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Stop link transform drift on repeated SetDOFValues with bodyTransform #1555

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Stop link transform drift on repeated SetDOFValues with bodyTransform #1555

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fix: stop link transform drift on repeated SetDOFValues with bodyTran…
Puttichai May 26, 2026
d5cbda0
Merge remote-tracking branch 'origin/production' into fix_link_drift_…
Puttichai Jun 15, 2026
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chore: improve comment
Puttichai Jun 15, 2026
49008e7
Merge remote-tracking branch 'origin/production' into fix_link_drift_…
Puttichai Jun 22, 2026
bf9626c
Merge remote-tracking branch 'origin/production' into fix_link_drift_…
Puttichai Jul 14, 2026
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19 changes: 10 additions & 9 deletions src/libopenrave/kinbody.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2193,15 +2193,16 @@ void KinBody::SetDOFValues(const std::vector<dReal>& vJointValues, const Transfo
if( _veclinks.size() == 0 ) {
return;
}
Transform baseLinkTransform = bodyTransform * _baseLinkInBodyTransform;
Transform tbase = baseLinkTransform*_veclinks.at(0)->GetTransform().inverse();
_veclinks.at(0)->SetTransform(baseLinkTransform);

// apply the relative transformation to all links!! (needed for passive joints)
for(size_t i = 1; i < _veclinks.size(); ++i) {
_veclinks[i]->SetTransform(tbase*_veclinks[i]->GetTransform());
}
SetDOFValues(vJointValues,checklimits);
// Reuse the SetTransform loop instead of setting link[0] directly and propagating a relative
// transform to link[i>0]. The direct set lets the floating-point error in
// baseLinkTransform * link[0].GetTransform().inverse() be the same on every call, so the
// non-root link transforms drift by that same epsilon each call and accumulate. Applying
// tapply to every link (including link[0]) lets link[0] absorb the same epsilon, so the next
// call's tapply is approximately (identity - epsilon) and the drift cancels rather than
// compounds. For DOF>0 bodies the subsequent SetDOFValues recomputes link transforms via FK
// and overwrites this loop's output, so the change only affects 0-DOF multi-link bodies.

@kanbouchou kanbouchou Jun 15, 2026

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// For DOF>0 bodies the subsequent SetDOFValues recomputes link transforms via FK and overwrites this loop's output, so the change only affects 0-DOF multi-link bodies.

I think "the change" may make sense in the PR context where we are seeing old and new code side-by-side. However, once merged into production, this comment may not be clear what "the cahnge" refers to. Can you rephrase to something which makes sense without knowing the old code?

@Puttichai Puttichai Jun 15, 2026

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Thank you for checking. I updated the comment.

_SetTransformNoPostProcess(bodyTransform);
SetDOFValues(vJointValues, checklimits);
}

void KinBody::SetDOFValues(const std::vector<dReal>& vJointValues, uint32_t checklimits, const std::vector<int>& dofindices)
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