text: """
  ================
  Corner detection
  ================
  
  Detect corner points using the Harris corner detector and determine the
  subpixel position of corners ([1]_, [2]_).
  
  .. [1] https://en.wikipedia.org/wiki/Corner_detection
  .. [2] https://en.wikipedia.org/wiki/Interest_point_detection
  
  """
  from matplotlib import pyplot as plt
  
  from skimage import data
  from skimage.feature import corner_harris, corner_subpix, corner_peaks
  from skimage.transform import warp, AffineTransform
  from skimage.draw import ellipse
  
  # Sheared checkerboard
  tform = AffineTransform(scale=(1.3, 1.1), rotation=1, shear=0.7,
                          translation=(110, 30))
  image = warp(data.checkerboard()[:90, :90], tform.inverse,
               output_shape=(200, 310))
  # Ellipse
  rr, cc = ellipse(160, 175, 10, 100)
  image[rr, cc] = 1
  # Two squares
  image[30:80, 200:250] = 1
  image[80:130, 250:300] = 1
  
  coords = corner_peaks(corner_harris(image), min_distance=5, threshold_rel=0.02)
  coords_subpix = corner_subpix(image, coords, window_size=13)
  
  fig, ax = plt.subplots()
  ax.imshow(image, cmap=plt.cm.gray)
  ax.plot(coords[:, 1], coords[:, 0], color='cyan', marker='o',
          linestyle='None', markersize=6)
  ax.plot(coords_subpix[:, 1], coords_subpix[:, 0], '+r', markersize=15)
  ax.axis((0, 310, 200, 0))
  plt.show()
  