title: findFundamentalMat - epipolar lines are wrong
body: <p>I want to compute the fundamental matrix between two image pairs. For that purpose I use SIFT-Features which are matched via the <code>cv::FlannBasedMatcher</code>. Afterwards i call <code>cv::findFundamentalMat(left_pts, right_pts, CV_RANSAC, 2.0, 0.99, ransac_mask)</code> with the found matches. </p>
  
  <p>To visualize the computed fundamental matrix I want to draw epipolar-lines. To do that I tried the <code>cv::computeCorrespondEpilines</code> and a manual mulplication with a Point and extraction of the resulting line equation (ax + by + c = 0). </p>
  
  <p>To draw the lines I simply use that snipped (which I've found in many other examples)</p>
  
  <pre><code>for (cv::vector&lt;cv::Vec3f&gt;::const_iterator it = lines1.begin(); it!=lines1.end(); ++it)
  {
      cv::line(left_new,
           cv::Point(0,-(*it)[2]/(*it)[1]),
           cv::Point(left.cols,-((*it)[2] + (*it)[0]*left.cols)/(*it)[1]),
           cv::Scalar(255,255,255));
  }
  </code></pre>
  
  <p>But corresponding points are not on the epipolar lines. I've even tried it on already rectified images but the lines are not horizontal.</p>
  
  <p>Now i've also tested that example:
  <a href="http://opencv-cookbook.googlecode.com/svn/trunk/Chapter%2009/estimateF.cpp" rel="nofollow">http://opencv-cookbook.googlecode.com/svn/trunk/Chapter%2009/estimateF.cpp</a>
  only to find out that it has the same problem.</p>
  
  <p>Can someone share a working example for such a use-case or give me a hint what could go wrong? (Matchings seem to be fine so it has to be something with the actual estimation)</p>