cv/geometry/line1.py

import cv2
import numpy as np

# define a video capture object
vid = cv2.VideoCapture(0)

while(True):

    # Capture the video frame
    # by frame
    ret, frame = vid.read()

    # Convert to grayscale.
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Apply edge detection method on the image
    edges = cv2.Canny(gray, 50, 150, apertureSize=3)

    # This returns an array of r and theta values
    lines = cv2.HoughLines(edges, 1, np.pi/180, 200)

    # The below for loop runs till r and theta values
    # are in the range of the 2d array

    if lines is not None:
        for r_theta in lines:
            arr = np.array(r_theta[0], dtype=np.float64)
            r, theta = arr
            # Stores the value of cos(theta) in a
            a = np.cos(theta)

            # Stores the value of sin(theta) in b
            b = np.sin(theta)

            # x0 stores the value rcos(theta)
            x0 = a*r

            # y0 stores the value rsin(theta)
            y0 = b*r

            # x1 stores the rounded off value of (rcos(theta)-1000sin(theta))
            x1 = int(x0 + 1000*(-b))

            # y1 stores the rounded off value of (rsin(theta)+1000cos(theta))
            y1 = int(y0 + 1000*(a))

            # x2 stores the rounded off value of (rcos(theta)+1000sin(theta))
            x2 = int(x0 - 1000*(-b))

            # y2 stores the rounded off value of (rsin(theta)-1000cos(theta))
            y2 = int(y0 - 1000*(a))

            # cv2.line draws a line in img from the point(x1,y1) to (x2,y2).
            # (0,0,255) denotes the colour of the line to be
            # drawn. In this case, it is red.
            cv2.line(frame, (x1, y1), (x2, y2), (0, 0, 255), 2)

    # Display the resulting frame
    cv2.imshow('frame', frame)

    # the 'q' button is set as the
    # quitting button you may use any
    # desired button of your choice
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# After the loop release the cap object
vid.release()
# Destroy all the windows
cv2.destroyAllWindows()