Multiple Horizontal & Vertical Lines are not showing

Question

Here i am trying to find the height of the water using opencv, hough transform. This program consist of canny edge detection, background subtraction, then the hough transform and height estimation. Then using the height it plot the graph.But this only detects the vertical lines. Multiple Horizontal & vertical lines are not showing. Any problem with the code?

Output of the program:

from imutils.perspective import four_point_transform
from imutils import paths
import numpy as np
import imutils 
import argparse
import cv2
import random
import math
import matplotlib.pyplot as plt

scaling_factorx = 0.8
scaling_factory = 0.8

cap = cv2.VideoCapture(0)
fgbg = cv2.createBackgroundSubtractorMOG2()
cap.set(3,640)
cap.set(4,480)
count = 0
height = []

while(1):

    ret, frame = cap.read()

    if frame is None:
        break
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    edges = cv2.Canny(gray, 1, 100)
    lines = cv2.HoughLinesP(edges, rho = 1,theta = 2*np.pi/180,threshold = 10,minLineLength = 100,maxLineGap = 10);
    if lines is not None:
        for line in lines[0]:
            dot1 = (line[0],line[1])
            dot2 = (line[2],line[3])
            cv2.line(frame, dot1, dot2, (255,0,0), 3)
            length = line[1] - line[3]
            print(length)
            height.append(length)

    cv2.imshow("output", frame)

    frame = cv2.resize(frame, None, fx = scaling_factorx, fy = scaling_factory, interpolation = cv2.INTER_AREA)

    fgmask = fgbg.apply(frame)
    cv2.imshow('frame', fgmask)

    gray_vid = cv2.cvtColor(frame, cv2.IMREAD_GRAYSCALE)
    cv2.imshow('Original', frame)

    edged_frame = cv2.Canny(frame, 1, 100)
    cv2.imshow('Edges', edged_frame)

    if cv2.waitKey(1) & 0xFF ==ord('q'):
        break

x = []
y = []

for i in range(len(height)):
    x.append(i)
    y.append(height[i])

cap.release()
cv2.destroyAllWindows()
print(x,y) 
plt.plot(x, y)  
plt.xlabel('x - axis') 
plt.ylabel('y - axis')  
plt.title('Height') 
plt.show()

Answer 1

You only draw one line because your for loop over lines is only looping over a single line.

if lines is not None:
    for line in lines: #for each line...not just one of them
        for x1,y1,x2,y2 in line:
            dot1 = (x1,y1)
            dot2 = (x2,y2)
            cv2.line(frame, dot1, dot2, (255,0,0), 3)
            length = y1 - y2
            print(length)
            height.append(length)