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Combining ROS 2 Bag Files with USD Scenes
Learn how to combine ROS 2 bag files and USD scenes in Isaac Sim to build fully reproducible simulations for debugging, testing, and synthetic data generation.
🧭 Why Reproducibility Matters in Simulation
In robotics and autonomy, repeatability is everything. You need to:
- Debug a bug that only happens once.
- Re-run a scenario across multiple AI versions.
- Benchmark performance in consistent conditions.
- Generate synthetic data at scale.
To do that, you need a way to freeze your entire simulation state. That’s where the combination of ROS 2 bag files and USD scenes becomes so powerful.
🧳 What Each Component Captures
| Asset Type | What It Captures | Format |
| ------------- | -------------------------------------------------------- | ------------------------ |
| **ROS 2 Bag** | Sensor data, control commands, robot state, topic timing | `.db3`, `.yaml` |
| **USD Scene** | 3D world layout, physics, lighting, sensor configuration | `.usd`, `.usda`, `.usdc` |
Together, they let you replay exactly what the robot did, saw, and felt, in exactly the world it happened in.
🛠️ How to Set It Up
1. Record the Bag File
While running a robot in Isaac Sim:
ros2 bag record -a
This captures all topics: LiDAR, camera, IMU, /cmd_vel, /joint_states, etc.
2. Save the USD Stage
In Omniverse Isaac Sim:
- Go to the top menu →
File > Save As - Save the
.usdfile representing the full environment and robot pose at the moment of recording.
You now have a static snapshot of the physical world.
3. Replay the Data
Reload the saved .usd stage and replay the bag:
ros2 bag play <bag_name>
This re-publishes the same sensor/control data while the robot lives in the same virtual world geometry. Isaac Sim receives these messages as if the robot is acting live.
🎯 Use Cases
| Use Case | Benefit |
| ----------------------------- | --------------------------------------------------------------------------------- |
| **AI Regression Testing** | Re-test the same scenario across model versions |
| **Simulation Debugging** | Reproduce bugs with full visual + sensor context |
| **Synthetic Data Generation** | Generate new camera images or point clouds from different lighting or camera rigs |
| **Sim-to-Real Transfer** | Validate that real-world runs can be simulated and matched in Isaac |
| **Scenario Variation** | Change the USD (e.g., object pose) but replay same bag for robustness testing |
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