Detecting Road from satellite image in OpenCV - c++

Question

I'm trying to detect roads from a satellite image! It can be any type of paved/asphalt road. I'm using OpenCV! The way I am trying is, first I used Canny to detect the edges, the I am trying to apply hough transform to detect the straight lines from the edges. Then I planned to detect circles to detect the curves of the roads. The problem I'm facing is, after doing canny, hough is not working. Here is my code so far:
#include <iostream>
#include <math.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace cv;
using namespace std;
int main()
{
//read an image
cv::Mat image = cv::imread("img2.jpg");
//create image window named "My Image"
cv::namedWindow("My Image");
//show the image on the window
cv::imshow("My Image", image);
cv::Mat contours,hough;
//canny
cv::Canny(image, contours, 0, 100);
cv::namedWindow("My Image2");
cv::imshow("My Image2", contours);
// Hough tranform for line detection
std::vector<cv::Vec2f> lines;
cv::HoughLines(contours, lines, 1, CV_PI/180, 80, 0, 0);
std::vector<cv::Vec2f>::const_iterator it= lines.begin();
while(it!=lines.end())
{
float rho= (*it)[0];
// first element is distance rho
float theta= (*it)[1];
//second element is angle theta
if(theta < CV_PI/4. || theta > 3.*CV_PI/4.)
{ // ~vertical line
// point of intersection of the line with first row
cv::Point pt1(rho/cos(theta),0);
// point of intersection of the line with last row
cv::Point pt2((rho-result.rows*sin(theta))/cos(theta),result.rows);
// draw a white line
cv::line( image, pt1, pt2, cv::Scalar(255), 1);
}
else
{ // ~horizontal line
// point of intersection of the
// line with first column
cv::Point pt1(0,rho/sin(theta));
// point of intersection of the line with last column
cv::Point pt2(result.cols,(rho-result.cols*cos(theta))/sin(theta));
// draw a white line
cv::line(image, pt1, pt2, cv::Scalar(255), 1);
}
++it;
}
//show lines
cv::namedWindow("My Image3");
cv::imshow("My Image3", hough);
//wait key for 5000ms
cv::waitKey(80000);
return 0;
}
In this code, I'm getting an error under "result" at line cv::Point pt2((rho-result.rows*sin(theta))/cos(theta),result.rows);
And another error under "result" at line cv::Point pt2(result.cols,(rho-result.cols*cos(theta))/sin(theta));
I can't figure it out what errors are those and what are the solutions! Any help would be appreciated :)
Also I'm totally new at computer vision, if you have any other easier and simpler way to accomplish my goal please feel free to share it :)
For your help I'm giving the sample image and the image of errors:
https://drive.google.com/open?id=0B4qYRvG5emZDWXhNV2V2djZWdUk
Error is for the errors, Canny is after performing canny algorithm and input is the sample image I took!
NOTE: I'm following OpenCV cookbook for my codes!