Store the centroid to a new array or vector - c++

Question

This is the image
This is the code below
#include "opencv2/opencv.hpp"
using namespace cv;
using namespace std;
int main(int argc, char** argv)
{
// Read image
Mat im = imread("beethoven_ode_to_joy.jpg", IMREAD_GRAYSCALE);
// Setup SimpleBlobDetector parameters.
SimpleBlobDetector::Params params;
// Change thresholds
params.minThreshold = 10;
params.maxThreshold = 200;
// Filter by Area.
params.filterByArea = true;
params.minArea = 15;
// Filter by Circularity
params.filterByCircularity = true;
params.minCircularity = 0.1;
// Filter by Convexity
params.filterByConvexity = true;
params.minConvexity = 0.01;
// Filter by Inertia
params.filterByInertia = true;
params.minInertiaRatio = 0.01;
// Storage for blobs
vector<KeyPoint> keypoints;
// Set up detector with params
SimpleBlobDetector detector(params);
// Detect blobs
detector.detect(im, keypoints);
At this portion of the code is printing all the centroid of the blob, but i need to store the centroid of the blob into a new vector
for (vector<KeyPoint>::iterator it = keypoints.begin(); it != keypoints.end(); ++it)
{
KeyPoint k = *it;
cout << k.pt << endl;
}
// Draw detected blobs as red circles.
// DrawMatchesFlags::DRAW_RICH_KEYPOINTS flag ensures
// the size of the circle corresponds to the size of blob
Mat im_with_keypoints;
drawKeypoints(im, keypoints, im_with_keypoints, Scalar(0, 0, 255), DrawMatchesFlags::DRAW_RICH_KEYPOINTS);
// Show blobs
imshow("keypoints", im_with_keypoints);
imwrite("a.jpg", im_with_keypoints);
waitKey(0);
}

Answer 1

Instead of:
for (vector<KeyPoint>::iterator it = keypoints.begin(); it != keypoints.end(); ++it)
{
KeyPoint k = *it;
cout << k.pt << endl;
}
You can do this:
std::vector<decltype(keypoints[0].pt)> vector_of_points;
keypoints.reserve(keypoints.size());
for (vector<KeyPoint>::iterator it = keypoints.begin(); it != keypoints.end(); ++it)
{
KeyPoint k = *it;
cout << k.pt << endl;
vector_of_points.emplace_back(k.pt);
}
Or even better:
std::vector<decltype(keypoints[0].pt)> vector_of_points(keypoints.size());
std::transform(std::begin(keypoints),std::end(keypoints),std::begin(vector_of_points),[](KeyPoint const& item){std::cout<<item.pt;return item.pt;});
EDIT:
If you want to access the centriod you can do this:
for(auto& centr:vector_of_points){
//centr is the centriod
}
If you want a specific centroid. The fourth for example:
vector_of_points[4]