title: Use Euclidean distance in SURF
body: <p>In my code I'm filtering the good images based on the nearest neigbour distance ratio, as follows:</p>
  
  <pre><code>for(int i = 0; i &lt; min(des_image.rows-1,(int) matches.size()); i++) 
  {
          if((matches[i][0].distance &lt; 0.6*(matches[i][1].distance)) &amp;&amp; 
                                    ((int)matches[i].size()&lt;=2 &amp;&amp; (int)matches[i].size()&gt;0))
          {
              good_matches.push_back(matches[i][0]);
          }
   }
  </code></pre>
  
  <p>Since I'm filtering the good images based on the nearest neighbor distance ratio, do I need to still do Euclidean distance calculation?</p>
  
  <p>And I want to know when I use the <code>knnMatch</code> method in <code>FlannBasedMatcher</code>, inside the method do they use the Euclidean distance to match the keypoints?</p>