How to calculate the rotation Angle difference between similarity contours

C++
1

https://i.stack.imgur.com/E5Vbj.png. After obtaining the contour data of the picture and the similarity value between the contours, At present not found the method to calculate the rotation Angle difference between similarity contours.

int main(int argc,char* argv[])
{
    cout<< "params count :"<<argc<<endl;
    cout<< "params value are :";
    for (int i = 0; i < argc; i++) {
        printf(" [%d]: %s",i,argv[i]);
    }

    if (argc > 1){

        Mat src1 = imread(argv[1]);
        imshow(" src1 ",src1);
        cout<<" src1 channels: "<<src1.channels()<<endl;
       

        Mat grayImage;
        if(src1.channels() > 1){
            cvtColor(src1,grayImage,COLOR_BGR2GRAY);
        }else {
            grayImage = src1;
        }

        Mat threshodImage1;
        threshold(grayImage, threshodImage1, 128, 255, THRESH_BINARY|THRESH_OTSU); // | 

        vector<Vec4i> hierarchy;
        vector<vector<Point> > contours;

        findContours(threshodImage1,contours,hierarchy,RETR_EXTERNAL,CHAIN_APPROX_SIMPLE);
        cout<< " contours size :" << contours.size() <<endl;

        RotatedRect rRect;
        Moments shapeMoments;
        double shapeHumoments[7];
        Point centerofmass;

        RotatedRect _minAreaRect;

        Mat resImage = Mat::zeros(threshodImage1.size(),CV_8UC3);
        for(size_t i=0; i<contours.size(); i++){

            double area = contourArea(contours[i]);
            shapeMoments = moments(contours[i]);
            HuMoments(shapeMoments,shapeHumoments);
            rRect = cv::minAreaRect(contours[i]);

            centerofmass.x = (shapeMoments.m10 / shapeMoments.m00);
            centerofmass.y = (shapeMoments.m01 / shapeMoments.m00);

             for (size_t j = i+1; j< contours.size(); j++){
                 double match = matchShapes(contours[i],contours[j],1,0.0);
                 cout << i+1  << " VS " << j+1 << "   match:" <<match << endl ;
             }

        }

        imshow("resImage",resImage);
        waitKey(1000);

    }
   
    return 0;
}