title: How to transfer KeyPointVector to Mat in javaCV
body: <p>I want to make an calcOpticalFlowPyrLK from feature points get from image, when I use goodFeaturesToTrack, everything is OK as following:</p>
  
  <pre><code>goodFeaturesToTrack(blackOutImagePrev, prevCorners, 200, 0.04, 30);
  calcOpticalFlowPyrLK(blackOutImagePrev, blackOutImageNext, prevCorners, nextCorners, status, err);
  </code></pre>
  
  <p>Due to the processing speed issue, I want to change the function that I get feature points to surf or fast method. For the surf, the function is:</p>
  
  <pre><code>final KeyPointVector kp = new KeyPointVector();
  final SURF surf = SURF.create(2500, 4, 2, true, false);
  surf.detect(image, kp);
  </code></pre>
  
  <p>Since the surf get feature points are stored in KeyPointVector, but the type of prevCorners is Mat. How could I transfer it to Mat so I can call the calcOpticalFlowPyrLK? Or there is any workaround?  </p>