title: error in creation of Set from Points
body: <p>I want to have a set of all Pixel Coordinates of an image. Unfortunately i get the following error message:</p>
  
  <p>"error C2678: binary '&lt;' : no operator found which takes a left-hand operand of type 'const cv::Point' (or there is no acceptable conversion)"</p>
  
  <pre><code>Mat img;
  img = imread( "[...]\\picture.jpg", 1 );
  
  set&lt;Point&gt; pointset;
  for( int x = 0 ; x &lt; img.cols ; x++)
  {
      for (int y = 0 ; y &lt; img.rows ; y++)
      {
          pointset.insert(Point(x,y));
      }
  }
  </code></pre>
  
  <p>I suspect that every type that goes into a set has to provide functions for comparison and cv::Point fails to do that. Unfortunately I'm new to C++ and OpenCV and don't know how to check if my suspicion is true.</p>