How can i get accurate center points?

Question

How can I get accurate center points with OpenCV Hough Circle Transformation? I need more decimal places of accurate in the x,y coordinates.

( on accurate i mean something like this) i got these center coordinates with matlab

x107,775526315904   y112,963480232638
x469,550463441518   y208,309866770404
x217,386414755458   y490,882895036058

Here is my code:

#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/core/core.hpp>
#include <iostream>
#include <stdio.h>

using namespace cv;
using namespace std;


int main()
{
    Mat src, src_gray, src0;
    printf("Give the name of the picture\n");
    char ImageName[20];
    scanf("%s", &ImageName);
    /// Read the image 
    src = imread(ImageName, 1);
    if (!src.data)
    {
        printf("no image data\n");
        return main();
    }
    // src0 = src;
    // imshow("orignal", src0);
    /// Convert it to gray
    cvtColor(src, src_gray, CV_BGR2GRAY);
    GaussianBlur(src_gray, src_gray, Size(9, 9), 2, 2);
    vector<Vec3f> circles;
    /// Apply the Hough Transform to find the circles
    HoughCircles(src_gray, circles, CV_HOUGH_GRADIENT, 0.92, src_gray.rows / 10, 20, 10, 55, 60);
    for (size_t i = 0; i < circles.size(); i++)
    {
        Point center(cvRound(circles[i][0]), cvRound(circles[i][1]));
        int radius = cvRound(circles[i][2]);
    //  printf("%d center x %d y %d\n", i, cvRound(circles[i][0]), cvRound(circles[i][1]));
    //  printf("rad: %d\n", cvRound(circles[i][2]));
        cout << i + 1 << " centerpoint " << " x: " << circles[i][0] << "   y: " << circles[i][1] << "rad: " << circles[i][2] << endl;
        // cout << i + 1 << " othermethod" << "x : " << center.x << endl;
        // circle center
        circle(src, center, 1, Scalar(0, 255, 0), -1, 8, 0);
        // circle outline
        circle(src, center, radius, Scalar(255, 0, 0), 1, 8, 0);
    }
    imshow("circlefinder", src);
    waitKey(1);
    system("PAUSE");
    cvDestroyWindow("orignal");
    cvDestroyWindow("circlefinder");
    printf("new picture ?(y/n)");
    char ans[1];
    scanf("%s", &ans);
    if (strcmp(ans, "y"))
    {
        return 0;
    }
    else if (strcmp(ans, "n"))
    {
        return main();
    }

}

Here is the output:

Give the name of the picture
as2.jpg
145.5test x
1 centerpoint  x: 105.5   y: 112.5rad: 55.5563
2 centerpoint  x: 235.5   y: 427.5rad: 56.626
3 centerpoint  x: 466.5   y: 196.5rad: 55.5203
A folytatáshoz nyomjon meg egy billentyűt . . .
new picture ?

Answer 1

It's not your data what is lost. It's just print function you made skipping some numbers.

Try std::setprecision:

std::cout << 432.123456789f << "   " << std::setprecision(10) << 432.123456789f << std::endl;

Don't forget:

#include <iomanip>

Anyway I don't think you really need that precission. Your measure error in image processing is usually quite big and last digits don't give you any real information.