title: OpenCV 3.0.0 SurfFeatureDetector and SurfDescriptorExtractor Errors
body: <p>I am attempting to implement the OpenCV 3.0.0 SURF Feature Description and Detection but after running the sample code on the OpenCV site, I receive a load of errors all related to SURF. Any idea of what could be going wrong? Thanks!</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;iostream&gt;
  #include "opencv2/core.hpp"
  #include "opencv2/features2d.hpp"
  #include "opencv2/highgui.hpp"
  #include "opencv2/calib3d.hpp"
  #include "opencv2/xfeatures2d.hpp"
  #include &lt;opencv2/nonfree/nonfree.hpp&gt;
  
  using namespace cv;
  using namespace cv::xfeatures2d;
  
  void readme();
  
  /** @function main */
  int main(int argc, char** argv)
  {
      if (argc != 3)
      {
          readme(); return -1;
      }
  
      Mat img_object = imread(argv[1], IMREAD_GRAYSCALE);
      Mat img_scene = imread(argv[2], IMREAD_GRAYSCALE);
  
      if (!img_object.data || !img_scene.data)
      {
          std::cout &lt;&lt; " --(!) Error reading images " &lt;&lt; std::endl; return -1;
      }
  
      //-- Step 1: Detect the keypoints using SURF Detector
      int minHessian = 400;
  
      Ptr&lt;SURF&gt; detector = SURF.create(minHessian);
  
      std::vector&lt;KeyPoint&gt; keypoints_object, keypoints_scene;
  
      detector.detect(img_object, keypoints_object);
      detector.detect(img_scene, keypoints_scene);
  
      //-- Step 2: Calculate descriptors (feature vectors)
      SurfDescriptorExtractor extractor;
  
      Mat descriptors_object, descriptors_scene;
  
      extractor.compute(img_object, keypoints_object, descriptors_object);
      extractor.compute(img_scene, keypoints_scene, descriptors_scene);
  
      //-- Step 3: Matching descriptor vectors using FLANN matcher
      FlannBasedMatcher matcher;
      std::vector&lt; DMatch &gt; matches;
      matcher.match(descriptors_object, descriptors_scene, matches);
  
      double max_dist = 0; double min_dist = 100;
  
      //-- Quick calculation of max and min distances between keypoints
      for (int i = 0; i &lt; descriptors_object.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 )
      std::vector&lt; DMatch &gt; good_matches;
  
      for (int i = 0; i &lt; descriptors_object.rows; i++)
      {
          if (matches[i].distance &lt; 3 * min_dist)
          {
              good_matches.push_back(matches[i]);
          }
      }
  
      Mat img_matches;
      drawMatches(img_object, keypoints_object, img_scene, keypoints_scene,
          good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
          std::vector&lt;char&gt;(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);
  
      //-- Localize the object
      std::vector&lt;Point2f&gt; obj;
      std::vector&lt;Point2f&gt; scene;
  
      for (int i = 0; i &lt; good_matches.size(); i++)
      {
          //-- Get the keypoints from the good matches
          obj.push_back(keypoints_object[good_matches[i].queryIdx].pt);
          scene.push_back(keypoints_scene[good_matches[i].trainIdx].pt);
      }
  
      Mat H = findHomography(obj, scene, RANSAC);
  
      //-- Get the corners from the image_1 ( the object to be "detected" )
      std::vector&lt;Point2f&gt; obj_corners(4);
      obj_corners[0] = cvPoint(0, 0); obj_corners[1] = cvPoint(img_object.cols, 0);
      obj_corners[2] = cvPoint(img_object.cols, img_object.rows); obj_corners[3] = cvPoint(0, img_object.rows);
      std::vector&lt;Point2f&gt; scene_corners(4);
  
      perspectiveTransform(obj_corners, scene_corners, H);
  
      //-- Draw lines between the corners (the mapped object in the scene - image_2 )
      line(img_matches, scene_corners[0] + Point2f(img_object.cols, 0), scene_corners[1] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
      line(img_matches, scene_corners[1] + Point2f(img_object.cols, 0), scene_corners[2] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
      line(img_matches, scene_corners[2] + Point2f(img_object.cols, 0), scene_corners[3] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
      line(img_matches, scene_corners[3] + Point2f(img_object.cols, 0), scene_corners[0] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
  
      //-- Show detected matches
      imshow("Good Matches &amp; Object detection", img_matches);
  
      waitKey(0);
      return 0;
  }
  
  /** @function readme */
  void readme()
  {
      std::cout &lt;&lt; " Usage: ./SURF_descriptor &lt;img1&gt; &lt;img2&gt;" &lt;&lt; std::endl;
  }
  </code></pre>
  
  <p>Errors:</p>
  
  <pre><code>1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(34): warning C4832: token '.' is illegal after UDT 'cv::xfeatures2d::SURF'
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(111) : see declaration of 'cv::xfeatures2d::SURF'
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(34): error C2275: 'cv::xfeatures2d::SURF' : illegal use of this type as an expression
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(111) : see declaration of 'cv::xfeatures2d::SURF'
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(34): error C2228: left of '.create' must have class/struct/union
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(38): error C2039: 'detect' : is not a member of 'cv::Ptr&lt;cv::xfeatures2d::SURF&gt;'
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(39): error C2039: 'detect' : is not a member of 'cv::Ptr&lt;cv::xfeatures2d::SURF&gt;'
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(42): error C2259: 'cv::xfeatures2d::SURF' : cannot instantiate abstract class
  1&gt;          due to following members:
  1&gt;          'void cv::xfeatures2d::SURF::setHessianThreshold(double)' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(127) : see declaration of 'cv::xfeatures2d::SURF::setHessianThreshold'
  1&gt;          'double cv::xfeatures2d::SURF::getHessianThreshold(void) const' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(128) : see declaration of 'cv::xfeatures2d::SURF::getHessianThreshold'
  1&gt;          'void cv::xfeatures2d::SURF::setNOctaves(int)' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(130) : see declaration of 'cv::xfeatures2d::SURF::setNOctaves'
  1&gt;          'int cv::xfeatures2d::SURF::getNOctaves(void) const' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(131) : see declaration of 'cv::xfeatures2d::SURF::getNOctaves'
  1&gt;          'void cv::xfeatures2d::SURF::setNOctaveLayers(int)' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(133) : see declaration of 'cv::xfeatures2d::SURF::setNOctaveLayers'
  1&gt;          'int cv::xfeatures2d::SURF::getNOctaveLayers(void) const' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(134) : see declaration of 'cv::xfeatures2d::SURF::getNOctaveLayers'
  1&gt;          'void cv::xfeatures2d::SURF::setExtended(bool)' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(136) : see declaration of 'cv::xfeatures2d::SURF::setExtended'
  1&gt;          'bool cv::xfeatures2d::SURF::getExtended(void) const' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(137) : see declaration of 'cv::xfeatures2d::SURF::getExtended'
  1&gt;          'void cv::xfeatures2d::SURF::setUpright(bool)' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(139) : see declaration of 'cv::xfeatures2d::SURF::setUpright'
  1&gt;          'bool cv::xfeatures2d::SURF::getUpright(void) const' : is abstract
  1&gt;          c:\users\belayachiry\documents\opencv\opencv\build\include\opencv2\nonfree\nonfree.hpp(140) : see declaration of 'cv::xfeatures2d::SURF::getUpright'
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(87): warning C4018: '&lt;' : signed/unsigned mismatch
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(105): warning C4244: 'argument' : conversion from 'int' to 'float', possible loss of data
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(105): error C3861: 'line': identifier not found
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(106): warning C4244: 'argument' : conversion from 'int' to 'float', possible loss of data
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(106): error C3861: 'line': identifier not found
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(107): warning C4244: 'argument' : conversion from 'int' to 'float', possible loss of data
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(107): error C3861: 'line': identifier not found
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(108): warning C4244: 'argument' : conversion from 'int' to 'float', possible loss of data
  1&gt;c:\users\belayachiry\documents\visual studio 2013\projects\imagewatch\imagewatch\source.cpp(108): error C3861: 'line': identifier not found
  </code></pre>