Get the each coodinates of all corner of 2 rectangle

edit

i hope the code below helps you.

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"

using namespace cv;

int main()
{

    Mat src = Mat::zeros( 400, 400, CV_8UC3);

    Rect r(100,100,50,50);

    Point point0 = Point(r.x, r.y);
    Point point1 = Point(r.x + r.width, r.y);
    Point point2 = Point(r.x + r.width, r.y + r.height);
    Point point3 = Point(r.x, r.y + r.height);

    rectangle( src, r, Scalar::all(255));

    circle( src, point0, 10, Scalar( 0, 0, 255) );
    circle( src, point1, 10, Scalar( 0, 0, 255) );
    circle( src, point2, 10, Scalar( 0, 0, 255) );
    circle( src, point3, 10, Scalar( 0, 0, 255) );

    imshow( "coodinates of all corner of rectangle", src );
    waitKey();

    return 0;
}