原文链接地址：
http://blog.csdn.net/qq_18343569/article/details/48000179
1、minAreaRect函数
函数作用：
主要求得包含点集最小面积的矩形，，这个矩形是可以有偏转角度的，可以与图像的边界不平行
2、minAreaRect函数调用形式
C++: RotatedRect minAreaRect(InputArray points)
InputArray points：表示输入的点集
输出是矩形的四个点坐标
RotatedRect
class RotatedRect
class CV_EXPORTS RotatedRect
{
public:
//! various constructors
RotatedRect();
RotatedRect(const Point2f& center, const Size2f& size, float angle);
RotatedRect(const CvBox2D& box);
//! returns 4 vertices of the rectangle
void points(Point2f pts[]) const;
//! returns the minimal up-right rectangle containing the rotated rectangle
Rect boundingRect() const;
//! conversion to the old-style CvBox2D structure
operator CvBox2D() const;
Point2f center; //< the rectangle mass center
Size2f size; //< width and height of the rectangle
float angle; //< the rotation angle. When the angle is 0, 90, 180, 270 etc., the rectangle becomes an up-right rectangle.
};
The class represents rotated (i.e. not up-right) rectangles on a plane. Each rectangle is specified by the center point (mass center), length of each side (represented by cv::Size2f structure) and the rotation angle in degrees.
C++: RotatedRect::RotatedRect()C++: RotatedRect::RotatedRect(const Point2f& center, const Size2f& size, float angle)C++: RotatedRect::RotatedRect(const CvBox2D& box)
Parameters:
•center – The rectangle mass center.
•size – Width and height of the rectangle.
•angle – The rotation angle in a clockwise direction. When the angle is 0, 90, 180, 270 etc., the rectangle becomes an up-right rectangle.
•box – The rotated rectangle parameters as the obsolete CvBox2D structure.
C++: void RotatedRect::points(Point2f pts[]) const //! returns 4 vertices of the rectangleC++: Rect RotatedRect::boundingRect() constC++: RotatedRect::operator CvBox2D() const
Parameters:
•pts – The points array for storing rectangle vertices.
The sample below demonstrates how to use RotatedRect:
Mat image(200, 200, CV_8UC3, Scalar(0));
RotatedRect rRect = RotatedRect(Point2f(100,100), Size2f(100,50), 30);
Point2f vertices[4];
rRect.points(vertices);//获取矩形的四个点
for (int i = 0; i < 4; i++)
line(image, vertices[i], vertices[(i+1)%4], Scalar(0,255,0));
Rect brect = rRect.boundingRect();
rectangle(image, brect, Scalar(255,0,0));
imshow("rectangles", image);
waitKey(0);
3、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);
/// Function header
void thresh_callback(int, void* );
/** @function main */
int main( int argc, char** argv )
{
/// 加载源图像
src = imread( argv[1], 1 );
/// 转为灰度图并模糊化
cvtColor( src, src_gray, CV_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );
/// 创建窗体
char* source_window = "Source";
namedWindow( source_window, CV_WINDOW_AUTOSIZE );
imshow( source_window, src );
createTrackbar( " Threshold:", "Source", &thresh, max_thresh, thresh_callback );
thresh_callback( 0, 0 );
waitKey(0);
return(0);
}
/** @function thresh_callback */
void thresh_callback(int, void* )
{
Mat threshold_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
/// 阈值化检测边界
threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
/// 寻找轮廓
findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
/// 对每个找到的轮廓创建可倾斜的边界框和椭圆
vector<RotatedRect> minRect( contours.size() );
vector<RotatedRect> minEllipse( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{ minRect[i] = minAreaRect( Mat(contours[i]) );
if( contours[i].size() > 5 )
{ minEllipse[i] = fitEllipse( Mat(contours[i]) ); }
}
/// 绘出轮廓及其可倾斜的边界框和边界椭圆
Mat drawing = Mat::zeros( threshold_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) );
// contour
drawContours( drawing, contours, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
// ellipse
ellipse( drawing, minEllipse[i], color, 2, 8 );
// rotated rectangle
Point2f rect_points[4]; minRect[i].points( rect_points );
for( int j = 0; j < 4; j++ )
line( drawing, rect_points[j], rect_points[(j+1)%4], color, 1, 8 );
}
/// 结果在窗体中显示
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
}
opencv源码：
#include "stdafx.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
using namespace cv;
using namespace std;
void help()
{
cout << "This program demonstrates finding the minimum enclosing box or circle of a set\n"
"of points using functions: minAreaRect() minEnclosingCircle().\n"
"Random points are generated and then enclosed.\n"
"Call:\n"
"./minarea\n"
"Using OpenCV version %s\n" << CV_VERSION << "\n" << endl;
}
int main( int /*argc*/, char** /*argv*/ )
{
help();
Mat img(500, 500, CV_8UC3);
RNG& rng = theRNG();
for(;;)
{
int i, count = rng.uniform(1, 101);
vector<Point> points;
for( i = 0; i < count; i++ )
{
Point pt;
pt.x = rng.uniform(img.cols/4, img.cols*3/4);
pt.y = rng.uniform(img.rows/4, img.rows*3/4);
points.push_back(pt);
}
RotatedRect box = minAreaRect(Mat(points));
Point2f center, vtx[4];
float radius = 0;
minEnclosingCircle(Mat(points), center, radius);
box.points(vtx);
img = Scalar::all(0);
for( i = 0; i < count; i++ )
circle( img, points[i], 3, Scalar(0, 0, 255), CV_FILLED, CV_AA );
for( i = 0; i < 4; i++ )
line(img, vtx[i], vtx[(i+1)%4], Scalar(0, 255, 0), 1, CV_AA);
circle(img, center, cvRound(radius), Scalar(0, 255, 255), 1, CV_AA);
imshow( "rect & circle", img );
char key = (char)cvWaitKey();
if( key == 27 || key == 'q' || key == 'Q' ) // 'ESC'
break;
}
return 0;
}
