How to find angle betwene to lines

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i have two lines that will be draw through mouse events and to find the angle between them like if i draw two parallel line the angle give me 0

What I have tried:

Python

import numpy as np
import cv2
import math

btn_down = False

def get_points(im):
    # Set up data to send to mouse handler
    data = {}
    data['im'] = im.copy()
    data['lines'] = []

    # Set the callback function for any mouse event
    cv2.imshow("Image", im)
    cv2.setMouseCallback("Image", mouse_handler,data)
    cv2.waitKey(0)

    # Convert array to np.array in shape n,2,2
    points = np.uint16(data['lines'])

    return points, data['im']

def mouse_handler(event, x, y, flags, data):
    global btn_down

    if event == cv2.EVENT_LBUTTONUP and btn_down:
        #if you release the button, finish the line
        btn_down = False
        data['lines'][0].append((x, y)) #append the seconf point
        cv2.circle(data['im'], (x, y), 3, (0, 0, 255),5)
        cv2.line(data['im'], data['lines'][0][0], data['lines'][0][1], (0,0,255), 2)
        cv2.imshow("Image", data['im'])

    elif event == cv2.EVENT_MOUSEMOVE and btn_down:
        #thi is just for a ine visualization
        image = data['im'].copy()
        cv2.line(image, data['lines'][0][0], (x, y), (0,0,0), 1)
        cv2.imshow("Image", image)

    elif event == cv2.EVENT_LBUTTONDOWN:
        btn_down = True
        data['lines'].insert(0,[(x, y)]) #prepend the point
        cv2.circle(data['im'], (x, y), 3, (0, 0, 255), 5, 16)
        cv2.imshow("Image", data['im'])

def gradient(pt1, pt2):
    return (pt2[1] - pt1[1]) / (pt2[0] - pt1[0])

def getangle(pt1,pt2,pt3,pt4):
    pt1,pt2,pt3,pt4 =    data['im'][-4:]
    #last_points = pts[-4:]
    #pt2 = pts[-1][0]
    #pt1 = pts[-2][0]
    #pt3 = pts[-2][1]
    print(f"point1: {pt1} \n point2: {pt2} \n point3 : {pt3}")
    m1 = gradient(pt1, pt2)
    m2 = gradient(pt1, pt3)
    angR = math.atan((m2 - m1) / (1 + (m2 * m1)))
    angD = math.degrees(angR)
    cv2.putText(final_image, str(angD), (pt1[0] - 20, pt1[1] - 20), cv2.FONT_HERSHEY_COMPLEX,1, (0, 0, 255), 2)
    print(f"angle: {angD} \n angleR: {angR}")


# Running the code
img = cv2.imread('2.jpg', 1)
pts, final_image = get_points(img)

while True:
    if len(pts) % 4 == 0 and len(pts) != 0:
        getangle( data['im'])
        cv2.imshow('Image', final_image)
        print(pts[-2:])
        # pts1 = pts[-1]
        # print(f"point 1 : {pts1[0]}")
        cv2.waitKey(0)

Posted 16-Dec-20 20:04pm

Member 14649324

Updated 16-Dec-20 21:46pm

Richard Deeming

v2

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Sandeep Mewara · Answer 1 · 2020-12-16T20:54:00

You can make use of use the Hough Transform as mentioned here: How to measure the angle between 2 lines in a same image using python opencv? - Stack Overflow[^]

Snippet from there:

Python

from skimage.transform import (hough_line, hough_line_peaks)
import numpy as np
import cv2

image = cv2.imread('2.png')

# Compute arithmetic mean
image = np.mean(image, axis=2)

# Perform Hough Transformation to detect lines
hspace, angles, distances = hough_line(image)

# Find angle
angle=[]
for _, a , distances in zip(*hough_line_peaks(hspace, angles, distances)):
    angle.append(a)

# Obtain angle for each line
angles = [a*180/np.pi for a in angle]

# Compute difference between the two lines
angle_difference = np.max(angles) - np.min(angles)
print(angle_difference)