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pdhall99 opened this issue Feb 8, 2017 · 3 comments
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Arc patch with starting and ending angle #8046

pdhall99 opened this issue Feb 8, 2017 · 3 comments
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@dstansby
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v2.1

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@pdhall99
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pdhall99 commented Feb 8, 2017 •
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Bug report

Bug summary

  • Arc patch does not behave as expected when drawing elliptical arcs between two angles specified by theta1 and theta2.

Code for reproduction

import matplotlib.pyplot as plt
from matplotlib.patches import Arc

# Ellipse parameters
R = 1.0
x, y = 0.0, 0.0
a, b = 2.0*R, R

# Figure setup
fig_width, fig_height = 3.30, 3.30
fig = plt.figure(figsize=(fig_width, fig_height), frameon=False)
ax = fig.add_axes([0.0, 0.0, 1.0, 1.0], aspect='equal')
ax.set_axis_off()
ax.set_xlim(-R*1.05, R*1.05)
ax.set_ylim(-R*1.05, R*1.05)
# Axes
ax.axhline(0.0)
ax.axvline(0.0)
# 45 degree line
ax.plot([0.0, 1.0], [0.0, 1.0], 'k--')
# Arcs
ax.add_patch(Arc((x, y), a, b, 
                 theta1=0.0, theta2=360.0, edgecolor='k'))
ax.add_patch(Arc((x, y), a, b,
                 theta1=0.0, theta2=45.0, edgecolor='r', lw=1.5))
fig.savefig('Arc_patch_bug.png')

Actual outcome

arc_patch_bug

Expected outcome

  • Red elliptical arc between the x-axis (0 degrees) and the dashed line (45 degrees), following the black ellipse.

Matplotlib version

  • Matplotlib 2.0.0, Python 2.7.13, OSX
  • Installed with MacPorts
@dstansby
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dstansby commented Feb 8, 2017

I'm trying to run your example, but you haven't specified angle_deg anywhere in the code (so adding the patches fails).

@dstansby
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dstansby commented Feb 8, 2017

I can reproduce this using a stripped down example:

import matplotlib.pyplot as plt
from matplotlib.patches import Arc

# Ellipse parameters
R = 1
x, y = 0, 0
a, b = 2 * R, R

# Figure setup
fig, ax = plt.subplots()
ax.set_xlim(-R * 1.05, R * 1.05)
ax.set_ylim(-R * 1.05, R * 1.05)
# 45 degree line
ax.plot([0, 1], [0, 1])
# Arcs
ax.add_patch(Arc((x, y), a, b,
                 theta1=0, theta2=360, edgecolor='k'))
ax.add_patch(Arc((x, y), a, b,
                 theta1=0, theta2=45, edgecolor='r', lw=1.5))
plt.show()

I'm guessing this is because the aspect ratio of the ellipse isn't 1

@pdhall99
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pdhall99 commented Feb 8, 2017

I'm trying to run your example, but you haven't specified angle_deg anywhere in the code (so adding the patches fails).

Thanks for pointing out that error. I've corrected it in the original report.

@dstansby dstansby added this to the 2.1 (next point release) milestone Feb 8, 2017
@dstansby dstansby self-assigned this Feb 8, 2017
@dstansby dstansby mentioned this issue Feb 8, 2017
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