find large contour & calculate center of gravity sample code using OpenCV2

find_large_contour_center_of_gravity.cpp

bool find_large_contour_center_of_gravity(cv::Mat &src_img, cv::Point &result)
{
	cv::Mat gray_img, bin_img, erode_img, dilate_img;
	std::vector<std::vector<cv::Point> > contours;
	int max_area = 0;
	std::vector<cv::Point> large_contour;
	std::vector<cv::Point> convex_hull;
	
	// convert to grayscale
	cv::cvtColor(src_img, gray_img, CV_BGR2GRAY);
	
	// convert to binary image
	cv::threshold(gray_img, bin_img, 0, 255, cv::THRESH_BINARY|cv::THRESH_OTSU);

	// remove noise
	cv::erode(bin_img, erode_img, cv::Mat());
	cv::erode(erode_img, erode_img, cv::Mat());
	cv::dilate(erode_img, dilate_img, cv::Mat());
	cv::dilate(dilate_img, dilate_img, cv::Mat());
	
	// find contours
	cv::findContours(dilate_img, contours, CV_RETR_LIST,CV_CHAIN_APPROX_SIMPLE);
	if (contours.size() == 0) return false;
	
	// find max area contours
	for (unsigned int i = 0; i < contours.size(); ++i) {
		int area = (int)cv::contourArea(contours[i]);
		if (area > max_area) {
			large_contour = contours[i];
			max_area = area;
		}
	}
	if (max_area == 0) return false;
	
	// simplify large contours
	cv::approxPolyDP(cv::Mat(large_contour), large_contour, 5, true);
	
	// convex hull
	cv::convexHull(large_contour, convex_hull, false);
	if (convex_hull.size() < 3 ) return false;
	
	// center of gravity
	cv::Moments mo = cv::moments(convex_hull);
	result = cv::Point(mo.m10/mo.m00 , mo.m01/mo.m00);
	
	return true;
}