# ROS 2 tf2 transform listener and turtle-following node

Official ROS geometry tutorial node that spawns turtle2, looks up its transform relative to a target frame and publishes Twist velocity commands to follow that target. It is an installed ROS 2 console entrypoint with ROS graph effects, not a direct Python-file main or a verified robot controller.

ID: `ros2-tf2-listener`

Record version: `source-bb2c9f91a430216878a831f355f529761dadb8603e3e390ecf6ec9626fa4713f`

Hub commit: `1c4c1e1533ff364fd4a35cddc8750b9306b0a5ba`

## Access

Read the pinned node, package declarations and setup registration before configuring the intended ROS graph. This source reference does not install or execute code.

Optional inert file retrieval: `python /PATH_TO_SKILL/scripts/rsh.py fetch-source ros2-tf2-listener --expected-source-revision 8e677416092ac97606a4a23256c815ba2fe762d4 --expected-source-sha256 bb2c9f91a430216878a831f355f529761dadb8603e3e390ecf6ec9626fa4713f --project ./experiment --json`. This verifies one file, preserves provenance and never installs or runs it. See [source-file retrieval](https://hub.superfastrobotics.com/source-files.md).

Hub preparation adapter: **false**. Runtime verification: **not_run**.

Upstream setup: https://github.com/ros/geometry_tutorials/blob/8e677416092ac97606a4a23256c815ba2fe762d4/turtle_tf2_py/setup.py

## Source and license

- Repository: https://github.com/ros/geometry_tutorials
- Pinned source: https://github.com/ros/geometry_tutorials/blob/8e677416092ac97606a4a23256c815ba2fe762d4/turtle_tf2_py/turtle_tf2_py/turtle_tf2_listener.py
- Revision: `8e677416092ac97606a4a23256c815ba2fe762d4`
- Path: `turtle_tf2_py/turtle_tf2_py/turtle_tf2_listener.py`
- Source SHA256: `bb2c9f91a430216878a831f355f529761dadb8603e3e390ecf6ec9626fa4713f`
- Source bytes: 4419
- Original authors: Open Source Robotics Foundation, Inc.
- License: [Apache-2.0](https://github.com/ros/geometry_tutorials/blob/8e677416092ac97606a4a23256c815ba2fe762d4/LICENSE)
- License scope: Selected listener source under its explicit Apache-2.0 header, copyright 2021 Open Source Robotics Foundation, Inc. Preserve attribution, license and applicable notices. The package also declares BSD for other material; this source review does not clear the full package, dependencies or physical-robot use.

## Artifact

```json
{
  "kind": "code",
  "format": "python"
}
```

## Requirements

```json
{
  "python": null,
  "packages": [
    "Compatible ROS 2 rclpy environment with the context-manager init API used by this source",
    "tf2_ros",
    "geometry_msgs",
    "turtlesim_msgs",
    "Installed turtle_tf2_py package exposing the reviewed console entrypoint"
  ],
  "hardware": [],
  "system": [
    "Configured ROS graph providing the relative spawn service and appropriate turtle1/turtle2 transforms",
    "Reviewed namespace, target_frame parameter and intended turtle2/cmd_vel subscribers"
  ],
  "notes": "The package is labeled version 0.7.0 at a Rolling-branch source pin; neither label establishes a tested ROS distribution, Python version or operating system. The node defaults target_frame to turtle1, requests turtle2 at x=4.0, y=2.0, theta=0.0 and, after spawning, queries a transform into turtle2 with rclpy.time.Time(). On a nominal one-second timer it publishes angular z from atan2 and linear x as 0.5 times translation distance. The period and gains are source settings, not measurements. Transform failures are logged and return without an explicit zero-velocity stop. No obstacle check or speed clamp is present. This node does not generate its required transforms, and a single source file is insufficient. ROS graph dependencies, shutdown behavior, hardware remappings and compatibility remain untested."
}
```

## Invocation

```json
{
  "entrypoint": "ros2 run turtle_tf2_py turtle_tf2_listener",
  "notes": "Installed ROS 2 console command backed by the pinned setup.py registration turtle_tf2_py.turtle_tf2_listener:main. The source defines main without a __main__ guard; direct python-file execution is not the declared node invocation. Starting the console entrypoint initializes rclpy, calls a spawn service and can publish velocity commands to the configured graph. No physical-controller compatibility or safe stopping is established. The Hub supplies inert source metadata with no preparation/execution adapter and ran no ROS node or simulator."
}
```

## Compatibility

```json
[]
```

Missing environment fields remain unknown. Source discovery labels do not establish robot compatibility.

## Evidence

Level: **source_reviewed**. Runtime verification: **not_run**.

Complete node read as inert text and Python AST parsed without import or execution. Source, license, package XML and setup bytes matched SHA-256, lengths and immutable-tree Git blob pins. Installed console registration and ROS graph effects were inspected; no ROS/Python/OS combination, controller, simulator or task result was tested.

Source review and contributor reports do not establish task completion. Preserve upstream attribution and licenses.