> For the complete documentation index, see [llms.txt](https://carec.gitbook.io/carec-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://carec.gitbook.io/carec-docs/documentation/simulation/robot-description-and-tf-tree.md).

# Robot Description and TF Tree

CAREC needs one robot description that can be parameterized for simulation and hardware without changing frame names or navigation semantics.

```mermaid
flowchart TD
    map --> odom
    odom --> base_footprint
    base_footprint --> base_link
    base_link --> sensors["Sensor frames"]
    base_link --> wheels["Wheel and caster frames"]
```

## Required frames

| Frame            | Responsibility                   | Publisher                                 |
| ---------------- | -------------------------------- | ----------------------------------------- |
| `map`            | Globally stable navigation frame | SLAM or localization                      |
| `odom`           | Locally continuous motion frame  | State estimator or odometry               |
| `base_footprint` | Ground-projected wheelchair pose | Robot state/localization stack            |
| `base_link`      | Main body reference              | Robot description                         |
| Sensor frames    | Optical or measurement origins   | Static transforms / robot state publisher |
| Wheel joints     | Drive and steering/caster state  | Joint state broadcaster                   |

Follow REP-103 axis conventions and use optical-frame conventions for cameras. Do not publish the same transform from two nodes.

## Description model

* Use Xacro for dimensions, variants, and sensor options.
* Separate visual meshes from simplified collision geometry.
* Model the occupied envelope and protruding components conservatively.
* Represent drive wheels with measured radius and separation.
* Include caster geometry when it materially affects collision or dynamics.
* Keep inertial values physically plausible; zero or near-zero inertia produces unstable simulation.

## TF acceptance checks

The tree must be connected, free of loops, free of duplicate publishers, timestamp-consistent with `/clock`, and available before navigation activates. CI should render the frame graph and fail on missing required frames.


---

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