How to detect lines using HoughLines in OpenCV (Java)?

Question

I\'m currently trying to detect whether a level crossing barrier has been deployed on an image using HoughLines in OpenCV. I thought my code would

Answer 1

Edit: See lordache's answer which is Java specific.

Useful reading: How are two-element vector represented in a OpenCV Mat in Java?

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Check this tutorial and look for the section "Standard Hough Line Transform".

lines should not be a cv::Mat, but a std::vector lines; that later on you can visualize with a code like the one showed in the link:

for( size_t i = 0; i < lines.size(); i++ )
{
  float rho = lines[i][0], theta = lines[i][1];
  Point pt1, pt2;
  double a = cos(theta), b = sin(theta);
  double x0 = a*rho, y0 = b*rho;
  pt1.x = cvRound(x0 + 1000*(-b));
  pt1.y = cvRound(y0 + 1000*(a));
  pt2.x = cvRound(x0 - 1000*(-b));
  pt2.y = cvRound(y0 - 1000*(a));
  line( cdst, pt1, pt2, Scalar(0,0,255), 3, CV_AA);
}