title: Why epiplolar geometry/sfm does not give proper values in python opencv
body: <p>I tried to find rotation/translation between two images.</p>
  <p>For simplest case, I use two exact same images, and checked whether it gives 0 translations and rotations(identity matrix).</p>
  <p>However it does not give the results that I expected. why???</p>
  <p><a href="https://i.stack.imgur.com/xIcHP.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xIcHP.jpg" alt="enter image description here" /></a></p>
  <p>ORB feature is used and ten matched features are used to find Essential matrix and R/t. Result is (they are identical images):</p>
  <pre><code>t =  [[ 0.57735027] [-0.57735027] [ 0.57735027]]
  r = [[-0.33333333 -0.66666667  0.66666667]
       [-0.66666667 -0.33333333 -0.66666667]
       [ 0.66666667 -0.66666667 -0.33333333]]
  </code></pre>
  <p>What I expected is :</p>
  <pre><code>t = [[0, 0, 0]]
  r = [[1, 0, 0], [0, 1, 0], [0, 0, 0]]
  </code></pre>
  <p>Why it does not give strange results?</p>
  <pre><code>    orb = cv2.ORB_create()
      img1 = self.img1
      img2 = self.img2
  
      gray2 = cv2.cvtColor(img2, cv2.COLOR_BGR2GRAY)
      gray1 = cv2.cvtColor(img1, cv2.COLOR_BGR2GRAY)
  
      kpts1, descs1 = orb.detectAndCompute(gray1, None)
      kpts2, descs2 = orb.detectAndCompute(gray2, None)
  
      bf = cv2.BFMatcher(cv2.NORM_HAMMING, crossCheck=True)
      matches = bf.match(descs1, descs2)
      dmatches = sorted(matches, key=lambda x: x.distance)
  
      src_pts = np.float32([kpts1[m.queryIdx].pt for m in dmatches]).reshape(-1, 1, 2)
      src_pts = src_pts[0:10]
      dst_pts = np.float32([kpts2[m.trainIdx].pt for m in dmatches]).reshape(-1, 1, 2)
      dst_pts = dst_pts[0:10]
  
      K = np.array([[842.102288, 0., 263.697271],
                    [0., 833.300569, 536.024168],
                    [0., 0., 1.]])
  
      E, mask2 = cv2.findEssentialMat(src_pts, dst_pts, K, cv2.RANSAC, 0.999, 1.0);
      points, R, t, mask = cv2.recoverPose(E, src_pts, dst_pts)
  </code></pre>
  <p>test image (image1=image2=img)
  <a href="https://i.stack.imgur.com/qNT0F.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qNT0F.png" alt="enter image description here" /></a></p>