🔷 Geometry#

Geometry determines the appearance and collision properties of objects in the scene. Geometries can be added under <body> or <worldbody>, or used to configure default-related properties. MJCF Geometry Configurable Attributes

Geometry Types#

Currently supported geometry types are as follows:

Type	Description
Plane (`plane`)	Infinite plane dividing the entire scene, can only be configured under `worldbody` or a static `body`. In the plane’s local coordinate system, the Z-axis is the normal direction. The region below the plane (−Z direction) is the collision area. The first two values of the `size` parameter are only for visualization and do not affect collision volume.
Height field (`hfield`)	Requires referencing an asset under the corresponding `hfield` tag. No need to configure the `size` attribute. For an example, see `examples/assets/hfield.xml`.
Sphere (`sphere`)	The `size` attribute has only 1 value, defining the radius of the sphere.
Capsule (`capsule`)	Can be regarded as composed of two hemispheres and a cylinder. The `size` consists of the radius of the hemispheres and the half-height of the cylinder.
Cylinder (`cylinder`)	The `size` consists of the radius of the circle and the half-height of the cylinder.
Box (`box`)	The `size` consists of the half-lengths along the X, Y, and Z directions.
Mesh (`mesh`)	Requires referencing an asset under the corresponding `mesh` tag. No need to configure the `size` attribute. For an example, see `examples/assets/boston_dynamics_spot/spot.xml`.

Main Interfaces#

In MotrixSim, you can access Geom objects in the following ways:

model.num_geoms: Get the number of Geoms in the current world.
model.geoms: Get all Geom objects in the current world.
model.get_geom(key): Get a specific Geom object by name or index.

Once you obtain a Geom object, you can read information such as its position, orientation, velocity, etc. For details, please refer to the Geom API.

Example#

You can run a simple example of Geom API usage with:

uv run examples/physics/geom.py

See the source code at examples/physics/geom.py。

Height Fields (HField)