD
boundingSphere	Supported	Creates a sphere collider from mesh bounds
boundingCube	Supported	Creates a box collider from mesh bounds; can also preserve the visual mesh
convexDecomposition	Supported	Marks the mesh asset as collision_cooking = ConvexDecomposition and enables CoACDConfig
Unknown MeshCollisionAPI.approximation	Unsupported	Warns and falls back to the default mesh collider
FilteredPairsAPI	Supported	Creates collision ignore pairs
physxCollider:contactOffset	Supported	geometry.margin
physxCollider:restOffset	Unsupported	Reported as a warning
MotrixPhysicsGeomAPI	Supported	Supports Motrix custom impedance contact model and priority

Physics Materials, Visual Materials, and Textures

USD material / shader	Status	MotrixSim mapping
PhysicsMaterialAPI.staticFriction	Supported	Sliding friction; torsional / rolling friction use fixed ratios
PhysicsMaterialAPI.dynamicFriction	Supported	Fallback when static friction is not authored
PhysicsMaterialAPI.density	Supported	Collider density, lower priority than MassAPI.density
PhysicsMaterialAPI.restitution	Supported	Hard contact restitution
physxMaterial:compliantContactStiffness / Damping	Supported	Force spring or acceleration spring contact model
physxMaterial:compliantContactAccelerationSpring	Supported	Selects acceleration spring
physxMaterial:dampingCombineMode / frictionCombineMode / restitutionCombineMode	Unsupported	Reported as warnings
OmniPBR	Partial	Converts only diffuse / opacity texture merge, diffuse tint, emissive, metallic, roughness, specular level, normal, detail normal, opacity threshold, texture scale / translate
OmniGlass	Partial	Converts only glass color, IOR, reflection color, and roughness; outputs a transparent non-metallic material
UsdPreviewSurface	Partial	Converts only diffuse color / texture, normal, emissive, metallic, roughness, IOR, and UsdTransform2d texture transform
Parseable local MDL material	Partial	Can fall back from local MDL parameters to OmniPBR / OmniGlass mappings
MaterialBindingAPI	Supported	Binds visual material or physics material
doubleSided	Partial	Affects both_side; alpha-blended materials have depth-sorting protection
Unknown shader id	Unsupported	Reported as a warning

Lights and Environment

USD light	Status	MotrixSim mapping
DistantLight	Supported	Directional light
SphereLight	Supported	Point light
RectLight	Supported	Rect light; preserves width, height, axes, normalize flag, color, and exposure-applied intensity
Large RectLight	Supported	Adds capped ambient brightness
DomeLight without texture	Supported	Ambient light
DomeLight with .hdr texture	Partial	Bakes IBL maps and registers a skybox texture
Other light types	Unsupported	No MotrixSim light is currently generated

When a scene contains USD lights, the default head light is disabled to avoid double illumination. Converted worlds enable SSGI by default.

Current Unsupported or Uncovered Domains

USD / PhysX domain	Status	Notes
UsdGeom.Camera	Unsupported	Not currently converted to MotrixSim camera
sensor schemas	Unsupported	Not currently converted to MotrixSim sensors
tendon / cable / actuator-like USD schemas	Unsupported	Only a subset of joint drives converts to motor actuators
deformable / particle / cloth	Unsupported	Not handled by the current USD conversion path
time-sampled animation	Unsupported	Currently reads static scenes
Unknown material shaders, unresolved textures, or abnormal mesh data	Partial	May be warned, skipped, or degraded

For complex USD assets, enable logging during loading and inspect warnings before physics validation.