opencv sift match

#include "opencvlib.h"using namespace cv;int main(){    Mat img_1 = cv::imread("1.png");    Mat img_2 = cv::imread("2.png");    imshow("img1", img_1);    imshow("img2", img_2);    if (!img_1.data || !img_2.data)    {        std::cout << " --(!) Error reading images " << std::endl; 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)    SiftDescriptorExtractor extractor;    //SurfDescriptorExtractor    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 using FLANN matcher    FlannBasedMatcher matcher;    std::vector< DMatch > matches;    matcher.match(descriptors_1, descriptors_2, matches);    double max_dist = 0; double min_dist = 1000;    //-- Quick calculation of max and min distances between keypoints    for (int i = 0; i < descriptors_1.rows; i++)    {        double dist = matches[i].distance;        if (dist < min_dist) min_dist = dist;        if (dist > 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 2*min_dist )    //-- PS.- radiusMatch can also be used here.    std::vector< DMatch > good_matches;    for (int i = 0; i < descriptors_1.rows; i++)    {        if (matches[i].distance < 2 * min_dist)        {            good_matches.push_back(matches[i]);        }    }    //-- Draw only "good" matches    Mat img_matches;    drawMatches(img_1, keypoints_1, img_2, keypoints_2,        good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),        vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);    //-- Show detected matches    imshow("Good Matches", img_matches);    imwrite("matchs.jpg", img_matches);    for (int i = 0; i < good_matches.size(); i++)    {        printf("-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  \n", i, good_matches[i].queryIdx, good_matches[i].trainIdx);    }    waitKey(0);    system("pause");    return 0;}

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