feat: add Arrow.FromTo(start, end) classmethod - #41
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Construct an Arrow spanning two points directly, without the caller having to compute length and pose by hand. Uses SE3.OA(reference, direction) to build the pose, not a delta rotation from a fixed reference (e.g. spatialmath's own SE3.RotatedVector) -- that approach has an antipodal singularity (direction exactly opposite the reference axis gives a zero-length cross product), confirmed live it currently returns identity instead of the correct 180 degree flip. OA sidesteps this entirely by directly specifying the target frame's axes. Companion fix proposed upstream: bdaiinstitute/spatialmath-python, branch fix/rotatedvector-antipodal. reference (the OA "orientation" vector) only needs to be non-parallel to direction -- irrelevant which valid one we pick, the arrow shaft is rotationally symmetric.
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Summary
Arrow.FromTo(start, end, **kwargs)classmethod -- constructs anArrowspanning two 3-vectors, computinglengthandposeautomatically instead of requiring the caller to do it by hand.
**kwargspass straight through to the constructor (color,radius,linewidth,head_length,head_radius, ...).SE3.OA(reference, direction)to build the pose, not a deltarotation from a fixed reference -- that class of approach (e.g.
spatialmath's own
SE3.RotatedVector) has an antipodal singularity:confirmed live that
SE3.RotatedVector([0,0,1], [0,0,-1])currentlyreturns identity instead of the correct 180° flip, since the cross
product used to find the rotation axis is zero right at that point.
SE3.OAsidesteps this entirely by directly specifying the targetframe's axes rather than computing a delta from Z. Companion fix
proposed upstream for the underlying bug:
bdaiinstitute/spatialmath-python, branch
fix/rotatedvector-antipodal(PR to follow).
reference(theOA"orientation" vector) only needs to benon-parallel to
direction-- which valid one gets picked isirrelevant, since the arrow shaft is rotationally symmetric.
ValueErrorifstart == end(direction, and therefore pose,would be undefined).
Test plan
pytest tests/-- 172 passedantipodal-to-world-Z directions (proving the antipodal case this PR is
specifically designed to avoid actually works); coincident-points
ValueError; kwargs pass-through