Added sections to gallery of examples

Modified travis_script.sh to account for the new structure of the gallery Added README.txt files in directories of gallery examples Fixed references to gallery images in user guide pages Fixed broken links
2026-07-20 12:40:31 +08:00 · 2015-12-19 15:28:15 +01:00
parent 827e4b11c9
commit 55f5103dd8
84 changed files with 45 additions and 31 deletions
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+"""
+==================================
+Approximate and subdivide polygons
+==================================
+
+This example shows how to approximate (Douglas-Peucker algorithm) and subdivide
+(B-Splines) polygonal chains.
+
+"""
+from __future__ import print_function
+
+import numpy as np
+import matplotlib.pyplot as plt
+
+from skimage.draw import ellipse
+from skimage.measure import find_contours, approximate_polygon, \
+    subdivide_polygon
+
+
+hand = np.array([[1.64516129, 1.16145833],
+                 [1.64516129, 1.59375],
+                 [1.35080645, 1.921875],
+                 [1.375, 2.18229167],
+                 [1.68548387, 1.9375],
+                 [1.60887097, 2.55208333],
+                 [1.68548387, 2.69791667],
+                 [1.76209677, 2.56770833],
+                 [1.83064516, 1.97395833],
+                 [1.89516129, 2.75],
+                 [1.9516129, 2.84895833],
+                 [2.01209677, 2.76041667],
+                 [1.99193548, 1.99479167],
+                 [2.11290323, 2.63020833],
+                 [2.2016129, 2.734375],
+                 [2.25403226, 2.60416667],
+                 [2.14919355, 1.953125],
+                 [2.30645161, 2.36979167],
+                 [2.39112903, 2.36979167],
+                 [2.41532258, 2.1875],
+                 [2.1733871, 1.703125],
+                 [2.07782258, 1.16666667]])
+
+# subdivide polygon using 2nd degree B-Splines
+new_hand = hand.copy()
+for _ in range(5):
+    new_hand = subdivide_polygon(new_hand, degree=2, preserve_ends=True)
+
+# approximate subdivided polygon with Douglas-Peucker algorithm
+appr_hand = approximate_polygon(new_hand, tolerance=0.02)
+
+print("Number of coordinates:", len(hand), len(new_hand), len(appr_hand))
+
+fig, (ax1, ax2) = plt.subplots(ncols=2, figsize=(9, 4))
+
+ax1.plot(hand[:, 0], hand[:, 1])
+ax1.plot(new_hand[:, 0], new_hand[:, 1])
+ax1.plot(appr_hand[:, 0], appr_hand[:, 1])
+
+
+# create two ellipses in image
+img = np.zeros((800, 800), 'int32')
+rr, cc = ellipse(250, 250, 180, 230, img.shape)
+img[rr, cc] = 1
+rr, cc = ellipse(600, 600, 150, 90, img.shape)
+img[rr, cc] = 1
+
+plt.gray()
+ax2.imshow(img)
+
+# approximate / simplify coordinates of the two ellipses
+for contour in find_contours(img, 0):
+    coords = approximate_polygon(contour, tolerance=2.5)
+    ax2.plot(coords[:, 1], coords[:, 0], '-r', linewidth=2)
+    coords2 = approximate_polygon(contour, tolerance=39.5)
+    ax2.plot(coords2[:, 1], coords2[:, 0], '-g', linewidth=2)
+    print("Number of coordinates:", len(contour), len(coords), len(coords2))
+
+ax2.axis((0, 800, 0, 800))
+
+plt.show()