Inverse pole density distribution 2

[harripj]

Description of the change

This is the new PR for #355 after that PR was pre-maturely merged.

Previous PR description below

Following on from #340, it is often useful to view the pole density function (PDF) in the fundamental sector of the crystal symmetry, ie. the inverse pole density function (IPDF).

To implement this, the StereographicPlot.pole_density_function() has been updated to work with the subclass InverseStereographicPlot. When calculating PDF, the axes are checked as to whether they have a _symmetry attribute, ie. IPF, and if so the calculated PDF is folded back into the fundamental sector.

At the moment there are some issues with the implementation, regarding aliasing (during folding procedure) and the axes limits (which I may be due to QuadMesh, see plot size below), see the examples below. Grateful for any suggestions, feedback, or help regarding this!

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

Minimal example of the bug fix or new feature

from matplotlib import pyplot as plt
from orix import plot
from orix.quaternion import symmetry
from orix.vector import Vector3d

fig = plt.figure(figsize=(15, 5))

ax0 = fig.add_subplot(131, projection='stereographic')
ax1 = fig.add_subplot(132, projection='ipf', symmetry=symmetry.Oh)
ax2 = fig.add_subplot(133, projection='ipf', symmetry=symmetry.C6)

v = Vector3d([(-2, 0, 1), [2, 2, 1], [1, 1, 2], [0.5, -0.3, 0.2]]).unit

ax0.pole_density_function(v)
ax1.pole_density_function(v, resolution=0.25)
ax2.pole_density_function(v, resolution=0.25)

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• Contributor(s) are listed correctly in __credits__ in orix/__init__.py and in
  .zenodo.json.

[hakonanes]

This is a very nice PR with robust testing and neat reusing of one function to provide the inverse pole density function calculations to three classes Vector3d, StereographicPlot and InverseStereographicPlot.

Should the IPDF be used in a user guide tutorial (notebook)? That can be left for another PR, of course, but should perhaps be done before the next release.

I've made several suggestions for changes, mostly in the docstrings and slight changes to code. Otherwise, I think this is good to go.

[hakonanes]

I've resolved all but one insignificant comment on comments... Feel free to ping me when you wan't a second review!

[harripj]

I've resolved all but one insignificant comment on comments... Feel free to ping me when you wan't a second review!

Thanks, I had missed a couple abbreviations in the inline comments- this should be good for a second look!

[hakonanes]

Found a couple of things that should be changed, sorry for missing these in the first review.

[hakonanes]

This looks very good to me! Will let you merge once all checks pass and you're happy.

[harripj]

Thanks for the review @hakonanes, I am happy with this. I will just wait to see if @pc494 has any comments on #351, as you commented, before merging.

[pc494]

Apologies for the delay. I think measure is a fine name for this sort of functionality. Feel free to merge @hakonanes