title: How to Access Points location on OpenCV Matcher?
body: <p>I am using this FLANN matcher algorithm to match interest points in 2 pictures the code is displayed below).</p>
  
  <p>There is a moment when the code finds a list of matched points:</p>
  
  <pre><code>std::vector&lt;DMatch&gt; good_matches;
  </code></pre>
  
  <p>I would like to get the points localization (x,y) in both pictures. To create a displacement map. <strong>How could I access these points localization?</strong></p>
  
  <p>Cheers,</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;iostream&gt;
  #include "opencv2/core/core.hpp"
  #include "opencv2/nonfree/features2d.hpp"
  #include "opencv2/highgui/highgui.hpp"
  
  using namespace cv;
  
  void readme();
  
  /** @function main */
  int main(int argc, char** argv) {
      if (argc != 3) {
          readme();
          return -1;
      }
  
      // Transform in GrayScale
      Mat img_1 = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
      Mat img_2 = imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE);
  
      // Checks if the image could be loaded
      if (!img_1.data || !img_2.data) {
          std::cout &lt;&lt; " --(!) Error reading images " &lt;&lt; std::endl;
          return -1;
      }
  
      //-- Step 1: Detect the keypoints using SURF Detector
      int minHessian = 400;
  
      SurfFeatureDetector detector(minHessian);
  
      std::vector&lt;KeyPoint&gt; keypoints_1, keypoints_2;
  
      detector.detect(img_1, keypoints_1);
      detector.detect(img_2, keypoints_2);
  
      //-- Step 2: Calculate descriptors (feature vectors)
      SurfDescriptorExtractor extractor;
  
      Mat descriptors_1, descriptors_2;
  
      extractor.compute(img_1, keypoints_1, descriptors_1);
      extractor.compute(img_2, keypoints_2, descriptors_2);
  
      //-- Step 3: Matching descriptor vectors using FLANN matcher
      FlannBasedMatcher matcher;
      std::vector&lt;DMatch&gt; matches;
      matcher.match(descriptors_1, descriptors_2, matches);
  
      double max_dist = 0;
      double min_dist = 100;
  
      //-- Quick calculation of max and min distances between keypoints
      for (int i = 0; i &lt; descriptors_1.rows; i++) {
          double dist = matches[i].distance;
  //      printf("-- DISTANCE =  [%f]\n", dist);
          if (dist &lt; min_dist)
              min_dist = dist;
          if (dist &gt; max_dist)
              max_dist = dist;
      }
  
      printf("-- Max dist : %f \n", max_dist);
      printf("-- Min dist : %f \n", min_dist);
  
      //-- Draw only "good" matches (i.e. whose distance is less than 2*min_dist )
      //-- PS.- radiusMatch can also be used here.
      std::vector&lt;DMatch&gt; good_matches;
  
      for (int i = 0; i &lt; descriptors_1.rows; i++) {
          if (matches[i].distance &lt; 2 * min_dist) {
              good_matches.push_back(matches[i]);
          }
      }
  
      //-- Draw only "good" matches
      Mat img_matches;
      drawMatches(img_1, keypoints_1, img_2, keypoints_2, good_matches,
              img_matches, Scalar::all(-1), Scalar::all(-1), vector&lt;char&gt;(),
              DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);
  
      //-- Show detected matches
      imshow("Good Matches", img_matches);
  
      for (int i = 0; i &lt; good_matches.size(); i++) {
          printf("-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  \n", i,
                  good_matches[i].queryIdx, good_matches[i].trainIdx);
      }
  
      waitKey(0);
  
      return 0;
  }
  
  /** @function readme */
  void readme() {
      std::cout &lt;&lt; " Usage: ./SURF_FlannMatcher &lt;img1&gt; &lt;img2&gt;" &lt;&lt; std::endl;
  }
  </code></pre>