Sensor-IMU Profile USD Authoring Guide#

This document describes how to author a USD asset that conforms to the Sensor-IMU profile.

Sensor-IMU is a sensor profile: it validates the IMU sensors an asset carries, not the asset itself. Stamp it alongside the asset’s primary profile (Robot-Body, Robotics-Prop, or whichever profile matches the host asset — see the profile index). An asset that carries several sensor types is stamped with one sensor profile per type.

Validating an asset against this profile requires both the Sensors tier and the Core tier:

pip install simready-validate simready-foundation-tier-sensors simready-foundation-tier-core

Profile definition#

The Sensor-IMU profile contains a single feature (see profiles.toml alongside this document, and the feature dependency graph):

[Sensor-IMU]
"1.0.0" = {features = [
    {"FET_034_ISAAC" = {version = "0.1.0"}}, # "IMU Sensor"
]}

FET_034_ISAAC defines the simulation-readiness contract for IMU sensor prims. It has no feature dependencies, so this profile checks IMU wiring only. Everything else about the asset — units, hierarchy, physics, materials, packaging — comes from whichever primary profile the asset is also stamped with.

What the profile checks#

Requirement

Capability

Summary

PS.001

Physics Bodies/Physics Sensors

An IsaacImuSensor prim must be a descendant of a prim with PhysicsRigidBodyAPI applied.

The check applies only to the IsaacImuSensor prims a stage actually contains. An asset with no IMU sensor passes this profile without asserting anything. A passing result therefore means “every IMU present is wired correctly”, not “this asset has a working IMU” — confirm the sensor exists before treating conformance as evidence that it does.

Required USD authoring#

An IsaacImuSensor reads forces and velocities from the physics engine. The engine reports those quantities per rigid body, so the sensor only receives data when it sits underneath one. A sensor authored outside a rigid body loads without error and reports nothing at runtime, which is why this is checked statically.

Place the sensor as a child or deeper descendant of the prim that carries PhysicsRigidBodyAPI. An ancestor relationship is required; a sibling does not satisfy PS.001.

# Valid: the sensor is under a rigid body
def Xform "Robot"
{
    def Xform "Base" (
        prepend apiSchemas = ["PhysicsRigidBodyAPI"]
    )
    {
        def IsaacImuSensor "IMU" {}
    }
}

# Invalid: no rigid body ancestor, so the sensor receives no physics state
def Xform "Robot"
{
    def IsaacImuSensor "IMU" {}
}

Mount the sensor at the pose it occupies on the physical robot. The profile does not check placement, so an IMU authored at the body origin passes validation while producing accelerations that do not match the real device.

Validation#

A sensor profile is validated in its own run. “Stamping both profiles” means validating the asset against each one; there is no combined invocation:

simready-validate --profile Robotics-Prop --version 4.0.0 path/to/asset.usd
simready-validate --profile Sensor-IMU --version 1.0.0 path/to/asset.usd

Both runs must pass. The sensor profile is not a substitute for the primary one — on its own it says nothing about units, hierarchy, physics, materials, or packaging.

If you record the result in the optional validation dictionary under SimReady_Metadata, note that the documented form holds a single profile and profile_version. Record the primary profile there and track sensor conformance alongside it; the metadata has no multi-profile form today.

Runtime verification#

Static validation confirms the sensor is wired to a rigid body. It cannot confirm the sensor produces data. The Benchmark test imu_sensor_data checks that the sensor reports non-zero angular velocity and linear acceleration during physics simulation:

pip install "simready-foundation-tier-sensors[benchmark]"
simready-benchmark --features FET_034_ISAAC

The [benchmark] extra installs the Benchmark engine; a validator-only tier install does not include it.

Samples#

  • Passing: sample_content/common_assets/sensors/physics_sensors/IMUSensorCheckerPass.usda

  • Failing: sample_content/common_assets/sensors_fails/physics_sensors/IMUSensorCheckerFail.usda

References#