To find the angle, use this (simpler) code:
#include <opencv2/opencv.hpp>
using namespace cv;
#pragma comment(lib, "opencv_world331.lib")
#include <iostream>
#include <cmath>
using namespace std;
int main(void)
{
Mat frame = imread("rot.png");
cvtColor(frame, frame, CV_BGR2GRAY);
// Find the two circles.
vector<Vec3f> circles;
// Parameter values are very much obtained by trial and error
HoughCircles(frame, // input
circles, // output
CV_HOUGH_GRADIENT, // method
1, // dp
5, // minimum distance
5, // param1
24, // param2
0, // minimum radius
13); // maximum radius
if (circles.size() != 2)
{
cout << "Found " << circles.size() << " circles. You should find only two." << endl;
return 0;
}
Point2d centre1(circles[0][0], circles[0][1]);
Point2d centre2(circles[1][0], circles[1][1]);
circle(frame, centre1, 10, Scalar(0, 0, 0), 3);
circle(frame, centre2, 10, Scalar(0, 0, 0), 3);
// Calculate angle
double rise = circles[1][1] - circles[0][1];
double run = circles[1][0] - circles[0][0];
double slope = rise / run;
double angle_radians = atan(slope);
double angle_degrees = angle_radians*180.0 / CV_PI;
imshow("Hough Circles", frame);
waitKey(0);
return 0;
}
