Assets

Assets are the objects and backgrounds that make up a scene. Arena ships with a set of assets ready to use by name, and new assets can be added by registering them in the asset library.

background = asset_registry.get_asset_by_name("kitchen")()
cracker_box = asset_registry.get_asset_by_name("cracker_box")()

Registering a new asset

To add a new object, subclass LibraryObject, provide the USD path and object type, and decorate it with @register_asset:

@register_asset
class MyObject(LibraryObject):
    name = "my_object"
    tags = ["object", "graspable"]
    usd_path = "path/to/my_object.usd"
    object_type = ObjectType.RIGID

Once registered, the object is available in the registry like any other asset:

obj = asset_registry.get_asset_by_name("my_object")()

Assets can also be tagged to make them discoverable by category:

# All graspable objects
objects = asset_registry.get_assets_by_tag("graspable")

# A random graspable object
obj = asset_registry.get_random_asset_by_tag("graspable")()

Useful tags include "graspable", "openable", "pressable", and "background". Assets can have multiple tags — for example, a fruit is tagged both "graspable" and "food".

Object types

Every asset has an object type that determines how it is simulated:

• RIGID — a single rigid body (boxes, bottles, tools, furniture).

• ARTICULATION — a multi-body object with joints (robots, doors, drawers, appliances).

• BASE — no physics; used for static backgrounds and markers.

Backgrounds

Backgrounds are registered as BASE assets, but their composed USDs may contain dynamic rigid bodies and articulations whose states can change as they interact with the robot or other objects. Set reset_nested_physics=True on a Background to reset these nested physics roots.

Arena registers the roots as private Isaac Lab reset views. After simulation and RTX initialization, Arena creates the views and records one environment-local pose and joint configuration. On each episode reset, Arena applies those values to the resetting environments and zeros all root and joint velocities. The private views are not exposed through the Isaac Lab scene entity registries.

Arena discovers nested roots through the composed USD physics APIs.

Included:

• Standalone rigid bodies.

• Articulation roots, which own their links and joints.

Excluded:

• BASE and collision-only prims.

• Rigid and articulation roots owned by matching ObjectReference entries.

• Articulation links, which cannot own reset state independently.

• Authored roots without a live physics backend object after composition.

BASE object references remain observational and do not transfer reset ownership away from the background.

Instanceable subtrees that contribute dynamic physics are materialized at spawn time because physics views cannot control dynamic instance proxies.

Object references

A background asset like a kitchen is a single USD file containing many prims: countertops, shelves, drawers, and so on. To use one of these internal prims as a destination or interaction target (e.g. “place the object on the counter”), you use an ObjectReference.

kitchen = asset_registry.get_asset_by_name("kitchen")()

counter = ObjectReference(
    name="kitchen_counter",
    prim_path="{ENV_REGEX_NS}/kitchen/counter_right_main_group/top_geometry",
    parent_asset=kitchen,
)

task = PickAndPlaceTask(
    pick_up_object=cracker_box,
    destination_location=counter,
    background_scene=kitchen,
)

The parent_asset tells the environment which spawned USD the prim path belongs to. The prim path uses {ENV_REGEX_NS} so it resolves correctly across parallel environments.

Rigid object sets

To fill one scene role with different rigid objects across parallel environments, wrap the candidates in a RigidObjectSet. See Rigid Object Sets for motivation, usage, and limitations.