text: #include "opencv2/opencv_modules.hpp"
  #include <stdio.h>
  
  #ifndef HAVE_OPENCV_NONFREE
  
  int main(int, char**)
  {
      printf("The sample requires nonfree module that is not available in your OpenCV distribution.\n");
      return -1;
  }
  
  #else
  
  # include "opencv2/core/core.hpp"
  # include "opencv2/features2d/features2d.hpp"
  # include "opencv2/highgui/highgui.hpp"
  # include "opencv2/nonfree/nonfree.hpp"
  
  using namespace cv;
  
  static void help()
  {
      printf("\nThis program demonstrates using features2d detector, descriptor extractor and simple matcher\n"
              "Using the SURF desriptor:\n"
              "\n"
              "Usage:\n matcher_simple <image1> <image2>\n");
  }
  
  int main(int argc, char** argv)
  {
      if(argc != 3)
      {
          help();
          return -1;
      }
  
      Mat img1 = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
      Mat img2 = imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE);
      if(img1.empty() || img2.empty())
      {
          printf("Can't read one of the images\n");
          return -1;
      }
  
      // detecting keypoints
      SurfFeatureDetector detector(400);
      vector<KeyPoint> keypoints1, keypoints2;
      detector.detect(img1, keypoints1);
      detector.detect(img2, keypoints2);
  
      // computing descriptors
      SurfDescriptorExtractor extractor;
      Mat descriptors1, descriptors2;
      extractor.compute(img1, keypoints1, descriptors1);
      extractor.compute(img2, keypoints2, descriptors2);
  
      // matching descriptors
      BFMatcher matcher(NORM_L2);
      vector<DMatch> matches;
      matcher.match(descriptors1, descriptors2, matches);
  
      // drawing the results
      namedWindow("matches", 1);
      Mat img_matches;
      drawMatches(img1, keypoints1, img2, keypoints2, matches, img_matches);
      imshow("matches", img_matches);
      waitKey(0);
  
      return 0;
  }
  
  #endif
  