Finding extreme points in contours with OpenCV C++

Question

I have tried to implement this code , but I have a trouble when I want to determine the most extreme point of the contour follow this tutorial.

# determine the most extreme points along the contour
    extLeft = tuple(c[c[:, :, 0].argmin()][0])
    extRight = tuple(c[c[:, :, 0].argmax()][0])
    extTop = tuple(c[c[:, :, 1].argmin()][0])
    extBot = tuple(c[c[:, :, 1].argmax()][0])

Can anyone help me to solve this problem?

Answer 1

Starting from a std::vector<cv::Point> , you can use std::max_element and std::min_element with an appropriate comparator, that works on x coordinates to find left and right points, and works on y coordinates to find top and bottom points:

// Your points
vector<Point> pts;
...


Point extLeft  = *min_element(pts.begin(), pts.end(), 
                      [](const Point& lhs, const Point& rhs) {
                          return lhs.x < rhs.x;
                  }); 
Point extRight = *max_element(pts.begin(), pts.end(),
                      [](const Point& lhs, const Point& rhs) {
                          return lhs.x < rhs.x;
                  });
Point extTop   = *min_element(pts.begin(), pts.end(), 
                      [](const Point& lhs, const Point& rhs) {
                          return lhs.y < rhs.y;
                  }); 
Point extBot   = *max_element(pts.begin(), pts.end(),
                      [](const Point& lhs, const Point& rhs) {
                          return lhs.y < rhs.y;
                  });