title: ExtractSURF always returning the same direction
body: <p>I'm just trying to start learning OpenCV. My understanding is ExtractSURF should return an angle between 0 and 360. For some reason keypoints always returning a direction of 90 for me. Any ideas why?</p>
  
  <p>This code:</p>
  
  <pre><code>import cv
  image = cv.LoadImageM('lena.bmp', cv.CV_LOAD_IMAGE_GRAYSCALE)
  (keypoints, descriptors) = cv.ExtractSURF(image, None, cv.CreateMemStorage(), (0, 6000, 1, 3))
  for keypoint in keypoints:
      ((x, y), laplacian, size, dir, hessian) = keypoint
      print "x=%d y=%d laplacian=%d size=%f dir=%f hessian=%f" % (x, y, laplacian, size, dir, hessian)
  </code></pre>
  
  <p>returns</p>
  
  <pre><code>x=345 y=201 laplacian=1 size=22.000000 dir=90.000000 hessian=6674.604492
  x=82 y=270 laplacian=-1 size=18.000000 dir=90.000000 hessian=7615.113770
  x=90 y=278 laplacian=-1 size=15.000000 dir=90.000000 hessian=12525.487305
  x=112 y=254 laplacian=1 size=22.000000 dir=90.000000 hessian=8894.154297
  x=273 y=274 laplacian=-1 size=24.000000 dir=90.000000 hessian=16313.005859
  x=154 y=319 laplacian=-1 size=15.000000 dir=90.000000 hessian=9818.360352
  x=172 y=333 laplacian=-1 size=26.000000 dir=90.000000 hessian=8314.745117
  x=137 y=386 laplacian=-1 size=15.000000 dir=90.000000 hessian=9148.833984
  x=140 y=363 laplacian=-1 size=22.000000 dir=90.000000 hessian=7735.985840
  </code></pre>