# 【OpenCV】- 多边形将轮廓包围

##### 1、返回外部矩形边界：boundingRect()函数

Rect point=boundingRect(InputArray points)


##### 2、寻找最小包围矩形：minAreaRect()函数

RotatedRect box=minAreaRect(InputArray points)


#include<opencv2/opencv.hpp>
#include<opencv2/imgproc/imgproc.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<iostream>
using namespace std;
using namespace cv;
int main()
{
Mat image(600, 600, CV_8UC3);
RNG& rng = theRNG();
while (1)
{
//参数初始化
int count = rng.uniform(3, 103);
vector<Point> points;
for (int i = 0; i < count; i++)
{
Point point;
point.x = rng.uniform(image.cols / 4, image.cols * 3 / 4);
point.y = rng.uniform(image.rows / 4, image.rows * 3 / 4);
points.push_back(point);
}
//给定的2D点集，寻找最小面积的包围矩形
RotatedRect box = minAreaRect(Mat(points));
//
Point2f vertex[4];
box.points(vertex);
//绘制出随机颜色的点
image = Scalar::all(0);
for (int i = 0; i < count; i++)
{
circle(image, points[i], 3, Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255)), FILLED,LINE_AA);
}
//绘制出最小面积的包围矩形
for (int i = 0; i < 4; i++)
{
//第一个线段的终点，又是第二个线段的起点
line(image, vertex[i], vertex[(i + 1) % 4], Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255)), 2, LINE_AA);
cout << vertex[i] << ":" << vertex[(i + 1) % 4] << endl;
}
imshow("矩形包围示例", image);
char key = (char)waitKey();
if (key == 27 || key == 'q' || key == 'Q')
break;

}
return 0;
}


##### 3、寻找最小包围圆形：minEnclosingCircle()函数

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

• 第一个参数：输入的二维点集，可以为std::vector<>或Mat类型
• 第二个参数：圆的输出圆心
• 第三个参数：圆的输出半径

#include<opencv2/opencv.hpp>
#include<opencv2/imgproc/imgproc.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<iostream>
using namespace std;
using namespace cv;
int main()
{
Mat image(600, 600, CV_8UC3);
RNG& rng = theRNG();
while (1)
{
//参数初始化
int count = rng.uniform(3, 103);
vector<Point> points;
for (int i = 0; i < count; i++)
{
Point point;
point.x = rng.uniform(image.cols / 4, image.cols * 3 / 4);
point.y = rng.uniform(image.rows / 4, image.rows * 3 / 4);
points.push_back(point);
}
//给定的2D点集，寻找最小面积的包围圆
Point2f center;
//绘制出随机颜色的点
image = Scalar::all(0);
for (int i = 0; i < count; i++)
{
circle(image, points[i], 3, Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255)), FILLED,LINE_AA);
}
//绘制出最小面积的包围矩形
circle(image, center, radius, Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255)), 2, LINE_AA);
cout << center << ":" << radius << endl;
imshow("圆形包围示例", image);
char key = (char)waitKey();
if (key == 27 || key == 'q' || key == 'Q')
break;

}
return 0;
}


##### 4、用椭圆拟合二维点集：fitEllipse()函数

void RotatedRect fitEllipse(InputArray points)

##### 5、逼近多边形曲线：approxPolyDP()函数

void approxPolyDP(InputArray curve,OutputArray approxCurve,double epsilon,bool closed)


##### 6、综合示例程序：使用多边形包围轮廓
#include<opencv2/opencv.hpp>
#include<opencv2/imgproc/imgproc.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<iostream>
using namespace std;
using namespace cv;
#define WINDOW_NAME1 "【原始图窗口】"
#define WINDOW_NAME2 "【效果图窗口】"
Mat g_srcImage; Mat g_grayImage;
int g_nThresh = 50; //阈值
int g_maxThresh = 255;  //阈值最大值
RNG g_rng(12345); //随机数生成器
static void ShowHelpTxte();
void on_ContoursChange(int, void *);
int main()
{
system("color 1A");
//加载源图像
//得到的原图转换为灰度并进行平滑
cvtColor(g_srcImage, g_grayImage, COLOR_BGR2GRAY);
blur(g_grayImage, g_grayImage, Size(3, 3));
namedWindow(WINDOW_NAME1, WINDOW_AUTOSIZE);
imshow(WINDOW_NAME1, g_srcImage);

createTrackbar("阈值：", WINDOW_NAME1, &g_nThresh, g_maxThresh, on_ContoursChange);
on_ContoursChange(0, 0);//调用一次进行初始化
waitKey(0);
return 0;
}
void on_ContoursChange(int, void *)
{
//定义一些参数
Mat threshold_output;
vector<vector<Point>> contours;
vector<Vec4i>hierarchy;
//对图像进行二值化，控制阈值
threshold(g_grayImage, threshold_output, g_nThresh, 255, THRESH_BINARY);
//寻找轮廓;
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框
vector<vector<Point>>contours_poly(contours.size());
vector<Rect> boundRect(contours.size());
vector<Point2f>center(contours.size());
//一个循环，遍历所有部分
for (unsigned int i = 0; i < contours.size(); i++)
{
//用指定精度逼近多边形曲线
approxPolyDP(Mat(contours[i]), contours_poly[i], 3, true);
//计算点集的最外面（up-right)矩形边界
boundRect[i] = boundingRect(Mat(contours_poly[i]));
//对给定的2D点集，寻找最小面积的包围圆形
}
//绘制多边形轮廓+包围矩形框+圆形框
Mat drawing = Mat::zeros(threshold_output.size(), CV_8UC3);
for (int unsigned i = 0; i < contours.size(); i++)
{
Scalar color = Scalar(g_rng.uniform(0, 255), g_rng.uniform(0, 255), g_rng.uniform(0, 255));
//绘制轮廓
drawContours(drawing, contours_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point());
//绘制矩形
rectangle(drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0);
//绘制圆形
circle(drawing, center[i], (int)radius[i], color, 2, 8, 0);
}
namedWindow(WINDOW_NAME2, WINDOW_AUTOSIZE);
imshow(WINDOW_NAME2, drawing);

}


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