AngleAxis and getunit error with Numpy 2.4

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Difficulty
2/5
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1-3 hours
Newbie friendliness
50/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
numpy, python
Domain
backend

Research direction

Reproduce the SO3.AngVec(theta=0, v=[0, 0, 1]) failure with NumPy 2.4, then inspect spatialmath/pose3d.py and spatialmath/base/transforms3d.py, including getunit and angvec2r. Done means the call no longer raises a TypeError under NumPy 2.4 and retains the expected identity rotation behavior.

Written by the indexing model from the issue text.

Description

Hi,

When calling SO3.AxisAngle in Python 3.11 with numpy 2.4, I get the error:

Python 3.11.11 | packaged by conda-forge | (main, Dec  5 2024, 08:47:03) [Clang 18.1.8 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> np.__version__
'2.4.0'
>>> from spatialmath import SO3
>>> SO3.AngVec(theta=0, v=[0, 0, 1])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/homebrew/Caskroom/miniconda/base/envs/vp_311/lib/python3.11/site-packages/spatialmath/pose3d.py", line 825, in AngVec
    return cls(smb.angvec2r(theta, v, unit=unit), check=False)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Caskroom/miniconda/base/envs/vp_311/lib/python3.11/site-packages/spatialmath/base/transforms3d.py", line 760, in angvec2r
    R = np.eye(3) + math.sin(θ) * sk + (1.0 - math.cos(θ)) * sk @ sk
                    ^^^^^^^^^^^
TypeError: only 0-dimensional arrays can be converted to Python scalars
>>>

However, with numpy 2.2, I get the expected behavior:

Python 3.11.11 | packaged by conda-forge | (main, Dec  5 2024, 08:47:03) [Clang 18.1.8 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> np.__version__
'2.2.6'
>>> from spatialmath import SO3
>>> SO3.AngVec(theta=0, v=[0, 0, 1])
SO3(array([[1., 0., 0.],
           [0., 1., 0.],
           [0., 0., 1.]]))

The error seems to stem from getunit, which when given a scalar now returns a 1-dimensional array instead of a 0-dimensional array. That then gets fed to math.cos, not np.cos, in angvec2r and the error occurs.

Thank you for all your work on this library,
JF

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