NATIVE MODEL
MJCF maps directly onto MuJoCo’s modeling system.
MuJoCo documents MJCF as its native model format. The main kinematic structure is represented by nested body elements under worldbody , while joints create degrees of freedom between bodies instead of connecting separately declared links.
RICH DYNAMICS
The format exposes simulator-native modeling concepts.
Bodies + joints
Nested bodies form the kinematic tree and may contain multiple joints.
Actuators
Actuation models and controller-related parameters are native parts of MJCF.
Sensors
Simulation-oriented sensor definitions are part of the model language.
Tendons
Tendon routing and constraints can be represented directly.
Defaults
Reusable defaults reduce repetition across complex models.
Compiler
High-level MJCF is compiled into MuJoCo’s lower-level mjModel representation.
URDF IMPORT
MuJoCo supports URDF, but URDF represents a subset of what MJCF can express.
MuJoCo can load URDF models and provides MuJoCo-specific URDF extensions. Its documentation explicitly notes that URDF can represent only a subset of the model elements available in MuJoCo and recommends converting to MJCF when users need the full feature set.
OPENRGD POSITION
MJCF is a simulator-native model; RGD is semantic embodiment context.
OpenRGD should not imitate MJCF’s simulator responsibilities. A future adapter can treat MJCF as physical/simulation evidence, while RGD remains responsible for provenance, semantic identity, capabilities, operational context and lifecycle.
COMPARE
Five formats, five centers of gravity.
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.