beachball.py

# -*- coding: utf-8 -*-
from __future__ import (absolute_import, division, print_function,
                        unicode_literals)

import matplotlib.pyplot as plt
import matplotlib.collections as mcollections
import matplotlib.patches as mpatches
import matplotlib.transforms as mtransforms


def beach(axes):
    xy = (0, 0)
    paths = [
        mpatches.Ellipse(xy, width=400, height=400),
        mpatches.Ellipse(xy, width=300, height=300),
        mpatches.Ellipse(xy, width=200, height=200),
    ]
    colors = ['b', 'w', 'g']

    col = mcollections.PatchCollection(paths, match_original=False)
    col.set_facecolors(colors)

    # Use the given axes to maintain the aspect ratio of beachballs on figure
    # resize.
    # This is what holds the aspect ratio (but breaks the positioning)
    col.set_transform(mtransforms.IdentityTransform())
    # Next is a dirty hack to fix the positioning:
    # 1. Need to bring the all patches to the origin (0, 0).
    for p in col._paths:
        p.vertices -= xy
    # 2. Then use the offset property of the collection to position the
    #    patches
    col.set_offsets(xy)
    col._transOffset = axes.transData

    col.set_edgecolor('k')

    return col


fig = plt.figure()
ax = fig.add_subplot(111)
ax.add_collection(beach(axes=ax))
ax.axis([-10000, 10000, -100, 100])
fig.savefig('bb_aspect_x.png')