/examples/opencv/src/circle_detection.cpp

#include <cv.h>
#include <highgui.h>
#include <math.h>

int main(int argc, char** argv)
{
    IplImage* img = cvLoadImage("view_0002.png", 1);;
    IplImage* gray = cvCreateImage(cvGetSize(img), 8, 1);
    CvMemStorage* storage = cvCreateMemStorage(0);
    cvCvtColor(img, gray, CV_BGR2GRAY);
    cvSmooth(gray, gray, CV_GAUSSIAN, 9, 9); 
    CvSeq* circles = cvHoughCircles(gray, storage, 
        CV_HOUGH_GRADIENT, 2, 20, 10, 5, 5, 20);
    int i;

    for (i = 0; i < circles->total; i++) 
    {
         float* p = (float*)cvGetSeqElem( circles, i );
         cvCircle( img, cvPoint(cvRound(p[0]),cvRound(p[1])), 
             3, CV_RGB(0,255,0), -1, 8, 0 );
         cvCircle( img, cvPoint(cvRound(p[0]),cvRound(p[1])), 
             cvRound(p[2]), CV_RGB(255,0,0), 3, 8, 0 );
    }
    cvNamedWindow( "circles", 1 );
    cvShowImage( "circles", img );
    cvWaitKey(0);
    
    return 0;
}