c++ - Best fit a circle from a binary image using contours or any other technique -

i've have binary image computed algorithms. there hole in image , want best fit circle in hole. tried using bestminenclosingcircle function don't give best results.

here binary image

here function

here expected

i want exclude part

here code finding contours

    vector<vec4i> hierarchy;     vector<vector<point> > contours;       findcontours(src, contours, hierarchy, retr_tree, chain_approx_simple, point(0, 0)); 

check code below

#include "opencv2/imgcodecs.hpp" #include "opencv2/highgui.hpp" #include "opencv2/imgproc.hpp" #include <iostream>  using namespace cv; using namespace std;   int main(int, char** argv) {     mat src, src_gray;      /// load source image , convert gray     src = imread("e:/test/iffz9.png");     resize(src, src, size(), 0.25, 0.25);      /// convert image gray , blur     cvtcolor(src, src_gray, color_bgr2gray);     blur(src_gray, src_gray, size(3, 3));      imshow("source", src);      mat threshold_output;     vector<vector<point> > contours;      /// detect edges using threshold     threshold(src_gray, threshold_output, 127, 255, thresh_binary);     /// find contours     findcontours(threshold_output, contours, retr_tree, chain_approx_simple);      (size_t = 0; < contours.size(); i++)     {         if (contours[i].size() > 50)         {             rotatedrect minellipse = fitellipse(contours[i]);              int size = min(minellipse.size.width, minellipse.size.height) / 2;             // ellipse             if (size < src.rows / 2)                 ellipse(src, minellipse.center, size(size, size), 0, 360, 0, scalar(0, 0, 0255), 2, 8);         }     }      imshow("contours", src);     waitkey(0);      return 0; }