Rerun URDF ingestion

A URDF gives you a robot's geometry and its kinematic tree. Ingesting it means two API calls on one rerun.urdf.UrdfTree: stream the static model, then drive it with forward kinematics from joint states. The transforms it produces are derived, so they are a layer, never base (the URDF + joints (computed) row of the rerun-data-model table).

This skill is the UrdfTree API and the two judgment calls it cannot make for you: how your joint values map to URDF joints, and how the disconnected frames in the scene connect to one root. The stream/lens plumbing (LazyChunkStream, DeriveLens, Selector, writing and optimizing RRDs) is in rerun-chunk-processing; reach for it, do not re-derive it. Nothing below is tied to a data format: where your joint names, joint values, and calibration come from is yours to wire in.

Getting the URDF

Datasets rarely ship one, and the robot's own repo is not always the fastest route. In order:

• robot_descriptions.py, pip install robot_descriptions, then from robot_descriptions import ur5e_description; ur5e_description.URDF_PATH. It downloads and caches the upstream description and hands you a plain path with the meshes already next to it. Check its index first; it covers most of the table below.
• The vendor repo, when the description is newer than the package's pin or is not in it.
• MuJoCo Menagerie, MJCF, not URDF, so it needs conversion. Worth it only when nothing else exists.