std::pow Problem

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Hi

In this code I'm trying to detect eye pupil but there is an error I would be grateful if you help me

Error : 1>source.cpp(36): error C2668: 'std::pow' : ambiguous call to overloaded function

#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include<cmath>;

int main(int argc, char** argv)
{
// Load image
cv::Mat src = cv::imread("1.jpg");
if (src.empty())
    return -1;

// Invert the source image and convert to grayscale
cv::Mat gray;
cv::cvtColor(~src, gray, CV_BGR2GRAY);

// Convert to binary image by thresholding it
cv::threshold(gray, gray, 220, 255, cv::THRESH_BINARY);

// Find all contours
std::vector<std::vector<cv::Point> > contours;
cv::findContours(gray.clone(), contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);

// Fill holes in each contour
cv::drawContours(gray, contours, -1, CV_RGB(255,255,255), -1);

for (int i = 0; i < contours.size(); i++)
{
    double area = cv::contourArea(contours[i]);
    cv::Rect rect = cv::boundingRect(contours[i]);
    int radius = rect.width/2;

    // If contour is big enough and has round shape
    // Then it is the pupil
    if (area >= 30 && 
        std::abs(1 - ((double)rect.width / (double)rect.height)) <= 0.2 &&
            std::abs(1 - (area / (CV_PI * std::pow(radius, 2)))) <= 0.2)    
    {
        cv::circle(src, cv::Point(rect.x + radius, rect.y + radius), radius, CV_RGB(255,0,0), 2);
    }
}

cv::imshow("image", src);
cv::waitKey(0);

return 0;

}