Linetracking with opencv

Overview

This Tutorial will show how to make a line detection and find a center of line for a line following pi car.

Materials/Prerequisites

You will need a Raspberry pi 3 with python installed and Pi camera (Webcam works too). you also need to install OpenCV onto your Raspberry Pi. We can follow instructions to install OpenCV. If it is the first time to use pi camera, to be able to access the Raspberry pi camera with OpenCV and Python, we recommend to look at this instruction. For interfacing with the Raspberry Pi camera module using Python, the basic idea is to install picamera module with NumPy array support since OpenCV represents images as NumPy arrays when using Python bindings.

Process

If you are using Webcam, you can follow this link to realize line detection. The code is given below:

import sys
import time
import cv2
import numpy as np
import os

Kernel_size=15
low_threshold=40
high_threshold=120

rho=10
threshold=15
theta=np.pi/180
minLineLength=10
maxLineGap=1

Initialize camera
video_capture = cv2.VideoCapture(0)

while True:
    # CAPTURE FRAME-BY-FRAME
    ret, frame = video_capture.read()
    time.sleep(0.1)
    #Convert to Grayscale
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    #Blur image to reduce noise. if Kernel_size is bigger the image will be more blurry
    blurred = cv2.GaussianBlur(gray, (Kernel_size, Kernel_size), 0)
    
    #Perform canny edge-detection.
    #If a pixel gradient is higher than high_threshold is considered as an edge.
    #if a pixel gradient is lower than low_threshold is is rejected , it is not an edge.
    #Bigger high_threshold values will provoque to find less edges.
    #Canny recommended ratio upper:lower  between 2:1 or 3:1
    edged = cv2.Canny(blurred, low_threshold, high_threshold)
    #Perform hough lines probalistic transform
    lines = cv2.HoughLinesP(edged,rho,theta,threshold,minLineLength,maxLineGap)
    
    #Draw cicrcles in the center of the picture
    cv2.circle(frame,(320,240),20,(0,0,255),1)
    cv2.circle(frame,(320,240),10,(0,255,0),1)
    cv2.circle(frame,(320,240),2,(255,0,0),2)
    
    #With this for loops only a dots matrix is painted on the picture
    #for y in range(0,480,20):
            #for x in range(0,640,20):
                #cv2.line(frame,(x,y),(x,y),(0,255,255),2)
    
    #With this for loops a grid is painted on the picture
    for y in range(0,480,40):
            cv2.line(frame,(0,y),(640,y),(255,0,0),1)
            for x in range(0,640,40):
                cv2.line(frame,(x,0),(x,480),(255,0,0),1)
                
    #Draw lines on input image
    if(lines != None):
        for x1,y1,x2,y2 in lines[0]:
            cv2.line(frame,(x1,y1),(x2,y2),(0,255,0),2)
            cv2.putText(frame,'lines_detected',(50,50),cv2.FONT_HERSHEY_SIMPLEX,1,(0,255,0),1)
    cv2.imshow("line detect test", frame)

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

# When everything is done, release the capture

video_capture.release()
cv2.destroyAllWindows()

Authors

Pi Car Discovery Group

Group Link

group project page

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