Tardigrade Unity Sim

Unity project for the Tardigrade pool scene. This is the ROS-TCP-Connector based simulator backend described in tardigrade_ws/docs/unity_simulation_plan.md — see that doc for the full architecture. This README covers what actually lives in this project and how to change robot movement/paths.

Setup

1. Install the same Editor version as ProjectSettings/ProjectVersion.txt.
2. Open the project once so packages resolve (com.unity.robotics.ros-tcp-connector and com.unity.robotics.visualizations are pulled from GitHub via Packages/manifest.json).
3. Robotics → Generate ROS Messages, pointed at tardigrade_ws/src/tardigrade_interfaces, generates the C# types under Assets/RosMessages/TardigradeInterfaces/. Re-run this whenever a .msg or .srv file changes in tardigrade_interfaces.
4. Robotics → ROS Settings → Protocol ROS2, IP 127.0.0.1, Port 10000 (matches ros_tcp_endpoint's default in the ROS workspace).

Running The Simulator

Start ros_tcp_endpoint in the tardigrade_ws Docker container:

cd /ws && source install/setup.bash
ros2 run ros_tcp_endpoint default_server_endpoint --ros-args \
  -p ROS_IP:=0.0.0.0 -p ROS_TCP_PORT:=10000

Press Play in the Unity Editor, then drive the robot from ROS — see tardigrade_ws/docs/local_sim_backend.md for path_follower and mission usage. Nothing on the ROS side needs to know whether it's talking to Unity or the fake backend; the topic contract is identical.

How The Unity Scene Is Split

SampleScene uses a hybrid authored/runtime layout. Physical arrangement and appearance are visible in Edit Mode; scripts configure changing scenario state when Play Mode begins.

SampleScene
├── SimulationEnvironment
│   ├── AcceptancePoolCollisions  (PoolEnvironment prefab)
│   ├── GateAcceptance            (Gate prefab)
│   └── UnderwaterEffects         (water, pool lights, particulate)
└── TardigradeRoot
    ├── Rigidbody + collider
    ├── RosRobotBridge + AuvPhysicsPlant
    ├── UnderwaterEnvironment + StereoCameraPublisher
    ├── Sensors                    (inspectable sensor mounting frames)
    └── tardigrade                 (visual FBX model)

The imported lowercase tardigrade is presentation only. TardigradeRoot owns the one Rigidbody and the vehicle transform, preventing individual FBX mesh pieces from becoming separate physical bodies.

The pool, gate, water, lighting, particle system, robot collider, and sensor mounts are saved in the scene or under Assets/Prefabs/Simulation. Runtime scripts still own:

• scenario selection and reset pose,
• water current and visual profile,
• sensor noise, delay, drift, and dropout,
• thruster state and failures,
• ROS transport and simulation clock,
• temporary left/right camera renderers.

RosRobotBridge is the composition and ROS lifecycle component. AuvPhysicsPlant applies buoyancy, six-axis damping, and distributed thruster forces to the serialized Rigidbody at 100 Hz. Canonical physical values come from Assets/StreamingAssets/tardigrade_vehicle.json, rather than being copied into scene objects.

The Scene view is the free editor camera. The Game view is the output of the vehicle-mounted camera, so the two views are expected to look different.

To rebuild the authored assets after changing their procedural templates, use Tardigrade → Rebuild Authored Simulation Scene. This recreates the three simulation prefabs and their materials, reconnects SampleScene, and is safe to run repeatedly.

Mission paths and control remain on the ROS side. Unity consumes normalized per-thruster commands and publishes raw simulated sensors and simulation-only ground truth.

Assets/Editor/ CLI Helpers

Headless-automation scripts, useful for CI or re-running setup without opening the Editor UI (Unity.exe -batchmode -nographics -quit -projectPath <proj> -executeMethod <Class>.<Method>):

• CliMessageGen.GenerateTardigradeInterfaces: same as Robotics → Generate ROS Messages, scripted against tardigrade_ws/src/tardigrade_interfaces.
• CliAttachBridge.ListSceneObjects / CliAttachBridge.AttachToRobot: lists the scene hierarchy, or finds the GameObject named tardigrade and attaches RosRobotBridge to it, saving the scene. Useful after rebuilding the scene from a new robot model import.
• SimulationSceneAuthoring.Run: rebuilds the simulator prefabs, materials, sensor mounts, and serialized scene references.
• SimulationBatchValidation.Run: validates configuration and coordinate/frame assumptions.
• SimulationPlayModeValidation.Run: runs the acceptance-scene smoke test.