opencv C++
輪郭線までは出せているのですが、その輪郭線を円や四角で囲む方法がわかりません

    #include"stdafx.h"
    #include<vector>
    #include<strstream>

    void run()
    {
        cv::Mat image;

        //メインループ


        while (1) {
       //グレースケール入力
        cv::Mat src = cv::imread("/*任意の２値画像*/", cv::IMREAD_GRAYSCALE);

       // モルフォロジー処理
                cv::Mat opening;
                cv::Mat kernel(3, 3, CV_8U, cv::Scalar(1));
                cv::morphologyEx(thresh, opening, cv::MORPH_OPEN, kernel, cv::Point(-1, -1), 2);
                //cv::imshow("モルフォロジー処理化", opening);

                // 背景領域抽出
                cv::Mat sure_bg;
                cv::dilate(opening, sure_bg, kernel, cv::Point(-1, -1), 3);

                // 前景領域抽出
                cv::Mat dist_transform;
                cv::distanceTransform(opening, dist_transform, CV_DIST_L2, 5);  //輪郭から距離が離れるほど濃くする
                cv::Mat sure_fg;
                double minVal, maxVal;
                cv::Point minLoc, maxLoc;
                cv::minMaxLoc(dist_transform, &minVal, &maxVal, &minLoc, &maxLoc);
                cv::threshold(dist_transform, sure_fg, 0.2*maxVal, 255, 0);
                dist_transform = dist_transform / maxVal;

                // 不明領域抽出
                cv::Mat unknown, sure_fg_uc1;
                sure_fg.convertTo(sure_fg_uc1, CV_8UC1);
                cv::subtract(sure_bg, sure_fg_uc1, unknown);

                // 前景ラベリング
                using namespace std;

                int compCount = 0;
                vector<vector<cv::Point> > contours;
                vector<cv::Vec4i> hierarchy;
                sure_fg.convertTo(sure_fg, CV_32SC1, 1.0);
                cv::findContours(sure_fg, contours, hierarchy, cv::RETR_CCOMP, cv::CHAIN_APPROX_SIMPLE);
                if (contours.empty()) return;
                cv::Mat markers = cv::Mat::zeros(sure_fg.rows, sure_fg.cols, CV_32SC1);
                int idx = 0;
                for (; idx >= 0; idx = hierarchy[idx][0], compCount++)
                    cv::drawContours(markers, contours, idx, cv::Scalar::all(compCount + 1), -1, 8, hierarchy, INT_MAX);
                markers = markers + 1;

                // 不明領域は今のところゼロ
                for (int i = 0; i<markers.rows; i++) {
                    for (int j = 0; j<markers.cols; j++) {
                        unsigned char &v = unknown.at<unsigned char>(i, j);
                        if (v == 255) {
                            markers.at<int>(i, j) = 0;
                        }

                    }

                }
                watershed(hsv, markers);
                cv::Mat wshed(markers.size(), CV_8UC3);
                vector<cv::Vec3b> colorTab;
                for (int i = 0; i < compCount; i++)
                {
                    int b = cv::theRNG().uniform(0, 255);
                    int g = cv::theRNG().uniform(0, 255);
                    int r = cv::theRNG().uniform(0, 255);
                    colorTab.push_back(cv::Vec3b((uchar)b, (uchar)g, (uchar)r));
                }

                // paint the watershed image
                for (int i = 0; i < markers.rows; i++) {
                    for (int j = 0; j < markers.cols; j++)
                    {
                        int index = markers.at<int>(i, j);
                        if (index == -1)
                            wshed.at<cv::Vec3b>(i, j) = cv::Vec3b(255, 255, 255);
                        else if (index <= 0 || index > compCount)
                            wshed.at<cv::Vec3b>(i, j) = cv::Vec3b(0, 0, 0);
                        else
                            wshed.at<cv::Vec3b>(i, j) = colorTab[index - 1];
                    }
                }
                cv::Mat imgG;
                cvtColor(gray, imgG, cv::COLOR_GRAY2BGR);
                wshed = wshed * 0.5 + imgG * 0.5;
                              }
        }