Heuristic:ARISE Initiative Robosuite XML Reset Method Tradeoff

Knowledge Sources	DataCollectionWrapper XML Bug
Domains	Data_Collection, Debugging, Robotics_Simulation
Last Updated	2026-02-15 07:00 GMT

Overview

The `DataCollectionWrapper` offers two XML serialization methods for saving environment state; `env.model.get_xml()` can trigger rare mesh inertia errors while `sim.model.get_xml()` avoids these but causes subtle physics changes like doors being harder to close.

Description

When collecting demonstration data, the `DataCollectionWrapper` saves the complete environment state at the start of each episode for deterministic replay. This requires serializing the MuJoCo model to XML. There are two methods available: `self.env.model.get_xml()` (the robosuite model's XML) and `self.env.sim.model.get_xml()` (MuJoCo's internal compiled model XML). These produce subtly different XML, and each has different failure modes. The wrapper exposes a `use_env_xml_for_reset` flag to choose between them.

Usage

Use this heuristic when:

Setting up the `DataCollectionWrapper` for demonstration collection
Encountering `ValueError: Error: eigenvalues of mesh inertia violate A + B >= C` during data collection
Noticing that doors or articulated objects behave differently during demonstration playback vs. live interaction
Debugging deterministic replay failures

The Insight (Rule of Thumb)

Action: If you encounter the mesh inertia eigenvalue error, set `use_env_xml_for_reset=False` to use `sim.model.get_xml()` instead.
Action: If physics fidelity during replay is critical (e.g., door closing behavior must match), use `use_env_xml_for_reset=True` (default) and handle the rare inertia errors by restarting the affected episode.
Trade-off: `env.model.get_xml()` preserves original model fidelity but can trigger rare mesh inertia validation errors. `sim.model.get_xml()` never triggers these errors but introduces subtle physics differences because MuJoCo's internal model has been processed/compiled.
Context: The physics differences are most noticeable in articulated objects with constraints (e.g., doors with hinges become harder to close).

Reasoning

The two XML methods produce different outputs because:

`env.model.get_xml()` returns the original MJCF XML that was used to construct the robosuite model. This is the "source" XML before MuJoCo compilation. It preserves the exact parameter values specified by the user/model but may contain configurations that fail MuJoCo's internal validation during re-loading (specifically, mesh inertia eigenvalue constraints).

`sim.model.get_xml()` returns MuJoCo's serialized representation of the compiled model. MuJoCo may have adjusted parameters during compilation (e.g., inertia values, constraint parameters), so this XML is guaranteed to load without validation errors. However, these adjustments mean the re-loaded model may behave slightly differently from the original.

The deterministic replay trick also requires saving the flat simulation state and replaying with `reset_from_xml_string()` followed by `set_state_from_flattened()`. Both the XML and state must be consistent for replay to work correctly.

Code evidence from `robosuite/wrappers/data_collection_wrapper.py:75-84`:

# NOTE: was originally set to self.env.model.get_xml()
# That was causing the following issue in rare cases:
# ValueError: Error: eigenvalues of mesh inertia violate A + B >= C
# then, switched to self.env.sim.model.get_xml() which does not create this issue
# however, that leads to subtle changes in the physics, such as fixture doors being harder to close
# so, in order to address both issues, added an flag to choose between the two methods
if self.use_env_xml_for_reset:
    self._current_task_instance_xml = self.env.model.get_xml()
else:
    self._current_task_instance_xml = self.env.sim.model.get_xml()

Code evidence from `robosuite/wrappers/data_collection_wrapper.py:87-93`:

# trick for ensuring that we can play MuJoCo demonstrations back
# deterministically by using the recorded actions open loop
self.env.set_ep_meta(self.env.get_ep_meta())
self.env.reset_from_xml_string(self._current_task_instance_xml)
self.env.sim.reset()
self.env.sim.set_state_from_flattened(self._current_task_instance_state)
self.env.sim.forward()

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