8000 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

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Merged
merged 2 commits into from
Mar 10, 2017
Merged

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

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4bc50da
Correct theta values when drawing a non-circular ellipse
dstansby Feb 8, 2017
0376d83
Fix small typo in api change
dstansby Mar 2, 2017
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8 changes: 8 additions & 0 deletions doc/api/api_changes/2017-02-10-DS_elliptical_arc_angle.rst
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@@ -0,0 +1,8 @@
Elliptical arcs now drawn between correct angles
````````````````````````````````````````````````

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,
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are -> arc

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woops...

so the resulting arc did not lie between *theta1* and *theta2*.
20 changes: 13 additions & 7 deletions lib/matplotlib/patches.py
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Expand Up @@ -1554,8 +1554,6 @@ def __init__(self, xy, width, height, angle=0.0,
self.theta1 = theta1
self.theta2 = theta2

self._path = Path.arc(self.theta1, self.theta2)

@allow_rasterization
def draw(self, renderer):
"""
Expand Down Expand Up @@ -1607,15 +1605,25 @@ def draw(self, renderer):

self._recompute_transform()

# Get the width and height in pixels
width = self.convert_xunits(self.width)
height = self.convert_yunits(self.height)

# If the width and height of ellipse are not equal, take into account
# stretching when calculating angles to draw between
def theta_stretch(theta, scale):
theta = np.deg2rad(theta)
x = np.cos(theta)
y = np.sin(theta)
return np.rad2deg(np.arctan2(scale * y, x))
theta1 = theta_stretch(self.theta1, width / height)
theta2 = theta_stretch(self.theta2, width / height)

# Get width and height in pixels
width, height = self.get_transform().transform_point(
(width, height))
inv_error = (1.0 / 1.89818e-6) * 0.5

if width < inv_error and height < inv_error:
# self._path = Path.arc(self.theta1, self.theta2)
self._path = Path.arc(theta1, theta2)
return Patch.draw(self, renderer)

def iter_circle_intersect_on_line(x0, y0, x1, y1):
Expand Down Expand Up @@ -1670,8 +1678,6 @@ def iter_circle_intersect_on_line_seg(x0, y0, x1, y1):
self.get_transform().inverted()
box_path = box_path.transformed(box_path_transform)

theta1 = self.theta1
theta2 = self.theta2
thetas = set()
# For each of the point pairs, there is a line segment
for p0, p1 in zip(box_path.vertices[:-1], box_path.vertices[1:]):
Expand Down
Binary file added lib/matplotlib/tests/baseline_images/test_axes/arc_angles.png
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42 changes: 34 additions & 8 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -982,6 +982,32 @@ def test_canonical():
ax.plot([1, 2, 3])


@image_comparison(baseline_images=['arc_angles'], remove_text=True,
style='default', extensions=['png'])
def test_arc_angles():
from matplotlib import patches
# Ellipse parameters
w = 2
h = 1
centre = (0.2, 0.5)

fig, axs = plt.subplots(3, 3)
for i, ax in enumerate(axs.flat):
theta2 = i * 360 / 9
theta1 = theta2 - 45
ax.add_patch(patches.Ellipse(centre, w, h, alpha=0.3))
ax.add_patch(patches.Arc(centre, w, h, theta1=theta1, theta2=theta2))
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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?

# Straight lines intersecting start and end of arc
ax.plot([2 * np.cos(np.deg2rad(theta1)) + centre[0],
centre[0],
2 * np.cos(np.deg2rad(theta2)) + centre[0]],
[2 * np.sin(np.deg2rad(theta1)) + centre[1],
centre[1],
2 * np.sin(np.deg2rad(theta2)) + centre[1]])
ax.set_xlim(-2, 2)
ax.set_ylim(-2, 2)


@image_comparison(baseline_images=['arc_ellipse'],
remove_text=True)
def test_arc_ellipse():
Expand All @@ -990,23 +1016,23 @@ def test_arc_ellipse():
width, height = 1e-1, 3e-1
angle = -30

theta = np.arange(0.0, 360.0, 1.0)*np.pi/180.0
x = width/2. * np.cos(theta)
y = height/2. * np.sin(theta)
theta = np.arange(0.0, 360.0, 1.0) * np.pi / 180.0
x = width / 2. * np.cos(theta)
y = height / 2. * np.sin(theta)

rtheta = angle*np.pi/180.
rtheta = angle * np.pi / 180.
R = np.array([
[np.cos(rtheta), -np.sin(rtheta)],
[np.sin(rtheta), np.cos(rtheta)],
])
[np.cos(rtheta), -np.sin(rtheta)],
[np.sin(rtheta), np.cos(rtheta)]])

x, y = np.dot(R, np.array([x, y]))
x += xcenter
y += ycenter

fig = plt.figure()
ax = fig.add_subplot(211, aspect='auto')
ax.fill(x, y, alpha=0.2, facecolor='yellow', edgecolor='yellow', linewidth=1, zorder=1)
ax.fill(x, y, alpha=0.2, facecolor='yellow', edgecolor='yellow',
linewidth=1, zorder=1)

e1 = patches.Arc((xcenter, ycenter), width, height,
angle=angle, linewidth=2, fill=False, zorder=2)
Expand Down
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