#include <opencv2/imgproc.hpp>
void cv::approxPolyDP(InputArray curve, OutputArray approxCurve, double epsilon, bool closed);

1. The function reads the input points from curve.
2. It computes a simplified polygon according to the Douglas–Peucker algorithm.
3. It writes new points into approxCurve.

Those points are newly created cv::Point / cv::Point2f objects. Modifying the result polygon does not modify the original.

std::vector<cv::Point2f> pts2d;
cv::RotatedRect rect = cv::minAreaRect(pts2d);
cv::Point2f corners2d[4];
rect.points(corners2d); // order is arbitrary but consistent

cv::Point2f center2d = rect.center;

// Orientation angle in radians (OpenCV angle in degrees)
float angle_rad = rect.angle * static_cast<float>(CV_PI) / 180.0f;