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Fix quiver key plot when angles='xy' and/or scale_units='xy' #27044

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Jan 24, 2024
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Fix quiver key plot when angles='xy' and/or scale_units='xy' #27044

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30 changes: 17 additions & 13 deletions lib/matplotlib/quiver.py
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Original file line number Diff line number Diff line change
Expand Up @@ -263,7 +263,7 @@ def __init__(self, Q, X, Y, U, label,
The key label (e.g., length and units of the key).
angle : float, default: 0
The angle of the key arrow, in degrees anti-clockwise from the
x-axis.
horizontal axis.
coordinates : {'axes', 'figure', 'data', 'inches'}, default: 'axes'
Coordinate system and units for *X*, *Y*: 'axes' and 'figure' are
normalized coordinate systems with (0, 0) in the lower left and
Expand Down Expand Up @@ -327,10 +327,8 @@ def _init(self):
Umask=ma.nomask):
u = self.U * np.cos(np.radians(self.angle))
v = self.U * np.sin(np.radians(self.angle))
angle = (self.Q.angles if isinstance(self.Q.angles, str)
else 'uv')
self.verts = self.Q._make_verts(
np.array([u]), np.array([v]), angle)
self.verts = self.Q._make_verts([[0., 0.]],
np.array([u]), np.array([v]), 'uv')
kwargs = self.Q.polykw
kwargs.update(self.kw)
self.vector = mcollections.PolyCollection(
Expand Down Expand Up @@ -521,7 +519,7 @@ def _init(self):
# _make_verts sets self.scale if not already specified
if (self._dpi_at_last_init != self.axes.figure.dpi
and self.scale is None):
self._make_verts(self.U, self.V, self.angles)
self._make_verts(self.XY, self.U, self.V, self.angles)

self._dpi_at_last_init = self.axes.figure.dpi

Expand All @@ -537,7 +535,7 @@ def get_datalim(self, transData):
@martist.allow_rasterization
def draw(self, renderer):
self._init()
verts = self._make_verts(self.U, self.V, self.angles)
verts = self._make_verts(self.XY, self.U, self.V, self.angles)
self.set_verts(verts, closed=False)
super().draw(renderer)
self.stale = False
Expand Down Expand Up @@ -594,33 +592,38 @@ def _set_transform(self):
self.set_transform(trans)
return trans

def _angles_lengths(self, U, V, eps=1):
xy = self.axes.transData.transform(self.XY)
# Calculate angles and lengths for segment between (x, y), (x+u, y+v)
def _angles_lengths(self, XY, U, V, eps=1):
xy = self.axes.transData.transform(XY)
uv = np.column_stack((U, V))
xyp = self.axes.transData.transform(self.XY + eps * uv)
xyp = self.axes.transData.transform(XY + eps * uv)
dxy = xyp - xy
angles = np.arctan2(dxy[:, 1], dxy[:, 0])
lengths = np.hypot(*dxy.T) / eps
return angles, lengths

def _make_verts(self, U, V, angles):
# XY is stacked [X, Y].
# See quiver() doc for meaning of X, Y, U, V, angles.
def _make_verts(self, XY, U, V, angles):
uv = (U + V * 1j)
str_angles = angles if isinstance(angles, str) else ''
if str_angles == 'xy' and self.scale_units == 'xy':
# Here eps is 1 so that if we get U, V by diffing
# the X, Y arrays, the vectors will connect the
# points, regardless of the axis scaling (including log).
angles, lengths = self._angles_lengths(U, V, eps=1)
angles, lengths = self._angles_lengths(XY, U, V, eps=1)
elif str_angles == 'xy' or self.scale_units == 'xy':
# Calculate eps based on the extents of the plot
# so that we don't end up with roundoff error from
# adding a small number to a large.
eps = np.abs(self.axes.dataLim.extents).max() * 0.001
angles, lengths = self._angles_lengths(U, V, eps=eps)
angles, lengths = self._angles_lengths(XY, U, V, eps=eps)

if str_angles and self.scale_units == 'xy':
a = lengths
else:
a = np.abs(uv)

if self.scale is None:
sn = max(10, math.sqrt(self.N))
if self.Umask is not ma.nomask:
Expand All @@ -630,6 +633,7 @@ def _make_verts(self, U, V, angles):
# crude auto-scaling
# scale is typical arrow length as a multiple of the arrow width
scale = 1.8 * amean * sn / self.span

if self.scale_units is None:
if self.scale is None:
self.scale = scale
Expand Down
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56 changes: 56 additions & 0 deletions lib/matplotlib/tests/test_quiver.py
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Original file line number Diff line number Diff line change
Expand Up @@ -267,6 +267,62 @@ def test_quiverkey_angles():
assert len(qk.verts) == 1


def test_quiverkey_angles_xy_aitoff():
# GH 26316 and GH 26748
# Test that only one arrow will be plotted with non-cartesian
# when angles='xy' and/or scale_units='xy'

# only for test purpose
# scale_units='xy' may not be a valid use case for non-cartesian
kwargs_list = [
{'angles': 'xy'},
{'angles': 'xy', 'scale_units': 'xy'},
{'scale_units': 'xy'}
]

for kwargs_dict in kwargs_list:

x = np.linspace(-np.pi, np.pi, 11)
y = np.ones_like(x) * np.pi / 6
vx = np.zeros_like(x)
vy = np.ones_like(x)

fig = plt.figure()
ax = fig.add_subplot(projection='aitoff')
q = ax.quiver(x, y, vx, vy, **kwargs_dict)
qk = ax.quiverkey(q, 0, 0, 1, '1 units')

fig.canvas.draw()
assert len(qk.verts) == 1


def test_quiverkey_angles_scale_units_cartesian():
# GH 26316
# Test that only one arrow will be plotted with normal cartesian
# when angles='xy' and/or scale_units='xy'

kwargs_list = [
{'angles': 'xy'},
{'angles': 'xy', 'scale_units': 'xy'},
{'scale_units': 'xy'}
]

for kwargs_dict in kwargs_list:
X = [0, -1, 0]
Y = [0, -1, 0]
U = [1, -1, 1]
V = [1, -1, 0]

fig, ax = plt.subplots()
q = ax.quiver(X, Y, U, V, **kwargs_dict)
ax.quiverkey(q, X=0.3, Y=1.1, U=1,
label='Quiver key, length = 1', labelpos='E')
qk = ax.quiverkey(q, 0, 0, 1, '1 units')

fig.canvas.draw()
assert len(qk.verts) == 1


def test_quiver_setuvc_numbers():
"""Check that it is possible to set all arrow UVC to the same numbers"""

Expand Down