Correct theta values when drawing a non-circular arc by dstansby · Pull Request #8047 · matplotlib/matplotlib · GitHub

Fixes #8046. I'm not sure if this is the right place to do the correction, so a second opinion would be good. I've checked this works with a full range of angles.

add remove_text=True and style='default' to the decorator to get the new defaults + drop all of the text (which makes the test more stable).

This will need an entry in whats new or api changes. The paranoid case here is that users have worked around this bug and we are now silently changing things under them so it needs to be documented.

This looks like the correct place to do this to me. Ellipse is implemented by holding transforms to re-scale a circular path so pushing this down into Path.arc is not right and Ellipse is for full coverage so pushing this into the base-class is not right either.

Does anyone know why the documentation build is failing with:

/Users/dstansby/matplotlib/doc/examples/units/ellipse_with_units.rst:8: WARNING: Exception occurred in plotting ellipse_with_units
 from /Users/dstansby/matplotlib/doc/mpl_examples/units/ellipse_with_units.py:
Traceback (most recent call last):
  File "/Users/dstansby/matplotlib/lib/matplotlib/sphinxext/plot_directive.py", line 525, in run_code
    six.exec_(code, ns)
  File "<string>", line 55, in <module>
  File "/Users/dstansby/matplotlib/lib/matplotlib/patches.py", line 1565, in __init__
    theta1 = theta_stretch(theta1, width / height)
TypeError: unsupported operand type(s) for /: 'TaggedValue' and 'TaggedValue'

As far as I understand, it seems like “width” and “height” are cm instances from this script and that the class used under the hood (TaggedValue) does not implement the division operation.

Would anyone object to me just getting rid of http://matplotlib.org/examples/units/ellipse_with_units.html ? It doesn't seem to be showing any unique capabilities of units, and the 'comparison' just looks the same to me.

(and does it matter if my new code breaks drawing an ellipse with units?)

Yes and yes (although, it seems like the problem here is the exact unit implementation, not generally).

The unit support is an under-understood, but critical feature of mpl (JPL relies on it).

As far as I can tell:

The correct way to convert from units to a number is call self.convert_xunits(width)
However this is just returning width unchanged as units
This is because there is no axis when __init__ is called on Arc, so the units are returned unchanged

so all this means there's no way of converting units within the __init__ bit of Arc, so the conversion and angle correction needs to happen somewhere else.

That should fix it, I've moved the new calculation into the draw() method.

LGTM mostly. Just a small tweak to the test.

Could you also add the start of the arc as well? Start -> origin -> end should work.

enumerate(axs.flat)

Can you also add a full Ellipse patch with the same parameters but maybe half linewidth or alpha just to show that the arc is in a consistent place?

Thanks for the extra ideas for the test @QuLogic - once this has been reviewed I can squash everything down to a single commit.

Is there anything backend-specific here? Do we need the SVG/PDF files?

Oh yes, I forgot that those were optional. I don't think there's anything backend specific, shall I just have a .png image test?

Yes, I think we can drop the other ones and you can squash this.

Make arcs work with units Add api change not for elliptical notes Add background ellipse and extra line to test Remove pdf and svg tests for arc angles

Great, that should be all nicely squashed up now.

One more minor thing.

are -> arc

woops...

tacaswell added this to the 2.1 (next point release) milestone Feb 8, 2017

tacaswell reviewed Feb 8, 2017

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dstansby force-pushed the arc-theta branch from 00891c9 to 29470f9 Compare February 8, 2017 17:59

dstansby changed the title Correct theta values when drawing a non-circular ellipse Correct theta values when drawing a non-circular arc Feb 9, 2017

dstansby added the status: needs review label Feb 14, 2017

QuLogic reviewed Feb 23, 2017

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Correct theta values when drawing a non-circular ellipse

4bc50da

Make arcs work with units Add api change not for elliptical notes Add background ellipse and extra line to test Remove pdf and svg tests for arc angles

dstansby force-pushed the arc-theta branch from 785a8f9 to 4bc50da Compare March 2, 2017 21:48

QuLogic reviewed Mar 2, 2017

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Fix small typo in api change

0376d83

QuLogic approved these changes Mar 9, 2017

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QuLogic changed the title Correct theta values when drawing a non-circular arc [MRG+1] Correct theta values when drawing a non-circular arc Mar 9, 2017

NelleV approved these changes Mar 10, 2017

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NelleV merged commit beeba66 into matplotlib:master Mar 10, 2017

QuLogic changed the title [MRG+1] Correct theta values when drawing a non-circular arc Correct theta values when drawing a non-circular arc Mar 11, 2017

QuLogic removed the status: needs review label Mar 11, 2017

dstansby deleted the arc-theta branch April 2, 2017 16:44

ImportanceOfBeingErnest mentioned this pull request May 19, 2018

Arc patch ignoring theta1/theta2 when added to Axes via PatchCollection #11266

Closed

anntzer mentioned this pull request Jun 2, 2020

Arcs with large radii in small #17547

Closed

kiwifb mentioned this pull request Dec 25, 2017

Update matplotlib to 2.1.0 sagemath/sage#23696

Closed

+                      theta2 = i * 360 / 9
+                      theta1 = theta2 - 45
+                      ax.add_patch(patches.Arc(centre, w, h, theta1=theta1, theta2=theta2))
+                      # Straight line should intersect end of arc

+                  for i, ax in enumerate(np.ravel(axs)):
+                      theta2 = i * 360 / 9
+                      theta1 = theta2 - 45
+                      ax.add_patch(patches.Arc(centre, w, h, theta1=theta1, theta2=theta2))

		ax.plot([1, 2, 3])


		@image_comparison(baseline_images=['arc_angles'])

+                  centre = (0.2, 0.5)
+                  fig, axs = plt.subplots(3, 3)
+                  for i, ax in enumerate(np.ravel(axs)):

+              The `matplotlib.patches.Arc` patch is now correctly drawn between the given
+              angles.
+              Previously a circular are was drawn and then stretched into an ellipse,

Correct theta values when drawing a non-circular arc by dstansby · Pull Request #8047 · matplotlib/matplotlib · GitHub

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Correct theta values when drawing a non-circular arc - #8047

Correct theta values when drawing a non-circular arc#8047NelleV merged 2 commits intomatplotlib:mastermatplotlib/matplotlib:masterfrom dstansby:arc-thetadstansby/matplotlib:arc-thetaCopy head branch name to clipboard

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Correct theta values when drawing a non-circular arc#8047
NelleV merged 2 commits into
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dstansby:arc-theta

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