从std :: vector< cv :: Point> :: const_iterator检索值

问题描述

我从图像中找到了轮廓.我想从轮廓中找到最小点和最小点.

I found a contour from an image. I want to find the min point and min point from the contours.

vector<Point> test = contours[0];
auto mmx = std::minmax_element(test.begin(), test.end(), less_by_y);

bool less_by_y(const cv::Point& lhs, const cv::Point& rhs)
{
    return lhs.y < rhs.y;
}

我已经尝试过这种编码，并且可以成功运行.但是由于我的愚蠢，我不知道如何从mmx检索数据.有人请帮助我吗?

I have tried this coding and it run successfully. But due to my stupidness, i do not know how to retrieve data from mmx. Anyone please help me?

如果我要从轮廓访问y点的值，该怎么做?我真的对那些数据类型感到困惑.

If i want to access the value of point y from contours, how to do it? I really confused with those data types.

推荐答案

您可以从 minmax_element 文档，它返回一对迭代器.

You can see from minmax_element documentation that it returns a pair of iterators.

给出:

vector<Point> pts = ...
auto mmx = std::minmax_element(pts.begin(), pts.end(), less_by_y);

您可以使用mmx.first访问min元素的迭代器，并使用mmx.second访问max元素的迭代器.

you can access the iterator to the min element with mmx.first, and the iterator to the max element with mmx.second.

如果要检索最小和最大y值，则需要执行以下操作:

If you want to retrieve the min and max y values you need to do:

int min_y = mmx.first->y;
int max_y = mmx.second->y;

---

由于您使用的是OpenCV，因此还可以使用boudingRect查找y值:

---

Since you are in OpenCV, you can also find the y values using boudingRect:

Rect box = boundingRect(pts);
std::cout << "min y: " << box.tl().y << std::endl;
std::cout << "max y: " << box.br().y - 1 << std::endl; // Note the -1!!!

尽管这可能会慢一些，但您无需定义自定义比较功能.如果需要，这还将计算最小值和最大值x.

Although this is probably slower, you don't need to define the custom comparison function. This computes also min and max x, if needed.

下面是一个完整的示例:

Here a complete example:

#include <opencv2/opencv.hpp>
#include <algorithm>
#include <iostream>
using namespace cv;

bool less_by_y(const cv::Point& lhs, const cv::Point& rhs)
{
    return lhs.y < rhs.y;
}

int main(int argc, char** argv)
{
    // Some points
    vector<Point> pts = {Point(5,5), Point(5,0), Point(3,5), Point(3,7)};

    // Find min and max "y"
    auto mmx = std::minmax_element(pts.begin(), pts.end(), less_by_y);

    // Get the values
    int min_y = mmx.first->y;
    int max_y = mmx.second->y;

    // Get the indices in the vector, if needed
    int idx_min_y = std::distance(pts.begin(), mmx.first);
    int idx_max_y = std::distance(pts.begin(), mmx.second);

    // Show results
    std::cout << "min y: " << min_y << " at index: " << idx_min_y << std::endl;
    std::cout << "max y: " << max_y << " at index: " << idx_max_y << std::endl;

    // Using OpenCV boundingRect

    Rect box = boundingRect(pts);
    std::cout << "min y: " << box.tl().y << std::endl;
    std::cout << "max y: " << box.br().y - 1 << std::endl; // Note the -1!!!

    return 0;
}

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