Robot-Body-Isaac Profile USD Authoring Guide

This document describes how to author a USD asset that conforms to the Robot-Body-Isaac profile. It consolidates the required feature set, USD properties, naming conventions, and robot-specific composition requirements.

Profile definition

The Robot-Body-Isaac profile includes the following feature set (see robot_body_isaac.toml and the feature dependency graph). Each feature’s requirements and dependencies are defined in the feature specifications.

[Robot-Body-Isaac]
"1.0.0" = {features = [
    {"FET_001_STANDARD" = {version = "0.1.0"}}, # Minimal
    {"FET_003_STANDARD" = {version = "0.1.0"}}, # RBD Physics (Standard)
    {"FET_004_ROBOT_PHYSX" = {version = "0.1.0"}}, # Multi-body physics (Robot PhysX)
    {"FET_021_ISAAC" = {version = "0.2.0"}}, # Robot Core (Isaac)
    {"FET_022_ISAAC" = {version = "0.1.0"}}, # Driven Joints (Isaac)
    {"FET_024_PHYSX" = {version = "0.1.0"}}, # Articulation
    {"FET_100_ISAAC" = {version = "0.1.0"}}, # Isaac composition
]}
"1.2.0" = {features = [
    {"FET_001_STANDARD" = {version = "0.1.0"}}, # Minimal
    {"FET_003_PHYSX" = {version = "0.4.0"}}, # RBD Physics (PhysX)
    {"FET_004_PHYSX" = {version = "0.4.0"}}, # Multi-body physics (PhysX)
    {"FET_021_ISAAC" = {version = "0.2.0"}}, # Robot Core (Isaac)
    {"FET_022_ISAAC" = {version = "0.2.0"}}, # Driven Joints (Isaac)
    {"FET_024_PHYSX" = {version = "0.1.0"}}, # Articulation
    {"FET_101_ISAAC" = {version = "0.1.0"}}, # Robot Isaac composition
]}

Version 1.2.0 notes

Version 1.2.0 pins the PhysX rigid-body/multibody contract (FET_003_PHYSX@0.4.0, FET_004_PHYSX@0.4.0) and adopts the robot Isaac composition feature FET_101_ISAAC@0.1.0 in place of the prop-oriented FET_100_ISAAC. FET_101_ISAAC routes robot assets to the standalone simready.asset_transformer robot transform (simready_physx_to_isaac_robot), so the composed asset carries the Isaac robot schema (IsaacRobotAPI, isaac:physics:robotLinks, isaac:physics:robotJoints) required by the FET_021_ISAAC robot-core checks.

Required USD properties and schemas

Stage metadata (required)

• defaultPrim must be set on every layer.

• upAxis = "Z" and metersPerUnit = 1 must be set on every stage.

PhysX rigid bodies and colliders (required)

• Apply PhysicsRigidBodyAPI to any simulated rigid body prim.

• Apply PhysicsCollisionAPI to collision-enabled prims.

• Author physics:approximation = "sdf" for PhysX collider approximation.

• Rigid body prims must be UsdGeomXformable.

Multi-body joints (required)

• Use UsdPhysicsJoint prims (or subtypes) to connect rigid bodies.

• Author rel physics:body0 and rel physics:body1 relationships.

• Apply PhysxJointAPI when authoring PhysX-specific joint properties.

Driven joints (required)

• Apply PhysicsDriveAPI:* or PhysxMimicJointAPI:* to driven joints.

• Apply PhysicsJointStateAPI:* to driven joints.

• Author physxJoint:maxJointVelocity with a positive value.

• When a joint has both drive and mimic APIs, drive stiffness and damping must be exactly 0.0.

• Mimic joints must set a single valid physxMimicJoint:*:referenceJoint and author physxMimicJoint:*:gearing, physxMimicJoint:*:naturalFrequency, and physxMimicJoint:*:dampingRatio.

Robot schema (required)

Apply IsaacRobotAPI to the default prim and populate robot relationships:

• apiSchemas includes IsaacRobotAPI

• isaac:namespace

• isaac:physics:robotJoints relationship

• isaac:physics:robotLinks relationship

Articulation root (required)

Apply PhysicsArticulationRootAPI to the root prim of the articulation:

def Xform "Robot" (
    prepend apiSchemas = ["PhysicsArticulationRootAPI"]
)
{
}

Robot composition requirements

Robot core requirements enforce a modular layout for physics data and a clean asset folder structure.

Physics layer separation

• Author physics schemas and physics attributes in the physics layer only.

• Keep base/visual layers free of physics schemas and physics attributes.

Clean folder layout

• Robot asset folders must not contain unreferenced files.

• Keep the interface layer at the root, with subfolders for payloads.

Example layout:

Manufacturer/
  robot.usd
  Payload/
    material.usda
    base.usda
    geometry.usdc
    instances.usda
    Physics/
      physics.usda
      physx.usda

No overrides

• Author changes in source layers, not session or override layers.

• Avoid muting or overriding schema-defining layers.

Thumbnail requirement

• Provide a thumbnail at .thumbs/256x256/{robot name}.png.

Naming conventions

Robot naming

• Use lowercase, underscore-separated file names.

• Use stable prim paths for robot roots and joints.

Prim naming

• Choose either camelCase or snake_case and use it consistently.

• Avoid spaces, special characters, and reserved keywords.

• Use descriptive, purpose-driven names.

• Use prefixes by prim type when appropriate (e.g., mesh_, material_).

File naming

• Use lowercase file names.

• Use .usd, .usda, .usdc, or .usdz as appropriate.

• Use underscores or hyphens; avoid spaces and special characters.

• Avoid reserved names (e.g., CON, PRN, AUX, NUL).

• Use version numbers when appropriate (e.g., _v1.0).

Validation metadata (recommended)

Include profile metadata in customLayerData to simplify validation workflows:

customLayerData = {
    dictionary SimReady_Metadata = {
        dictionary validation = {
            string profile = "Robot-Body-Isaac"
            string profile_version = "1.0.0"
        }
    }
}

References

• Feature dependency graph — requirements and dependencies for all features

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/profiles/robot_body_isaac.toml

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_021_ISAAC.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_022_STANDARD.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_024_STANDARD.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/robot-schema.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/robot-naming.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/clean-folder.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/no-overrides.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/thumbnail-exist.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/verify-robot-physics-attribute-source-layer.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/isaac_sim/robot_core/requirements/verify-robot-physics-schema-source-layer.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/base_articulation/requirements/has-articulation-root.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/physics_driven_joints/requirements/physics-joint-has-drive-or-mimic-api.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/physics_driven_joints/requirements/physics-joint-max-velocity.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/physics_driven_joints/requirements/drive-joint-value-reasonable.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/physics_driven_joints/requirements/mimic-api-check.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/core/naming_paths/requirements/prim-naming-convention.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/core/naming_paths/requirements/file-naming-convention.md