Draw lines connecting centroids of objects using OpenCV - opencv

Question

I have found out the centroid of multiple objects in my image using the code provided here OpenCV examples
Here is the code which found the centroid and stored them in a vector.
cv::Mat InputImage;
cv::Mat CannyOutput;
vector<vector<cv::Point> > contours;
vector<Vec4i> hierarchy;
RNG rng(12345);
InputImage = cv::imread("Untitled.jpg");
//Edge detection
Canny(InputImage, CannyOutput, 100, 150);
//Contour detection
cv::findContours(CannyOutput, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, cv::Point(0, 0));
//Finding Moments
vector<Moments> mu(contours.size());
for (int i = 0; i < contours.size(); i++)
{
mu[i] = moments(contours[i], false);
}
//Calculating Centroid
vector<Point2f> mc(contours.size());
for (int i = 0; i < contours.size(); i++)
{
mc[i] = Point2f(mu[i].m10 / mu[i].m00, mu[i].m01 / mu[i].m00);
}
// Drawing
Mat drawing = Mat::zeros(CannyOutput.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));
//Drawing contour
drawContours(drawing, contours, i, color, 2, 8, hierarchy, 0, cv::Point());
//Drawing circles with centroid as centre
circle(drawing, mc[i], 4, color, -1, 8, 0);
}
What I want to do is draw a polygon with the centroid as the vertices. I used drawcontours, polyline and line functions but not getting the desired result. Is there a way to achieve this? . I need it to be achieved in C++
Output image
Desired image
Also, on another note, the code doesnt seem to be displaying the centroid if am replacing the 'color' variable with BGR value. Seems like both contour and centroid has to be of same color if i want to see the centroid. When i gave (0,255,255) for contour and (255,255,0) for centroid, the centroid was not displaying .

Answer 1

For the given sample image, you can use convexhull to obtain the order of centers, and then draw them with polylines.