How to use cv::matchShapes method from coding point of view in c or c++

edit

Hi all, My objective is to find the pattern in the image captured from camera for this I found the cv::matchShapes method of opencv to implement it.

When I have implemented this method it is making the app crash on matchShapes method.Might be I have done something wrong:-

I exactly do not know how to use this method in order to find the match shape in my query image.This is what I tried.

Please help me in providing some code that can run properly.

Here is my code:-

    - (std::vector<std::vector<cv::Point> >)tryingMatchShapes:(cv::Mat)_image _image1:(cv::Mat)_image1
    {
        std::vector<std::vector<cv::Point> > squares;

        cv::Mat pyr, timg, gray0(_image.size(), CV_8U), gray;
        int thresh = 50, N = 11;
        cv::pyrDown(_image, pyr, cv::Size(_image.cols/2, _image.rows/2));
        cv::pyrUp(pyr, timg, _image.size());
        std::vector<std::vector<cv::Point> > contours;
        for( int c = 0; c < 3; c++ ) {
            int ch[] = {c, 0};
            mixChannels(&timg, 1, &gray0, 1, ch, 1);
            for( int l = 0; l < N; l++ ) {
                if( l == 0 ) {
                    cv::Canny(gray0, gray, 0, thresh, 5);
                    cv::dilate(gray, gray, cv::Mat(), cv::Point(-1,-1));
                }
                else {
                    gray = gray0 >= (l+1)*255/N;
                }
                cv::findContours(gray, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);

            }
        }
                cv::Mat pyr1, timg1, gray2(_image1.size(), CV_8U), gray1;
                cv::pyrDown(_image1, pyr1, cv::Size(_image1.cols/2, _image1.rows/2));
                cv::pyrUp(pyr1, timg1, _image1.size());
                std::vector<std::vector<cv::Point> > contours1;
                for( int c = 0; c < 3; c++ ) {
                    int ch[] = {c, 0};
                    mixChannels(&timg1, 1, &gray2, 1, ch, 1);
                    for( int l = 0; l < N; l++ ) {
                        if( l == 0 ) {
                            cv::Canny(gray2, gray1, 0, thresh, 5);
                            cv::dilate(gray1, gray1, cv::Mat(), cv::Point(-1,-1));
                        }
                        else {
                            gray1 = gray2 >= (l+1)*255/N;
                        }
                        cv::findContours(gray1, contours1, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);



                    }
                }
for( size_t i = 0; i < contours.size(); i++ )
    {
  double value=  cv::matchShapes(contours[i], contours1[i], CV_CONTOURS_MATCH_I1, 0);
        NSLog(@"%f",value);
    }  
   return squares;
    }


    UIImage *testImage = [UIImage imageNamed:@"note_with_marks (1).png"];    
    [self.imageView setImage:testImage];
    cv::Mat forground = [testImage CVMat]; 
    UIImage *testImage2 = [UIImage imageNamed:@"1.png"];    
    cv::Mat forground2 = [testImage2 CVMat];
    [self tryingMatchShapes:forground _image1:forground2];


    Error:-

    OpenCV Error: Assertion failed (contour1.checkVector(2) >= 0 && contour2.checkVector(2) >= 0 && (contour1.depth() == CV_32F || contour1.depth() == CV_32S) && contour1.depth() == contour2.depth()) in matchShapes, file /Users/Aziz/Documents/Projects/opencv_sources/trunk/modules/imgproc/src/contours.cpp, line 1705

I am sure I am doing something wrong in the code but exactly what that I am not able to figure out.

Please some body help me in implementing this method from coding point of view. Please I need some coding help.I have already gone through I lot of theoretical concepts.

Thanks in advance!