Implementation:Haosulab ManiSkill MujocoObject

Knowledge Sources	Haosulab_ManiSkill
Domains	Robotics, Simulation, Scene_Building
Last Updated	2026-02-15 08:00 GMT

Overview

Concrete tool providing the base MujocoObject class that mimics robosuite's MujocoXMLObject for loading and managing MJCF-based objects in ManiSkill's SAPIEN simulation.

Description

The MujocoObject class serves as the foundational object representation for RoboCasa fixtures, bridging between MJCF XML descriptions and SAPIEN's actor/articulation system. It is adapted from robosuite's MujocoXMLObject class.

Key functionality:

MJCF Loading -- Uses SAPIEN's MJCF loader to parse XML model files from the RoboCasa asset directory. Visual group 1 is used for rendering (group 0 is for collisions). The loader produces either an actor_builder or articulation_builder.
Pose management -- Tracks position (pos), quaternion (quat), and provides set_pos(), set_euler(), and rotation property (rot).
Scaling -- set_scale(scale) applies uniform or per-axis scaling to all visual records, collision records, joint poses, and bounds sites. Handles cylinder/capsule shapes differently from box shapes (scaling radius and length vs. scale vector).
Bounding sites -- Parses exterior and interior bounding box sites (ext_p0/px/py/pz, int_p0/px/py/pz) from the XML for spatial calculations.
Bounding box -- get_bbox_points() computes 8 bounding box corner points with optional translation and rotation.
Offset properties -- bottom_offset, top_offset, and horizontal_radius read from MJCF sites with scale applied.

A helper function site_pos(elem) extracts position from an XML element's "pos" attribute.

Usage

Base class for Fixture, CabinetPanel, Handle, and other RoboCasa components. Not typically instantiated directly.

Code Reference

Source Location

Repository: Haosulab_ManiSkill
File: mani_skill/utils/scene_builder/robocasa/fixtures/mujoco_object.py

Signature

def site_pos(elem) -> np.ndarray: ...

class MujocoObject:
    def __init__(self, scene: ManiSkillScene, xml: Optional[str], name: str,
                 pos: np.ndarray = None, scale: float = 1): ...
    @property
    def rot(self) -> float: ...
    def set_pos(self, pos): ...
    def set_euler(self, euler): ...
    def set_scale(self, scale): ...
    def get_bbox_points(self, trans=None, rot=None) -> list: ...
    @property
    def bottom_offset(self) -> np.ndarray: ...
    @property
    def top_offset(self) -> np.ndarray: ...
    @property
    def horizontal_radius(self) -> np.ndarray: ...

Import

from mani_skill.utils.scene_builder.robocasa.fixtures.mujoco_object import MujocoObject

I/O Contract

Method/Property	Input	Output	Description
`__init__`	`scene, xml, name, pos, scale`	MujocoObject instance	Loads MJCF, creates actor/articulation builder
`set_scale`	`scale: float or array`	None	Applies scale to visuals, collisions, joints, sites
`get_bbox_points`	`trans, rot` (optional)	`list` of 8 3D points	Computes 8-corner bounding box
`bottom_offset`	--	`np.ndarray`	Bottom site position (scaled)
`top_offset`	--	`np.ndarray`	Top site position (scaled)

Usage Examples

# MujocoObject is typically used as a base class
class MyFixture(MujocoObject):
    def __init__(self, scene, xml, name, **kwargs):
        super().__init__(scene, xml, name, **kwargs)
        # Access bounding information
        bbox = self.get_bbox_points()
        print(f"Bottom: {self.bottom_offset}")
        print(f"Top: {self.top_offset}")

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