Simulation & scenes

Sim wraps MuJoCo physics for a robot, and Scene builds the world around it. Together they’re the engine under every other feature.

`Sim`

Sim is the simulator handle for a robot. Build it, then run commands.

import cadenza_lab as cadenza

sim = cadenza.Sim(robot="go1", disturbance=0.3)
sim.run(["walk_forward", "turn_left", "sit"])
state = sim.get_state()      # dict: pose, velocity, contacts, …

Sim(robot="go1", xml_path=None, disturbance=None,
    disturbance_seed=None, scene=None)

Param	Description
`robot`	`"go1"` or `"g1"`.
`xml_path`	Override the MuJoCo model XML.
`disturbance`	Perturbation level (`0.0`–`1.0`), with optional `disturbance_seed`.
`scene`	A `Scene` to load (see below).

Methods

Method	Description
`run(commands, ...)`	Execute a command string or list. Retries up to `max_retries` (default 3).
`run_reactive(memory_fn, vla_fn, goal_fn, ...)`	Closed-loop control: at each step, `goal_fn`/`vla_fn` decide the next action from memory + observation.
`get_state()`	Return the current world state as a dict.

`Scene`

Scene builds a static world by adding primitives. Builder methods return the scene, so they chain. Pass it to Sim or GymAdapter.

scene = (
    cadenza.Scene()
      .add_box(position=[-1.3, 0.2, 0.08], size=[0.18, 0.18, 0.08])
      .add_slope(position=[-2.0, 0.0, 0.0], size=[1.0, 1.0, 0.1], angle_deg=15)
      .add_sphere(position=[-2.8, 0.0, 0.1], radius=0.12, rgba=[1, 0.2, 0.2, 1])
)
sim = cadenza.Sim(robot="go1", scene=scene)

Builder methods (all fixed=True, optional rgba):

Method	Signature
`add_box`	`add_box(position, size, *, fixed=True, rgba=None)`
`add_slope`	`add_slope(position, size, angle_deg, *, axis=(0,1,0), fixed=True, rgba=None)`
`add_sphere`	`add_sphere(position, radius, *, fixed=True, rgba=None)`
`snake`	`snake(*, start_x, step_x, count, snake_y=0.4, z=None, box_size=(0.07,0.07,0.07), rgba=...)`. A row of staggered boxes.
`snake_on_slope`	Same, laid over a slope.
`clear()`	Remove all added geometry.
`compile()`	Finalize the scene (called automatically when loaded).

Cadenza’s forward direction is −X. Positions and sizes are in MuJoCo world units (meters). size is half-extents for boxes/slopes.

`fixed` vs. dynamic objects

fixed=True (default) welds the object to the world. fixed=False wraps it in a body with a free joint, so it falls under gravity and the robot can shove it.

scene.add_box(position=[-1.0, 0, 0.1], size=[0.1, 0.1, 0.1], fixed=False)  # kickable

State & sensing

Sim.get_state() returns a dict the closed-loop helpers and modalities read from:

Key	Meaning
`pos`, `yaw`, `roll`, `pitch`, `body_height`	Base pose.
`foot_contacts`	Per-foot ground contact (0/1).
`terrain_ahead`	Downward raycasts: `max_step_up`, ground heights ahead.
`obstacles_ahead`	Forward raycasts: nearest hit left/center/right (`min_m`, `side`).

Demo: build a world and read it back

"""demo_scene.py: compile a scene, read terrain/obstacle sensing (headless)."""
import cadenza_lab as cadenza

scene = (
    cadenza.Scene()
      .add_box(position=[-1.3, 0.2, 0.08], size=[0.18, 0.18, 0.08])
      .add_slope(position=[-2.4, 0.0, 0.0], size=[0.8, 0.6, 0.05], angle_deg=12)
      .add_sphere(position=[-2.9, -0.3, 0.12], radius=0.12, rgba=[1, 0.2, 0.2, 1])
)

sim = cadenza.Sim(robot="go1", scene=scene, disturbance=0.2, disturbance_seed=0)
state = sim.get_state()
print("body height:", round(state["body_height"], 3))
print("obstacle ahead (min m):", state["obstacles_ahead"]["min_m"])
print("max step-up ahead:", round(state["terrain_ahead"]["max_step_up"], 3))

# To watch it instead of inspecting it (opens a viewer window):
# cadenza.view(robot="go1", scene=scene)

python demo_scene.py

Get started

Features

Tutorial

`Sim`

`Scene`

`fixed` vs. dynamic objects

State & sensing

Demo: build a world and read it back

​Sim

​Scene

​fixed vs. dynamic objects

​State & sensing

​Demo: build a world and read it back

`Sim`

`Scene`

`fixed` vs. dynamic objects

State & sensing

Demo: build a world and read it back