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How Get Polar coordinate system Parameters:(R, theta) from HoughLines

asked 2014-05-15 10:16:20 -0500

abir gravatar image

updated 2014-05-16 02:17:54 -0500

berak gravatar image

Hi, I used the opencv documentation given by applying the algorithm of hough Libes on an image .

I have a problem, I can not get the value( R,theta) of the intersection between curves of every point in the image??

Please help me :) Thank you

this the code :http://docs.opencv.org/doc/tutorials/imgproc/imgtrans/hough_lines/hough_lines.html

#include "opencv2/imgproc/imgproc.hpp"

#include <iostream>

using namespace cv;
using namespace std;

void help()
{
 cout << "\nThis program demonstrates line finding with the Hough transform.\n"
         "Usage:\n"
         "./houghlines <image_name>, Default is pic1.jpg\n" << endl;
}

int main(int argc, char** argv)
{
 const char* filename = argc >= 2 ? argv[1] : "pic1.jpg";

 Mat src = imread(filename, 0);
 if(src.empty())
 {
     help();
     cout << "can not open " << filename << endl;
     return -1;
 }

 Mat dst, cdst;
 Canny(src, dst, 50, 200, 3);
 cvtColor(dst, cdst, CV_GRAY2BGR);

 #if 0
  vector<Vec2f> lines;
  HoughLines(dst, lines, 1, CV_PI/180, 100, 0, 0 );

  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);
  }
 #else
  vector<Vec4i> lines;
  HoughLinesP(dst, lines, 1, CV_PI/180, 50, 50, 10 );
  for( size_t i = 0; i < lines.size(); i++ )
  {
    Vec4i l = lines[i];
    line( cdst, Point(l[0], l[1]), Point(l[2], l[3]), Scalar(0,0,255), 3, CV_AA);
  }
 #endif
 imshow("source", src);
 imshow("detected lines", cdst);

 waitKey();

 return 0;
}
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Comments

Yes I know, I want to get all the array of values of rho and theta !!!

abir gravatar imageabir ( 2014-05-16 02:27:42 -0500 )edit

sorry abir, i misread it (in the deleted comment), and confused Houghlines and HoughlinesP

berak gravatar imageberak ( 2014-05-16 02:33:21 -0500 )edit

No problem , I want to get the orientation of the point d'intersection between lines !! For that I want to retrieve the values ​​of theta and rho!! please help me :)

abir gravatar imageabir ( 2014-05-16 02:38:30 -0500 )edit

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answered 2014-05-16 07:47:20 -0500

kbarni gravatar image

The theta (angle of line) is atan2(X1-X2,Y1-Y2).

The distance from origin rho is a point-line distance, the formula is here (#14): http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html

The X1,X2,Y1,Y2 are the members of the lines vector.

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Asked: 2014-05-15 10:16:20 -0500

Seen: 1,305 times

Last updated: May 16 '14