CORE MODEL
Links and joints define the robot tree.
ROS documentation describes URDF as a file format for specifying robot geometry and organization. The URDF model is built around links and joints, with XML elements for visual, collision, inertial and joint properties.
STRENGTHS
Simple, inspectable and deeply integrated into ROS workflows.
Kinematic structure
Parent/child relationships and joint topology are explicit.
Geometry
Visual and collision geometry can be attached to robot links.
Inertials
Mass and inertia can be authored for physical links.
Joint limits
Joint type, axis, limits, dynamics and mimic relationships can be represented.
ROS ecosystem
URDF integrates naturally with robot_state_publisher and many ROS tools.
Human readability
XML structure is relatively direct to inspect and generate.
BOUNDARY
URDF is not trying to describe the whole embodied intelligence stack.
URDF does not natively answer every question an AI system may need about capabilities, provenance, lifecycle, governance or higher-level operational semantics. That is not a defect; it reflects the format’s primary responsibility.
OPENRGD IMPORT
URDF is treated as evidence, not as a complete robot constitution.
The OpenRGD importer preserves supported topology, inertials, limits, dynamics and mimic relationships. Missing values remain missing. It does not invent identity, safety policy, cognition, HAL bindings or actuation permission.
COMPARE
URDF and RGD solve different layers of the problem.
Links, joints, geometry, inertials, collision and joint constraints in a ROS-centric XML model.
Not a general scene-composition system or semantic embodiment graph.
USDComposable scene descriptionLarge hierarchical scenegraphs, references, variants, time-sampled data and physics schemas.
Not a robot-specific semantic capability or governance model by default.
SDFSimulation-oriented model and world descriptionRobots, environments, models, sensors, physics, lights, plugins and simulation context.
Not designed as a general AI embodiment-governance or provenance graph.
MJCFMuJoCo-native dynamic-system modelNested bodies, joints, actuators, tendons, sensors, defaults and simulator-native dynamic modeling.
Optimized for MuJoCo rather than cross-stack semantic embodiment.
RGDSemantic embodiment graphIdentity, physical evidence, operational constraints, capability semantics, provenance and lifecycle context.
Does not replace scene composition, a physics engine, middleware or a physical runtime.