Events

Events#

In URBAN-SIM, events are simulation-time triggers that modify the environment state or robot behavior without terminating the episode. Events can occur on reset, periodically, or under specific conditions. They are defined using the EventTerm class and grouped under an EventCfg.

Taking COCO (a wheeled robot) as an example:

COCO Event Binding#

When robot_name = "coco", the following event config is registered:

@configclass
class EventCfg:
    reset_base = EventTerm(
        func=loc_mdp.reset_root_state_uniform,
        mode="reset",
        params={
            "pose_range": {
                "x": (0.3, 0.3),
                "y": (0.3, 0.3),
                "yaw": (0.0, 0.0)
            },
            "velocity_range": {
                "x": (0.0, 0.0),
                "y": (0.0, 0.0),
                "z": (0.0, 0.0),
                "roll": (0.0, 0.0),
                "pitch": (0.0, 0.0)
            },
        }
    )

This event is triggered in reset mode, meaning it will be applied at the beginning of each episode.

Event Term Parameters#

  • pose_range Specifies the randomization range for the robot’s base position and yaw (heading). In this case, it’s a fixed spawn at (x=0.3, y=0.3, yaw=0.0).

  • velocity_range Specifies the initial linear and angular velocity ranges. Setting all values to zero initializes the robot at rest.

Event Modes#

Each EventTerm has a mode, which determines when the event is triggered:

  • “reset”: Applied at the start of an episode

  • “step”: Applied during environment stepping (e.g., at intervals or conditions)

  • “manual”: Triggered via API calls or scripted logic

Defining Custom Events#

To define your own event:

  1. Create a Python function with signature: def my_event(env: ManagerBasedRLEnv, env_ids: Sequence[int], ...)

  2. Wrap it in an EventTerm(func=…, mode=…, params=…)

  3. Register it in your robot-specific EventCfg class.

Use cases include:

  • Randomizing initial state

  • Injecting wind or external forces

  • Resetting memory or trajectory buffers