多边形包围轮廓

1、矩形函数

Rect boundingRect(InputArray Points)

输入二维点集，可以输vector或Mat

返回外部矩形边界

2、寻找可旋转最小包围矩形

RotatedRect minAreaRect(InputArray points)

输入二维点集，可以输vector或Mat

3、寻找最小包围圆形

void minEnclosingCircle(InputArray points,Point2f &center,float radius)

参数一：输入二维点集，可以是vector或Mat类型

参数二：输出圆的中心

参数三：输出圆的半径

4、椭圆拟合二维点集

RotatedRect fitEllipse(InputArray points)

输入二维点集，可以输vector或Mat

5、逼近多边形曲线

void approxPloyDP(InputArray curve,OutputArray approxCurve,double epllison,bool closed)

参数一：输入二维点集，可以输vector或Mat

参数二：多边形逼近结果，其类型与参数一一致

参数三：逼近精度，为原始曲线和近似曲线的最大值

参数四：为真则为封闭曲线，为假则为不封闭曲线

示例：

#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#define WINDOW_NAME1 "【原始图】"
#define WINDOW_NAME2 "【效果图】"
using namespace std;
using namespace cv;

Mat g_srcImage;
Mat g_grayImage;
int g_nThresh=50;
int g_nMaxThresh=255;
RNG g_rng(12345);
void on_ContoursChange(int,void *);
int main(int argc,char *argv[])
{
	if(argc!=2)
	{
		cout<<"input error"<<endl;
		return -1;
	}
	g_srcImage = imread(argv[1]);
	if(g_srcImage.empty())
	{
		cout<<"read photo fail"<<endl;
		return -1;
	}
	namedWindow(WINDOW_NAME1,WINDOW_AUTOSIZE);
	imshow(WINDOW_NAME1,g_srcImage);
	namedWindow(WINDOW_NAME2);
	
	cvtColor(g_srcImage,g_grayImage,COLOR_BGR2GRAY);
	blur(g_grayImage,g_grayImage,Size(3,3));
	
	createTrackbar("阈值：",WINDOW_NAME2,&g_nThresh,g_nMaxThresh,on_ContoursChange);
	on_ContoursChange(0,0);
	waitKey(0);
	return 0;
}

void on_ContoursChange(int ,void *)
{
	Mat threshold_output;
	vector<vector<Point> >contours;
	vector<Vec4i>hierarchy;
	
	//检测边缘
	threshold(g_grayImage,threshold_output,g_nThresh,255,THRESH_BINARY);
	
	//找出轮廓
	findContours(threshold_output,contours,hierarchy,RETR_TREE,CHAIN_APPROX_SIMPLE,Point(0,0));
	
	//多边形逼近轮廓、获取矩形和圆形边界线
	vector<vector<Point> >contours_poly(contours.size());
	vector<Rect> boundRect(contours.size());
	vector<Point2f> center(contours.size());
	vector<float> radius(contours.size());
	
	for(unsigned int i=0;i<contours.size();i++)
	{
		//用制定精度逼近多边形曲线
		approxPolyDP(Mat(contours[i]),contours_poly[i],3,true);
		//计算点集最外面矩形边界
		boundRect[i] = boundingRect(Mat(contours_poly[i]));
		//对给定2D点集，寻找最小包围圆形
		minEnclosingCircle(contours_poly[i],center[i],radius[i]);
		
	}
	Mat drawing = Mat::zeros(threshold_output.size(),CV_8UC3);
	//绘制多边形轮廓、包围矩形框、圆形框
	for(unsigned int i=0;i<contours.size();i++)
	{
		Scalar color = Scalar(g_rng.uniform(0,255),g_rng.uniform(0,255),g_rng.uniform(0,255));
		drawContours(drawing,contours_poly,i,color,1,8,vector<Vec4i>(),0,Point());
		rectangle(drawing,boundRect[i].tl(),boundRect[i].br(),color,2,8,0);
		circle(drawing,center[i],(int)radius[i],color,2,8,0);
	}
	imshow(WINDOW_NAME2,drawing);
}

--------------来自opencv3编程入门毛星云pdf

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