added get_vertices and get_co_vertices methods the Ellipse

Author: Johann Krauter

galleries/examples/shapes_and_collections/ellipse_arrow.py

@@ -1,6 +1,6 @@
 """
 ===================================
-Ellipse with orientation arrow Demo
+Ellipse with orientation arrow demo
 ===================================
 
 This demo shows how to draw an ellipse with
@@ -9,98 +9,93 @@
 </gallery/shapes_and_collections/ellipse_collection>`.
 """
 
-from typing import Tuple
-
 import matplotlib.pyplot as plt
-import numpy as np
-
 from matplotlib.markers import MarkerStyle
 from matplotlib.patches import Ellipse
 from matplotlib.transforms import Affine2D
 
-# %%
-#
-# A method to calculate the end points of the ellipse major, minor axis
-# """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
-#
-# Calculates the minor axis and major axis end points of the ellipse.
-# It needs the ellipse parameter like width, height, angle.
-# The output are 2 lists of 2 xy coordinates
-# (minor((x0, y0), (x1, y1)), major((x0, y0), (x1, y1))).
-
-
-def getMinorMajor(ellipse: Ellipse) -> Tuple[list, list]:
-    """
-    Calculates the end points of minor and major axis of an ellipse.
-
-    Parameters
-    ----------
-    ellipse : ~matplotlib.patches.Ellipse
-        Ellipse patch.
-
-    Returns
-    -------
-    ~typing.Tuple[list, list]
-    """
-    # Calculate the endpoints of the minor axis
-    x0_minor = ellipse.center[0] - ellipse.height / 2 * np.sin(
-        np.deg2rad(ellipse.angle)
-    )
-    y0_minor = ellipse.center[1] + ellipse.height / 2 * np.cos(
-        np.deg2rad(ellipse.angle)
-    )
-    x1_minor = ellipse.center[0] + ellipse.height / 2 * np.sin(
-        np.deg2rad(ellipse.angle)
-    )
-    y1_minor = ellipse.center[1] - ellipse.height / 2 * np.cos(
-        np.deg2rad(ellipse.angle)
-    )
-
-    # Calculate the endpoints of the major axis
-    x0_major = ellipse.center[0] - ellipse.width / 2 * np.cos(np.deg2rad(ellipse.angle))
-    y0_major = ellipse.center[1] - ellipse.width / 2 * np.sin(np.deg2rad(ellipse.angle))
-    x1_major = ellipse.center[0] + ellipse.width / 2 * np.cos(np.deg2rad(ellipse.angle))
-    y1_major = ellipse.center[1] + ellipse.width / 2 * np.sin(np.deg2rad(ellipse.angle))
-    return [(x0_minor, y0_minor), (x1_minor, y1_minor)], [
-        (x0_major, y0_major),
-        (x1_major, y1_major),
-    ]
-
-
-# Define the ellipse
+
+# Create a figure and axis
+fig, ax = plt.subplots(1, 1, subplot_kw={"aspect": "equal"})
+
+# Define an ellipse clockwise
 center = (2, 4)
 width = 30
 height = 20
 angle = 35
-ellipse = Ellipse(
+ellipse_clockwise = Ellipse(
     xy=center,
     width=width,
     height=height,
     angle=angle,
     facecolor="none",
     edgecolor="b",
+    label="clockwise"
 )
 
-minor, major = getMinorMajor(ellipse)
-
-# Create a figure and axis
-fig, ax = plt.subplots(1, 1, subplot_kw={"aspect": "equal"})
+# Get position of vertex for arrow marker
+vertices = ellipse_clockwise.get_co_vertices()
 
 # Add the ellipse patch to the axis
-ax.add_patch(ellipse)
+ax.add_patch(ellipse_clockwise)
 
 # Plot a arrow marker at the end point of minor axis
-t = Affine2D().rotate_deg(angle)
+t = Affine2D().rotate_deg(ellipse_clockwise.angle)
 ax.plot(
-    minor[0][0],
-    minor[0][1],
+    vertices[0][0],
+    vertices[0][1],
     color="b",
     marker=MarkerStyle(">", "full", t),
-    markersize=10,
+    markersize=10
 )
 
+# Define an second ellipse counterclockwise
+center = (2, 4)
+width = 30
+height = 15
+angle = -20
+ellipse_counterclockwise = Ellipse(
+    xy=center,
+    width=width,
+    height=height,
+    angle=angle,
+    facecolor="none",
+    edgecolor="g",
+    label="counterclockwise"
+)
+
+# Add the ellipse patch to the axis
+ax.add_patch(ellipse_counterclockwise)
+
+# Get position of vertex for arrow marker
+vertices = ellipse_counterclockwise.get_co_vertices()
+
+# Plot a arrow marker at the end point of minor axis
+t = Affine2D().rotate_deg(ellipse_counterclockwise.angle)
+ax.plot(
+    vertices[0][0],
+    vertices[0][1],
+    color="g",
+    marker=MarkerStyle("<", "full", t),
+    markersize=10
+)
+
+
+plt.legend()
 plt.show()
 
+center = (2, 4)
+width = 30
+height = 20
+angle = 35
+ellipse = Ellipse(
+    xy=center,
+    width=width,
+    height=height,
+    angle=angle
+)
+print(ellipse.get_vertices())
+print(ellipse.get_co_vertices())
 
 # %%
 #

lib/matplotlib/patches.py

@@ -1654,6 +1654,30 @@ def get_corners(self):
         return self.get_patch_transform().transform(
             [(-1, -1), (1, -1), (1, 1), (-1, 1)])
 
+    def get_vertices(self):
+        """
+        Return the left and right vertex coordinates of the ellipse.
+
+        The definition can be found `here<https://en.wikipedia.org/wiki/Ellipse>`_
+        """
+        x0 = self._center[0] - self._width / 2 * np.cos(np.deg2rad(self._angle))
+        y0 = self._center[1] - self._width / 2 * np.sin(np.deg2rad(self._angle))
+        x1 = self._center[0] + self._width / 2 * np.cos(np.deg2rad(self._angle))
+        y1 = self._center[1] + self._width / 2 * np.sin(np.deg2rad(self._angle))
+        return [(x0, y0), (x1, y1)]
+    
+    def get_co_vertices(self):
+        """
+        Return the left and right co-vertex coordinates of the ellipse.
+        
+        The definition can be found `here<https://en.wikipedia.org/wiki/Ellipse>`_
+        """
+        x0 = self._center[0] - self._height / 2 * np.sin(np.deg2rad(self._angle))
+        y0 = self._center[1] + self._height / 2 * np.cos(np.deg2rad(self._angle))
+        x1 = self._center[0] + self._height / 2 * np.sin(np.deg2rad(self._angle))
+        y1 = self._center[1] - self._height / 2 * np.cos(np.deg2rad(self._angle))
+        return [(x0, y0), (x1, y1)]
+
 
 class Annulus(Patch):
     """

lib/matplotlib/tests/test_patches.py

@@ -104,6 +104,28 @@ def test_corner_center():
     assert_almost_equal(ellipse.get_corners(), corners_rot)
 
 
+def test_ellipse_vertices():
+    center = (2, 4)
+    width = 30
+    height = 20
+    angle = 35
+    ellipse = Ellipse(xy=center, width=width, height=height, angle=angle)
+    assert_almost_equal(
+        ellipse.get_vertices(),
+        [
+            (-10.287280664334878, -4.60364654526569),
+            (14.287280664334878, 12.60364654526569),
+        ],
+    )
+    assert_almost_equal(
+        ellipse.get_co_vertices(),
+        [
+            (-3.7357643635104605, 12.191520442889917),
+            (7.7357643635104605, -4.191520442889917),
+        ],
+    )
+
+
 def test_rotate_rect():
     loc = np.asarray([1.0, 2.0])
     width = 2