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update polygon example with subdivision

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This commit is contained in:
Johannes Schönberger
2012-08-15 08:55:43 +02:00
committed by Stefan van der Walt
parent 339c33eac3
commit 76c3574755
1 changed files with 14 additions and 17 deletions
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doc/examples/plot_approximate_polygon.py → doc/examples/plot_polygon.py
+14 -17
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@@ -9,18 +9,11 @@ algorithm.
import numpy as np
import matplotlib.pyplot as plt
from scipy import signal
from skimage.draw import ellipse
from skimage.measure import find_contours, approximate_polygon
from skimage.measure import find_contours, approximate_polygon, \
subdivide_polygon
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
hand = np.array([[1.64516129, 1.16145833],
[1.64516129, 1.59375 ],
[1.35080645, 1.921875 ],
@@ -44,17 +37,12 @@ hand = np.array([[1.64516129, 1.16145833],
[2.1733871 , 1.703125 ],
[2.07782258, 1.16666667]])
def doo_sabin_subdivision(points):
new_points = np.zeros((2 * (len(points) - 1), 2))
new_points[::2] = 3 / 4. * points[:-1] + 1 / 4. * points[1:]
new_points[1::2] = 1 / 4. * points[:-1] + 3 / 4. * points[1:]
return new_points
# subdivide polygon using 2nd degree B-Splines
new_hand = hand.copy()
for _ in range(5):
new_hand = doo_sabin_subdivision(new_hand)
new_hand = subdivide_polygon(new_hand, degree=2)
# 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)
@@ -65,9 +53,18 @@ 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)