title: opencv FLANN with ORB descriptors?
body: <p>I am trying to use FLANN with ORB descriptors, but opencv crashes with this simple code:</p>
  
  <pre><code>vector&lt;vector&lt;KeyPoint&gt; &gt; dbKeypoints;
  vector&lt;Mat&gt; dbDescriptors;
  vector&lt;Mat&gt; objects;   
  
  /*
    load Descriptors from images (with OrbDescriptorExtractor())
  */
  
  FlannBasedMatcher matcher;
  
  matcher.add(dbDescriptors); 
  matcher.train() //&gt; Crash!
  </code></pre>
  
  <p>If I use <code>SurfDescriptorExtractor()</code> it works well.</p>
  
  <p>How can I solve this?</p>
  
  <p>OpenCV says:</p>
  
  <pre><code>OpenCV Error: Unsupported format or combination of formats (type=0
  ) in unknown function, file D:\Value\Personal\Parthenope\OpenCV\modules\flann\sr
  c\miniflann.cpp, line 299
  </code></pre>