arcLength函数[通俗易懂]

1、arcLength函数

函数的作用

主要是计算图像轮廓的周长、

2、函数调用形式

C++: double arcLength(InputArray curve, bool closed)

参数详解：

InputArray curve：表示图像的轮廓

bool closed：表示轮廓是否封闭的

3、一般图像轮廓矩也可以算出图像的周长和面积

opencv代码：

   
   
   

    
    
 
     
 
      
 
     
 
     
 
      
 
       #include “opencv2/highgui/highgui.hpp” 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       #include “opencv2/imgproc/imgproc.hpp” 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       #include <iostream> 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       #include <stdio.h> 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       #include <stdlib.h> 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       using 
       namespace cv; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       using 
       namespace 
       std; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        Mat src; Mat src_gray; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       int thresh = 
       100; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       int max_thresh = 
       255; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       RNG rng(12345); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 函数声明 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       void thresh_callback(int, void* ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /** @主函数 */ 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       int main( int argc, char** argv ) 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        { 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 读入原图像, 返回3通道图像数据 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        src = imread( argv[ 
       1], 
       1 ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 把原图像转化成灰度图像并进行平滑 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        cvtColor( src, src_gray, CV_BGR2GRAY ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        blur( src_gray, src_gray, Size( 
       3, 
       3) ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 创建新窗口 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       char* source_window = 
       “Source”; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        namedWindow( source_window, CV_WINDOW_AUTOSIZE ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        imshow( source_window, src ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        createTrackbar( 
       ” Canny thresh:”, 
       “Source”, &thresh, max_thresh, thresh_callback ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        thresh_callback( 
       0, 
       0 ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        waitKey( 
       0); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       return( 
       0); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        } 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /** @thresh_callback 函数 */ 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       void thresh_callback(int, void* ) 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        { 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        Mat canny_output; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       vector< 
       vector<Point> > contours; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       vector<Vec4i> hierarchy; 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 使用Canndy检测边缘 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        Canny( src_gray, canny_output, thresh, thresh* 
       2, 
       3 ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 找到轮廓 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point( 
       0, 
       0) ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 计算矩 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       vector<Moments> mu(contours.size() ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       for( 
       int i = 
       0; i < contours.size(); i++ ) 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        { mu[i] = moments( contours[i], 
       false ); } 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 计算中心矩: 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       vector<Point2f> mc( contours.size() ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       for( 
       int i = 
       0; i < contours.size(); i++ ) 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        { mc[i] = Point2f( mu[i].m10/mu[i].m00 , mu[i].m01/mu[i].m00 ); } 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 绘制轮廓 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       for( 
       int i = 
       0; i< contours.size(); i++ ) 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        { 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        Scalar color = Scalar( rng.uniform( 
       0, 
       255), rng.uniform( 
       0, 
       255), rng.uniform( 
       0, 
       255) ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        drawContours( drawing, contours, i, color, 
       2, 
       8, hierarchy, 
       0, Point() ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        circle( drawing, mc[i], 
       4, color, 
       -1, 
       8, 
       0 ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        } 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 显示到窗口中 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        namedWindow( 
       “Contours”, CV_WINDOW_AUTOSIZE ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        imshow( 
       “Contours”, drawing ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       /// 通过m00计算轮廓面积并且和OpenCV函数比较 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       printf( 
       “\t Info: Area and Contour Length \n”); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       for( 
       int i = 
       0; i< contours.size(); i++ ) 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        { 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      
 
       printf( 
       ” * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f \n”, i, mu[i].m00, contourArea(contours[i]), arcLength( contours[i], 
       true ) ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        Scalar color = Scalar( rng.uniform( 
       0, 
       255), rng.uniform( 
       0, 
       255), rng.uniform( 
       0, 
       255) ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        drawContours( drawing, contours, i, color, 
       2, 
       8, hierarchy, 
       0, Point() ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        circle( drawing, mc[i], 
       4, color, 
       -1, 
       8, 
       0 ); 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        } 
      
 
     
    
    
 
     
 
      
 
     
 
     
 
      

        }