minarearect 源码_minAreaRect函数

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++:RotatedRectminAreaRect(InputArraypoints)

InputArraypoints：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 rectangle

C++:

Rect

RotatedRect::

boundingRect

(

)

const

C++:

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

#include

#include

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 > contours;

vector 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 minRect( contours.size() );

vector 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(), 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

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 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;

}