title: OpenCV errors for iOS / detecting Hough Circles
body: <p>I have been trying for hours to run an xcode project with openCV. I have built the source, imported it into the project and included 
     #ifdef __cplusplus #import opencv2/opencv.hpp>
     #endif
  in the .pch file.</p>
  
  <p>I followed the instructions from <a href="http://docs.opencv.org/trunk/doc/tutorials/introduction/ios_install/ios_install.html" rel="nofollow">http://docs.opencv.org/trunk/doc/tutorials/introduction/ios_install/ios_install.html</a></p>
  
  <p>Still I am getting many Apple Mach-O linker errors when I compile.</p>
  
  <pre><code>Undefined symbols for architecture i386:
   "std::__1::__vector_base_common&lt;true&gt;::__throw_length_error() const", referenced from:
  </code></pre>
  
  <p>Please help me I am really lost..</p>
  
  <p>UPDATE:</p>
  
  <p>Errors all fixed and now I am trying to detect circles..</p>
  
  <pre><code>Mat src, src_gray;
  
  cvtColor( image, src_gray, CV_BGR2GRAY );
  
  vector&lt;Vec3f&gt; circles;
  
  /// Apply the Hough Transform to find the circles
  HoughCircles( src_gray, circles, CV_HOUGH_GRADIENT, 1, image.rows/8, 200, 100, 0, 0 );
  
  
  /// Draw the circles detected
  for( size_t i = 0; i &lt; circles.size(); i++ )
  {
      Point center(cvRound(circles[i][0]), cvRound(circles[i][1]));
      int radius = cvRound(circles[i][2]);
      // circle center
      circle( src, center, 3, Scalar(0,255,0), -1, 8, 0 );
      // circle outline
      circle( src, center, radius, Scalar(0,0,255), 3, 8, 0 );
  
  
  }
  </code></pre>
  
  <p>I am using the code above, however no circles are being drawn on the image.. is there something obvious that I am doing wrong?</p>