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approxPolyDP 轮廓周围绘制矩形

approxPolyDP(InputArray  curve, OutputArray approxCurve,  double  epsilon,  bool  closed)curve：输入点集，二维点向量的集合approxCurve：输出点集，表示拟合曲线或多边形，数据与输入参数 curve 一致epsilon：指定的近似精度，原始曲线与近似曲线之间的最大距离close： 闭合标志，True 表示闭合多边形，False 表示多边形不闭合

boundingRect

boundingRect(InputArray points)得到轮廓周围最小矩形左上交点坐标和右下角点坐标，绘制一个矩形

minAreaRect

minAreaRect(InputArray  points)得到一个旋转的矩形，返回旋转矩形

绘制圆和椭圆

cv::minEnclosingCircle(InputArray points, //得到最小区域圆形Point2f& center, // 圆心位置float& radius)// 圆的半径
cv::fitEllipse(InputArray  points)得到最小椭圆

示例

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.h>using namespace std;
using namespace cv;
Mat src, gray_src, drawImg;
int threshold_v = 170;
int threshold_max = 255;
const char* output_win = "rectangle-demo";
RNG rng(12345);
void Contours_Callback(int, void*);
int main(int argc, char** argv) {src = imread("D:/vcprojects/images/hotball.png");if (!src.data) {printf("could not load image...\n");return -1;}cvtColor(src, gray_src, CV_BGR2GRAY);blur(gray_src, gray_src, Size(3, 3), Point(-1, -1));const char* source_win = "input image";namedWindow(source_win);namedWindow(output_win);imshow(source_win, src);createTrackbar("Threshold Value:", output_win, &threshold_v, threshold_max, Contours_Callback);Contours_Callback(0, 0);waitKey(0);return 0;
}void Contours_Callback(int, void*) {Mat binary_output;vector<vector<Point>> contours;vector<Vec4i> hierachy;threshold(gray_src, binary_output, threshold_v, threshold_max, THRESH_BINARY);//imshow("binary image", binary_output);findContours(binary_output, contours, hierachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(-1, -1));vector<vector<Point>> contours_ploy(contours.size());vector<Rect> ploy_rects(contours.size());vector<Point2f> ccs(contours.size());vector<float> radius(contours.size());vector<RotatedRect> minRects(contours.size());vector<RotatedRect> myellipse(contours.size());for (size_t i = 0; i < contours.size(); i++) {approxPolyDP(Mat(contours[i]), contours_ploy[i], 3, true);ploy_rects[i] = boundingRect(contours_ploy[i]);minEnclosingCircle(contours_ploy[i], ccs[i], radius[i]);if (contours_ploy[i].size() > 5) {myellipse[i] = fitEllipse(contours_ploy[i]);minRects[i] = minAreaRect(contours_ploy[i]);}}// draw itdrawImg = Mat::zeros(src.size(), src.type());Point2f pts[4];for (size_t t = 0; t < contours.size(); t++) {Scalar color = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255));//rectangle(drawImg, ploy_rects[t], color, 2, 8);//circle(drawImg, ccs[t], radius[t], color, 2, 8);if (contours_ploy[t].size() > 5) {ellipse(drawImg, myellipse[t], color, 1, 8);minRects[t].points(pts);for (int r = 0; r < 4; r++) {line(drawImg, pts[r], pts[(r + 1) % 4], color, 1, 8);}}}imshow(output_win, drawImg);return;
}