Sdf

interface:
  display_name: "SDF"
  short_description: "Generate and validate SDFormat robot models."
  default_prompt: "Use $sdf to generate, update, and validate SDFormat/SDF robot or simulator models from Python sources, handing generated SDFs to $cad-viewer when available."


MIT License

Copyright (c) 2026 earthtojake

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


# SDF builder helpers

Builder helpers are optional. They exist to reduce common LLM mistakes in XML construction, not to replace SDFormat or libsdformat.

## Why helpers exist

LLMs often make these mistakes when writing raw XML:

- wrong pose value length;
- hidden degree/radian conversion;
- missing `relative_to` or `expressed_in`;
- zero or non-finite joint axes;
- negative primitive dimensions;
- mesh scale applied inconsistently;
- inertial values copied from visuals;
- plugin filenames invented from plausible names.

Helpers should make the common path explicit, typed-ish, and auditable while still returning ordinary `xml.etree.ElementTree.Element` nodes.

## Design constraints

- Standard library only.
- No mandatory Gazebo, ROS, NumPy, lxml, CAD, or mesh dependency.
- Return ElementTree elements.
- Compose with raw ElementTree calls.
- Validate local numeric shape and finiteness.
- Do not attempt full SDFormat schema validation.
- Do not silently invent frames, axes, inertials, plugins, or sensor parameters.

## Recommended helper surface

Names may vary to match the current runtime package, but the helper surface should stay small.

```python
# XML basics
text(parent, tag, value, attrib=None)
fmt_float(value)
fmt_vector(values)

# Poses and axes
pose(parent, xyz=(0, 0, 0), rpy=(0, 0, 0), *, relative_to=None,
     rotation_format="euler_rpy", degrees=False)
quat_pose(parent, xyz=(0, 0, 0), quat_xyzw=(0, 0, 0, 1), *, relative_to=None)
axis(parent, xyz=(0, 0, 1), *, expressed_in=None)

# Document structure
sdf_root(version="1.12")
world(parent, name)
model(parent, name, *, static=None, pose=None)
frame(parent, name, *, attached_to=None, pose=None)
link(parent, name, *, pose=None, inertial=None)
joint(parent, name, joint_type, parent_link, child_link, *, pose=None,
      axis_xyz=None, axis_expressed_in=None, axis2_xyz=None, limits=None)

# Geometry
visual(parent, name, *, pose=None)
collision(parent, name, *, pose=None)
box(parent, size_xyz)
sphere(parent, radius)
cylinder(parent, radius, length)
capsule(parent, radius, length)
mesh(parent, uri, *, scale=None)

# Physics and metadata
inertial(parent, mass, inertia, *, pose=None)
sensor(parent, name, sensor_type, *, pose=None, topic=None, update_rate=None)
plugin(parent, name, filename, params=None)
include(parent, uri, *, name=None, pose=None)
```

## Numeric behavior

Helpers should reject:

- non-finite numbers;
- vectors with the wrong length;
- negative or zero primitive dimensions;
- zero joint axes;
- zero-mass inertials;
- zero-norm quaternions.

Helpers may warn, but should not silently fix:

- non-unit axes;
- non-normalized quaternions;