opencv

#include "opencv2/core/core.hpp"  
#include "opencv2/features2d/features2d.hpp"  
#include "opencv2/highgui/highgui.hpp"  
#include <opencv2/nonfree/nonfree.hpp>  
#include<opencv2/legacy/legacy.hpp>  
using namespace cv;  
  
  
int main( int argc, char** argv )  
{  
    Mat img_1 = imread( "a.jpg",CV_LOAD_IMAGE_GRAYSCALE );  
    Mat img_2 = imread( "b.jpg", CV_LOAD_IMAGE_GRAYSCALE );  
  
    if( !img_1.data || !img_2.data )  
    { return -1; }  
  
    //-- Step 1: Detect the keypoints using SURF Detector  
    int minHessian = 400;  
    SurfFeatureDetector detector( minHessian );  
    std::vector<KeyPoint> keypoints_1, keypoints_2;  
    detector.detect( img_1, keypoints_1 );  
    detector.detect( img_2, keypoints_2 );  
  
    //-- Step 2: Calculate descriptors (feature vectors)  
    SurfDescriptorExtractor extractor;  
    Mat descriptors_1, descriptors_2;  
    extractor.compute( img_1, keypoints_1, descriptors_1 ); 
    extractor.compute( img_2, keypoints_2, descriptors_2 );  
  
    //-- Step 3: Matching descriptor vectors with a brute force matcher  
    BruteForceMatcher< L2<float> > matcher;  
    std::vector< DMatch > matches;  
    matcher.match( descriptors_1, descriptors_2, matches );  
  
std::nth_element(matches.begin(),matches.begin()+24,matches.end());
    matches.erase(matches.begin()+25,matches.end());


//show matches
   for( size_t m = 0; m < matches.size(); m++ )
    {
int i1 =  matches[m].queryIdx;
            int i2 = matches[m].trainIdx;
std::cout<<"1......x:"<<matches[m].distance<<std::endl;
            assert(i1 >= 0 && i1 < static_cast<int>(keypoints_1.size()));
            assert(i2 >= 0 && i2 < static_cast<int>(keypoints_2.size()));
std::cout<<"1......x:"<<keypoints_1[i1].pt.x<<" y: "<<keypoints_1[i1].pt.y<<std::endl;
std::cout<<"2......x:"<<keypoints_2[i2].pt.x<<" y: "<<keypoints_2[i2].pt.y<<std::endl;
    }


    //-- Draw matches  
    Mat img_matches;
    drawMatches( img_1, keypoints_1, img_2, keypoints_2, matches, img_matches );  
    //-- Show detected matches  
    imshow("Matches", img_matches );  
    waitKey(0);
// draw matches
    return 0;  
}