[petercorke]

Fixes #843.

The line of sight of Robot.vision_collision_damper was oriented with arccos of the dot product and the cross product of the two vectors. For a camera directly above or below the target the vectors are parallel or antiparallel, the cross product is zero, and the rotation is about no axis. Today that gives the identity, which is wrong for the antiparallel case (a camera below the target draws the line of sight the wrong way), and once SpatialMath rejects a zero axis (rai-opensource/spatialmath-python#267) it would be a ValueError. arccos also gives nan when the dot product is 1.0000000000000002.

The orientation is now SE3(SO3.RotatedVector(a, b)), in a small module-level function, _rotation_between_vectors, so it can be tested. SO3.RotatedVector is in the released SpatialMath 1.1.18, so no change to the pin.

Tests: tests/test_vision_collision_orientation.py (20 cases: parallel, parallel to rounding, antiparallel, generic and random vectors, a camera above and below a target, and no warnings). Each checks that the rotation is proper and takes the direction of a to that of b. With the old computation in place, 10 of them fail.

Checked against both SpatialMath behaviours, running the function from this branch in two throwaway virtual environments:

• released 1.1.18: the old code was silently wrong for antiparallel vectors, the new code is correct in every case
• the branch of angvec2r: reject a zero axis for a non-zero angle rai-opensource/spatialmath-python#267: the old code raised ValueError for antiparallel and for parallel-to-rounding vectors, the new code is correct in every case

Also 500 random pairs, with no failures in either. The test suite here runs against the #267 behaviour, since the SpatialMath checkout in this environment is on that branch. No change to behaviour other than for these degenerate cases.

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[codacy-production]

Not up to standards ⛔

🔴 Issues 2 high

Alerts:
⚠ 2 issues (≤ 0 issues of at least minor severity)

Results:
2 new issues

Category	Results
Security	2 high

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🟢 Metrics 11 complexity · 0 duplication

Metric	Results
Complexity	11
Duplication	0

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (f0e22c0) to head (8557525).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/roboticstoolbox/robot/Robot.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #845   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        146     146           
  Lines      16836   16838    +2     
=====================================
- Misses     16836   16838    +2     

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