Android OpenCV Drawing Hough Lines

Question

I am trying to use OpenCV on an android phone to detect lines. I modified the \'Tutorial 1 Basic - 2. Use OpenCV Camera\' sample. I am also using Hough Line Transform as an

Answer 1

Here is my code for visual studio, hope it helps.

void drawLines(Mat &input, const std::vector &lines) {
for (int i = 0; i < lines.size(); i++) {
    float alpha = CV_PI/2-atan(input.rows/input.cols);
    float r_max;
    float r_min;
    float r = lines[i][0];
    float theta = lines[i][1];
    if (thetaCV_PI-alpha) {
        r_max = input.cols*cos(theta);
        r_min = input.rows*sin(theta);
        if (r > r_max) {
            Point pt1(input.cols, (r - input.cols*cos(theta)) / sin(theta));
            Point pt2((r - input.rows*sin(theta)) / cos(theta), input.rows);
            line(input, pt1, pt2, Scalar(255, 0, 0), 1);
        }
        else if (r < r_max && r > r_min) {
            Point pt1(r / cos(theta), 0);
            Point pt2((r - input.rows*sin(theta)) / cos(theta), input.rows);
            line(input, pt1, pt2, Scalar(255, 0, 0), 1);
        }
        else {
            Point pt1(r / cos(theta), 0);
            Point pt2(0, r / sin(theta));
            line(input, pt1, pt2, Scalar(255, 0, 0), 1);
        }

    }
    else {
            r_min = input.cols*cos(theta);
            r_max = input.rows*sin(theta);
            if (r > r_max) {
                Point pt1(input.cols, (r - input.cols*cos(theta)) / sin(theta));
                Point pt2((r - input.rows*sin(theta)) / cos(theta), input.rows);
                line(input, pt1, pt2, Scalar(0, 0, 255), 1);
            }
            else if (r < r_max && r > r_min) {
                Point pt1(input.cols, (r - input.cols*cos(theta)) / sin(theta));
                Point pt2(0, r / sin(theta));
                line(input, pt1, pt2, Scalar(0, 0, 255), 1);
            }
            else {
                Point pt1(r / cos(theta), 0);
                Point pt2(0, r / sin(theta));
                line(input, pt1, pt2, Scalar(0, 0, 255), 1);
            }
    }

}

Here are 2 graphs about the logic about my code I posted.

The explanation of alpha

The explanation of r_max && r_min