Add helper utilities for raw surface-to-surface distance computations ( geom_distance_utils.py ) #2689
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… (geom_distance_utils.py) MuJoCo’s mj_geomDistance returns a signed distance with geom margins already subtracted, which often confuses users.\n\nThis commit adds python/geom_distance_utils.py providing:\n * sdf(): thin wrapper that allocates the fromto buffer for mj_geomDistance.\n * raw_gap(): returns the raw surface-to-surface gap by adding the two geom margins back.\n * batch_raw_gap(): vectorised helper for many geom pairs that avoids per-call allocations.\n\nIncludes CLI example usage when run as a script. No existing code is modified.
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Motivation
MuJoCo’s mj_geomDistance function returns a signed distance with each geom's geom_margin already subtracted, which can result in negative values even when objects are not in contact. This behavior frequently confuses users and requires boilerplate code to handle correctly. Additionally, the function incurs per-call buffer allocation overhead, which can be costly in performance-critical applications.
Key Additions
New module:
python/geom_distance_utils.pysdf(model, data, gid1, gid2, ...)– A thin wrapper around mj_geomDistance that returns the raw signed distance while managing buffer allocation internally.
raw_gap(model, data, gid1, gid2, ...)– Returns the actual surface-to-surface gap by re-adding both geoms' margins to the signed distance.
batch_raw_gap(model, data, gid_pairs, ...)– A vectorized, memory-efficient method for computing multiple raw gaps, ideal for performance-critical loops.
Self-contained CLI Example
– Run python
geom_distance_utils.py <model.xml>to see the utility in action.Documentation & Comments
– Includes clear docstrings and inline comments to explain MuJoCo's margin behavior and how this module resolves common pitfalls.
Benefits
Removes ambiguity around MuJoCo’s margin-subtracted signed distances.
Reduces overhead by reusing buffers and avoiding repeated allocations.
Simplifies research scripts by avoiding manual margin bookkeeping.
Completely additive: no changes to existing files or build systems required.