Allow forcing a fix axis scale ratio to maintain arrow lengths

[dabana]

Addresses issue #1187.

A new scaleratio parameter is added to the create_quiver function to allow forcing a fix scale ratio to the axis of the plot through the scaleratio option in the Layout. A distortion is introduced to the arrows length, angle and shape by having a scale ratio different than 1. In this pull request, this distortion is reversed by multiplying or dividing by scaleratio at key steps of the arrows construction.

[jonmmease]

Hi @dabana, I haven't reviewed/tested this in detail yet but at a high level this looks great! In the meantime, could you add a simple test to plotly/tests/test_optional/test_figure_factory/test_figure_factory.py? Just follow the pattern of the existing tests to make sure that the figure that's produced when scaleratio is set has the structure you expect.

Thanks for the great contribution!

[dabana]

It will be done.

[dabana]

There were no test class for the quiver plot, so I created it. But when trying out the tests with Nose:

nosetests -w plotly/tests/test_optional/test_figure_factory

I get the following import error:

ModuleNotFoundError: No module named 'retrying'

even though the retrying module is installed in my environment.

[jonmmease]

Thanks @dabana, this looks great! Thanks for the test, docstring, and example. I tried out several other examples and this makes the interpretation of the arrow lengths much more accurate.

Also, let me know if there's anything else you're interested in doing to improve create_quiver, it's so helpful to have contributors who also use the figure factory in their work 🙂

[dabana]

Great! This PR is a good first step toward issue #1187. I would like to make the choice of scaleratio a little more automatic for the user.