Mujoco model learning record

---

body

1 worldbody special body, As the of the world frame

This element is used to construct the kinematic tree via nesting. The element worldbody is used for the top-level body, while the element body is used for all other bodies. The top-level body is a restricted type of body: it cannot have child elements inertial and joint, and also cannot have any attributes. It corresponds to the origin of the world frame, within which the rest of the kinematic tree is defined. Its body name is automatically defined as “world”.

Cannot configure properties

2 body Realization object of robot connecting rod and joint

2.1 name: string, optional

Name of the body.

mesh and auctor Need to pass through name Associated with a connecting rod or joint

2.2 pos: real(3), optional

The 3D position of the body frame, in local or global coordinates as determined by the coordinate attribute of compiler. Recall the earlier discussion of local and global coordinates in Coordinate frames. In local coordinates, if the body position is left undefined it defaults to (0,0,0). In global coordinates, an undefined body position is inferred by the compiler through the following steps:

1. If the inertial frame is not defined via the inertial element, it is inferred from the geoms attached to the body. If there are no geoms, the inertial frame remains undefined. This step is applied in both local and global coordinates.

2. If both the body frame and the inertial frame are undefined, a compile error is generated.

3. If one of these two frames is defined and the other is not, the defined one is copied into the undefined one. At this point both frames are defined, in global coordinates.

4. The inertial frame as well as all elements defined in the body are converted to local coordinates, relative to the body frame.

Note that whether a frame is defined or not depends on its pos attribute, which is in the special undefined state by default. Orientation cannot be used to make this determination because it has an internal default (the unit quaternion).

2.3 geom body Appearance properties

This element creates a geom, and attaches it rigidly to the body within which the geom is defined. Multiple geoms can be attached to the same body. At runtime they determine the appearance and collision properties of the body. At compile time they can also determine the inertial properties of the body, depending on the presence of the inertial element and the setting of the inertiafromgeom attribute of compiler. This is done by summing the masses and inertias of all geoms attached to the body with geom group in the range specified by the inertiagrouprange attribute of compiler. The geom masses and inertias are computed using the geom shape, a specified density or a geom mass which implies a density, and the assumption of uniform density.
Geoms are not strictly required for physics simulation. One can create and simulate a model that only has bodies and joints. Such a model can even be visualized, using equivalent inertia boxes to represent bodies. Only contact forces would be missing from such a simulation. We do not recommend using such models, but knowing that this is possible helps clarify the role of bodies and geoms in MuJoCo.

2.3.1 type: [plane, hfield, sphere, capsule, ellipsoid, cylinder, box, mesh], “sphere”

---

contact (*)