opencv将坐标点按逆时针顺序存放

布满荆棘的人生 2023-06-10 05:21 18阅读 0赞

### opencv将坐标点按逆时针顺序存放 ###

在做项目的时候有时需要对轮廓点按照顺时针或者逆时针存储，假设坐标点保存的数据类型是`vector<Point>`，现在将其按照逆时针的顺序存放，废话不多说，直接上函数。

#include<iostream>
    #include <opencv2\opencv.hpp>
    
    using namespace cv;
    using namespace std;
    
    //若点a大于点b,即点a在点b顺时针方向,返回false,否则返回true
    bool PointCmp(Point a, Point b, Point center)
    {
        
        if (a.x >= 0 && b.x < 0)
            return false;
        if (a.x == 0 && b.x == 0)
            return a.y < b.y;
        int det = ((a.x - center.x) * (b.y - center.y) - (b.x - center.x) * (a.y - center.y));
        if (det < 0)
            return false;
        if (det > 0)
            return true;
        double d1 = (a.x - center.x) * (a.x - center.x) + (a.y - center.y) * (a.y - center.y);
        double d2 = (b.x - center.x) * (b.x - center.y) + (b.y - center.y) * (b.y - center.y);
        return d1 < d2;
    } 
    
    void ClockwiseSortPoints(vector<Point> &vPoints)
    {
        
        //计算重心
        Point center;
        double X = 0, Y = 0;
        for (int i = 0; i < vPoints.size(); i++)
        {
        
            X += vPoints[i].x;
            Y += vPoints[i].y;
        }
        center.x = (int)X / vPoints.size();
        center.y = (int)Y / vPoints.size();
        //冒泡排序
        for (int i = 0; i < vPoints.size() - 1; i++)
        {
        
            for (int j = 0; j < vPoints.size() - i - 1; j++)
            {
        
                if (PointCmp(vPoints[j], vPoints[j + 1], center))
                {
        
                    Point tmp = vPoints[j];
                    vPoints[j] = vPoints[j + 1];
                    vPoints[j + 1] = tmp;
                }
            }
        }
    }
    vector<Point> findBiggestContour(Mat binary_image)
    {
        
    	vector<vector<cv::Point>> contours;
    	vector<Vec4i> hierarchy;
    
    	int largest_area = 0;
    	int largest_contour_index = 0;
    	findContours(binary_image, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
    	for (int i = 0; i < contours.size(); i++) // iterate through each contour. 
    	{
        
    		double a = contourArea(contours[i], false);  //  Find the area of contour
    		if (a > largest_area) {
        
    			largest_area = a;
    			largest_contour_index = i;                //Store the index of largest contour
    		}
    	}
    	return contours[largest_contour_index];
    }
    int main()
    {
        
    	Mat img = imread("25.png", 0);
    	threshold(img, img, 127, 255, CV_THRESH_BINARY);
    	vector<Point> bigestContour;
    	bigestContour = findBiggestContour(img);//提取最大轮廓
    	ClockwiseSortPoints(bigestContour);
    	for(int i = 0; i < bigestContour.size(); i++)
    	{
        
    		cout<<"第"<<i<<"个轮廓点坐标："<<bigestContour[i].x,bigestContour[i].y<<endl;
    	}	
    	return 0;
    }

这里说明一下，其实轮廓本身已经是逆时针方向了，因为使用了宏CV\_CHAIN\_APPROX\_NONE，但如果不使用这个宏，就有必要对轮廓排序了，除了对轮廓点可以采用此方法排序外，还可以对凸多边形点进行排序，这样在项目中可以有效的处理我们的数据，平时写博客少，有问题可以沟通，qq385105501。