add example script for regionprops function to documentation

doc/examples/plot_regionprops.py

@@ -0,0 +1,64 @@
+"""
+=========================
+Measure region properties
+=========================
+
+This example shows how to measure properties of labelled image regions.
+"""
+
+import math
+import matplotlib.pyplot as plt
+import numpy as np
+
+from skimage.draw import ellipse
+from skimage.morphology import label
+from skimage.measure import regionprops
+from scipy.ndimage import geometric_transform
+
+
+ANGLE = 0.2
+
+def rotate(xy):
+    x, y = xy
+    out_x = math.cos(ANGLE) * x - math.sin(ANGLE) * y
+    out_y = math.sin(ANGLE) * x + math.cos(ANGLE) * y
+    return (out_x, out_y)
+
+image = np.zeros((600, 600), 'int')
+
+rr, cc = ellipse(300, 350, 100, 220)
+image[rr,cc] = 1
+
+image = geometric_transform(image, rotate)
+
+label_img = label(image)
+props = regionprops(label_img, [
+    'BoundingBox',
+    'Centroid',
+    'Orientation',
+    'MajorAxisLength',
+    'MinorAxisLength'
+])
+
+plt.imshow(image)
+
+for prop in props:
+    x0 = prop['Centroid'][1]
+    y0 = prop['Centroid'][0]
+    x1 = x0 + math.cos(prop['Orientation']) * 0.5 * prop['MajorAxisLength']
+    y1 = y0 - math.sin(prop['Orientation']) * 0.5 * prop['MajorAxisLength']
+    x2 = x0 - math.sin(prop['Orientation']) * 0.5 * prop['MinorAxisLength']
+    y2 = y0 - math.cos(prop['Orientation']) * 0.5 * prop['MinorAxisLength']
+
+    plt.plot((x0, x1), (y0, y1), '-r', linewidth=2.5)
+    plt.plot((x0, x2), (y0, y2), '-r', linewidth=2.5)
+    plt.plot(x0, y0, '.g', markersize=15)
+
+    minr, minc, maxr, maxc = prop['BoundingBox']
+    bx = (minc, maxc, maxc, minc, minc)
+    by = (minr, minr, maxr, maxr, minr)
+    plt.plot(bx, by, '-b', linewidth=2.5)
+
+plt.gray()
+plt.axis((0, 600, 600, 0))
+plt.show()