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Fix default theta tick locations for non-full-circle polar plots. #20012

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Apr 20, 2021
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Fix default theta tick locations for non-full-circle polar plots. #20012

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5 changes: 5 additions & 0 deletions doc/api/next_api_changes/behavior/20012-AL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
Default theta tick locations for non-full-circle polar plots have changed
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For polar plots that don't cover a full circle, the default theta tick
locations are now at multiples of 10°, 15°, 30°, 45°, 90°, rather than using
values that mostly make sense for linear plots (20°, 25°, etc.).
4 changes: 4 additions & 0 deletions lib/matplotlib/projections/polar.py
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Expand Up @@ -393,6 +393,10 @@ def _set_scale(self, value, **kwargs):
raise NotImplementedError(
"The xscale cannot be set on a polar plot")
super()._set_scale(value, **kwargs)
# LinearScale.set_default_locators_and_formatters just set the major
# locator to be an AutoLocator, so we customize it here to have ticks
# at sensible degree multiples.
self.get_major_locator().set_params(steps=[1, 1.5, 3, 4.5, 9, 10])
self._wrap_locator_formatter()

def _copy_tick_props(self, src, dest):
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16 changes: 16 additions & 0 deletions lib/matplotlib/tests/test_polar.py
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Expand Up @@ -249,6 +249,8 @@ def test_polar_theta_limits():
direction=DIRECTIONS[i % len(DIRECTIONS)],
rotation='auto')
ax.yaxis.set_tick_params(label2On=True, rotation='auto')
ax.xaxis.get_major_locator().base.set_params( # backcompat
steps=[1, 2, 2.5, 5, 10])


@check_figures_equal(extensions=["png"])
Expand Down Expand Up @@ -357,3 +359,17 @@ def test_thetalim_args():
assert tuple(np.radians((ax.get_thetamin(), ax.get_thetamax()))) == (0, 1)
ax.set_thetalim((2, 3))
assert tuple(np.radians((ax.get_thetamin(), ax.get_thetamax()))) == (2, 3)


def test_default_thetalocator():
# Ideally we would check AAAABBC, but the smallest axes currently puts a
# single tick at 150° because MaxNLocator doesn't have a way to accept 15°
# while rejecting 150°.
fig, axs = plt.subplot_mosaic(
"AAAABB.", subplot_kw={"projection": "polar"})
for ax in axs.values():
ax.set_thetalim(0, np.pi)
for ax in axs.values():
ticklocs = np.degrees(ax.xaxis.get_majorticklocs()).tolist()
assert pytest.approx(90) in ticklocs
assert pytest.approx(100) not in ticklocs