OpenCV: найти соотношение площади пересечения двух фигур до их обьединения

#include "pch.h"
#include <opencv2/opencv.hpp>
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
 
using namespace cv;
using namespace std;
 
Mat src; 
Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);
 
/// Function header
void thresh_callback(int, void*);
 
/** @function main */
int main()
{
    const char* imagename = "vib1.jpg";
    /// Load source image and convert it to gray
    src = imread(imagename, 1);
 
    /// Convert image to gray and blur it
    cvtColor(src, src_gray, COLOR_BGR2GRAY);
    blur(src_gray, src_gray, Size(3, 3));
 
    /// Create Window
    const char* source_window = "Source";
    namedWindow(source_window, WINDOW_NORMAL);
    resizeWindow(source_window, 600, 600);
    imshow(source_window, src);
 
    createTrackbar(" Canny thresh:", "Source", &thresh, max_thresh, thresh_callback);
    thresh_callback(0, 0);
 
    waitKey(0);
    return(0);
}
 
/** @function thresh_callback */
void thresh_callback(int, void*)
{
    Mat canny_output;
    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;
 
    /// Detect edges using canny
    Canny(src_gray, canny_output, thresh, thresh * 3, 3);
    /// Find contours
    findContours(canny_output, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
 
    /// Draw contours
    Mat drawing = Mat::zeros(canny_output.size(), CV_8UC3);
    for (int i = 0; i < contours.size(); i++)
    {
        Scalar color = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255));
        drawContours(drawing, contours, i, color, 4, 8, hierarchy, 0, Point());
    }
 
    /// Show in a window
    namedWindow("Contours", WINDOW_NORMAL);
    resizeWindow("Contours", 600, 600);
    imshow("Contours", drawing);
}