title: SIFT feature_matching point coordinates
body: <p>I want to print the detect features keypoints with the FLANN based Matcher
   Algorithm : <a href="http://docs.opencv.org/trunk/dc/dc3/tutorial_py_matcher.html" rel="nofollow noreferrer">http://docs.opencv.org/trunk/dc/dc3/tutorial_py_matcher.html</a>.
  The search works fine and show as the tutorial the keypoints in red(all) and green(good).
  I want only print the coordinates(x,y) named here ‘kp2’ of the second image(scene) but it doesn’t work.
  Here is my code :</p>
  
  <pre><code>import numpy as np
  import cv2
  from matplotlib import pyplot as plt
  img1 = cv2.imread('img1.jpg',0)          # queryImage
  img2 = cv2.imread('img2.jpg',0) # trainImage
  # Initiate SIFT detector
  sift = cv2.xfeatures2d.SIFT_create()
  # find the keypoints and descriptors with SIFT
  kp1, des1 = sift.detectAndCompute(img1,None)
  kp2, des2 = sift.detectAndCompute(img2,None)
  # FLANN parameters
  FLANN_INDEX_KDTREE = 1
  index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5)
  search_params = dict(checks=50)   # or pass empty dictionary
  flann = cv2.FlannBasedMatcher(index_params,search_params)
  matches = flann.knnMatch(des1,des2,k=2)
  # Need to draw only good matches, so create a mask
  matchesMask = [[0,0] for i in range(len(matches))]
  
  # ratio test as per Lowe's paper
  for i,(m,n) in enumerate(matches):
      if m.distance &lt; 0.7*n.distance:
          matchesMask[i]=[1,0]
          print(i,kp2[i].pt)
  
  draw_params = dict(matchColor = (0,255,0),
                     singlePointColor = (255,0,0),
                     matchesMask = matchesMask,
                     flags = 0)
  img3 = cv2.drawMatchesKnn(img1,kp1,img2,kp2,matches,None,**draw_params)
  plt.imshow(img3,),plt.show()
  </code></pre>
  
  <p>My result :</p>
  
  <pre><code>77 (67.68722534179688, 92.98455047607422)
  82 (14.395119667053223, 93.1697998046875)
  86 (127.58460235595703, 98.1304931640625)
  109 (66.52041625976562, 111.51738739013672)
  110 (66.52041625976562, 111.51738739013672)
  146 (69.3978500366211, 11.287369728088379)
  </code></pre>
  
  <p>The number of match keypoints is good but the coordinates are wrong <strong>print(i,kp2[i].pt)</strong>. I checked with the original image.
  What I did wrong and if yes which lines I have to put to print only the match keypoints coordinates.
  Thanks for all.</p>