title: How to measure the angle between 2 lines in a same image using python opencv?
body: <p>I have detected a lane boundary line which is not straight using hough transform and then extracted that line separately. Then blended with another image that has a straight line. Now I need to calculate the angle between those two lines, but I do not know the coordinates of those lines. So I tried with code that gives the coordinates of vertical lines, but it can not specifically identify those coordinates. Is there a way to measure the angle between those lines? Here is my coordinate calculation code and blended image with two lines </p>
  
  <pre><code>import cv2 as cv
  import numpy as np
  
  src = cv.imread("blended2.png", cv.IMREAD_COLOR)
  
  if len(src.shape) != 2:
      gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
  else:
      gray = src
  
  gray = cv.bitwise_not(gray)
  bw = cv.adaptiveThreshold(gray, 255, cv.ADAPTIVE_THRESH_MEAN_C, cv.THRESH_BINARY, 15, -2)
  
  horizontal = np.copy(bw)
  vertical = np.copy(bw)
  
  cols = horizontal.shape[1]
  horizontal_size = int(cols / 30)
  
  horizontalStructure = cv.getStructuringElement(cv.MORPH_RECT, (horizontal_size, 1))
  horizontal = cv.erode(horizontal, horizontalStructure)
  horizontal = cv.dilate(horizontal, horizontalStructure)
  
  cv.imwrite("img_horizontal8.png", horizontal)
  
  h_transpose = np.transpose(np.nonzero(horizontal))
  print("h_transpose")
  print(h_transpose[:100])
  
  rows = vertical.shape[0]
  verticalsize = int(rows / 30)
  verticalStructure = cv.getStructuringElement(cv.MORPH_RECT, (1, verticalsize))
  vertical = cv.erode(vertical, verticalStructure)
  vertical = cv.dilate(vertical, verticalStructure)
  
  cv.imwrite("img_vertical8.png", vertical)
  
  v_transpose = np.transpose(np.nonzero(vertical))
  
  print("v_transpose")
  print(v_transpose[:100])
  
  img = src.copy()
  
  # edges = cv.Canny(vertical,50,150,apertureSize = 3)
  minLineLength = 100
  maxLineGap = 200
  lines = cv.HoughLinesP(vertical,1,np.pi/180,100,minLineLength,maxLineGap)
  for line in lines:
      for x1,y1,x2,y2 in line:
          cv.line(img,(x1,y1),(x2,y2),(0,255,0),2)
  
  cv.imshow('houghlinesP_vert', img)
  cv.waitKey(0)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/Fsumj.png" alt="enter image here"></p>