title: OpenCV Error when using miniflann
body: <p>I found this code online .. and I wanted to try it > </p>
  
  <pre><code>int main( int argc, char **argv )
  {
  
  VideoCapture cam1, cam2; //Middle and left cameras
  //VideoCapture cam3; //Right camera
  
  cam1.open(0);
  cam2.open(1);
  //cam3.open(2);
  
  cam1.set(CV_CAP_PROP_FRAME_WIDTH, 320);
  cam1.set(CV_CAP_PROP_FRAME_HEIGHT, 240);
  
  cam2.set(CV_CAP_PROP_FRAME_WIDTH, 320);
  cam2.set(CV_CAP_PROP_FRAME_HEIGHT, 240);
  
  //cam3.set(CV_CAP_PROP_FRAME_WIDTH, 320);
  //cam3.set(CV_CAP_PROP_FRAME_HEIGHT, 240);
  Mat frm1, frm2;
  
  while(1)
  {
      //Step 1: Get frames from a few cameras
  
      cam1 &gt;&gt; frm1; //Reference plane
      cam2 &gt;&gt; frm2; //Right-side target plane
      // cam3 &gt;&gt; frm3;
  
      if( frm1.empty()||frm2.empty() )
          break;
  
  
      //Step2: SURF detection
      int minHessian = 800;
  
      SurfFeatureDetector detector( minHessian );
      vector&lt;KeyPoint&gt; keypoints_1, keypoints_2;
  
      detector.detect( frm1, keypoints_1 );
      detector.detect( frm2, keypoints_2 );
  
      SurfDescriptorExtractor extractor; ///
      Mat descriptors_1, descriptors_2;
      extractor.compute( frm1, keypoints_1, descriptors_1 );
      extractor.compute( frm2, keypoints_2, descriptors_2 );
  
  
      //Step 3: Feature matching
      //-- Matching descriptor vectors with a matcher
      FlannBasedMatcher matcher;
      vector&lt; DMatch &gt; matches;
      matcher.match( descriptors_1, descriptors_2, matches);
      //vector&lt; vector&lt;DMatch&gt; &gt; matches;
      //matcher.knnMatch( descriptors_1, descriptors_2, matches,2);
  
  
      double max_dist = 0; double min_dist = 50;
  
  
      //-- Quick calculation of max and min distances between keypoints
      for( int i = 0; i &lt; descriptors_1.rows; i++ )
      { double dist = matches[i].distance;
          if( dist &lt; min_dist ) min_dist = dist;
          if( dist &gt; max_dist ) max_dist = dist;
      }
  
      //printf("-- Max dist : %f \n", max_dist );
      //printf("-- Min dist : %f \n", min_dist );
  
      //-- Draw only "good" matches (i.e. whose distance is less than 3*min_dist )
      vector&lt; DMatch &gt; good_matches;
  
      for( int i = 0; i &lt; descriptors_1.rows; i++ )
      { if( matches[i].distance &lt; 2*min_dist )
          { good_matches.push_back( matches[i]); }
      }
  
      Mat img_matches;
      drawMatches( frm1, keypoints_1, frm2, keypoints_2,
                  good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
                  vector&lt;char&gt;(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS );
  
  
      //-- Localize the object from frame1 in frame2
      vector&lt;Point2f&gt; frame1;
      vector&lt;Point2f&gt; frame2;
  
      for( int i = 0; i &lt; good_matches.size(); i++ )
      {
          //-- Get the keypoints from the good matches
          frame1.push_back( keypoints_1[ good_matches[i].queryIdx ].pt );
          frame2.push_back( keypoints_2[ good_matches[i].trainIdx ].pt );
      }
  
  
      //Step 4: RANSAC and Homography
  
      Mat H = findHomography( Mat(frame2), Mat(frame1), CV_RANSAC, 5.0 );
      cout &lt;&lt; "Homography for mapping the r-side plane to the ref. plane: " &lt;&lt; endl &lt;&lt; H &lt;&lt; endl;
      //-- Show detected matches
      imshow("Matches", img_matches );
  
      //Step 5:Warping
  
      Mat result;
      warpPerspective(frm2,result,H,Size(3*frm1.cols,1.5*frm1.rows));
      imshow("Warping result",result);
      Mat half(result,Rect(0,0,frm2.cols,frm2.rows));
      frm1.copyTo(half);//Reference image
  
      //Step 6:Blending
  
      //Step 7:Showing the panoramic video
  
      imshow("Blended view",result);
      char c=waitKey(20);
      if (c==27)
          break;
  }
  
  
  return 0;
  }
  </code></pre>
  
  <p>However, when I try to run the code, I found this error .. I checked the code in the OpenCV tutorial as well and they are almost exactly the same until the findhomography part.  </p>
  
  <pre><code>OpenCV Error: Unsupported format or combination of formats
  (type=0) in buildIndex_, file OpenCV-2.3.1/modules/flann/src/miniflann.cpp,
  line 297 terminate called after throwing an instance of 'cv::Exception' what()
  OpenCV-2.3.1/modules/flann/src/miniflann.cpp:297: error:
  (-210) type=0 in function buildIndex_
  </code></pre>
  
  <p>Any ideas what could went wrong here ? </p>
  
  <p>thank you </p>