Jetson 21 Line Following Autonomous Driving with OpenCV
From Waveshare Wiki
In this tutorial, we'll use the basic functionalities of OpenCV to detect yellow lines (default color) in the image and control the direction of the chassis based on the position of these lines. Please note that in this example, the chassis won't move. Instead, we'll only showcase the algorithms using OpenCV on the image. For safety reasons, we won't integrate motion control in this tutorial, as it's heavily influenced by external factors. Users should fully understand the code's functionality before adding corresponding motion control features.
If you want to control the robot's movement through this example, please refer to the "Python Chassis Motion Control" section to add the relevant motion control functions (our open-source example is located in robot_ctrl.py).
Preparation
Since the product automatically runs the main program at startup, which occupies the camera resource, this tutorial cannot be used in such situations. You need to terminate the main program or disable its automatic startup before restarting the robot.
It's worth noting that because the robot's main program uses multi-threading and is configured to run automatically at startup through crontab, the usual method sudo killall python typically doesn't work. Therefore, we'll introduce the method of disabling the automatic startup of the main program here.
If you have already disabled the automatic startup of the robot's main demo, you do not need to proceed with the section on Terminate the Main Demo.
Terminate the Main Demo
- 1. Click the "+" icon next to the tab for this page to open a new tab called "Launcher."
- 2. Click on "Terminal" under "Other" to open a terminal window.
- 3. Type bash into the terminal window and press Enter.
- 4. Now you can use the Bash Shell to control the robot.
- 5. Enter the command: sudo killall -9 python.
Example
The following code block can be run directly:
- 1. Select the code block below.
- 2. Press Shift + Enter to run the code block.
- 3. Watch the real-time video window.
- 4. Press STOP to close the real-time video and release the camera resources.
If you cannot see the real-time camera feed when running:
- Click on Kernel -> Shut down all kernels above.
- Close the current section tab and open it again.
- Click STOP to release the camera resources, then run the code block again.
- Reboot the device.
Note
If you use the USB camera you need to uncomment frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB).
Features of this Section
After running the following code block, you can place a yellow tape in front of the camera and observe if there are contours of the yellow tape in the black screen. Try to detect the yellow tape using two target detection lines.
import cv2 # Import OpenCV library for image process
import imutils, math # Library to aid image processing and mathematical operations
from picamera2 import Picamera2 # For accessing the library of Raspberry Pi Camera
import numpy as np
from IPython.display import display, Image # Display images on Jupyter Notebook
import ipywidgets as widgets # Widgets for creating interactive interfaces, such as buttons
import threading # Used to create new threads for asynchronous execution of tasks
# Stop button
# ================
stopButton = widgets.ToggleButton(
value=False,
description='Stop',
disabled=False,
button_style='danger', # 'success', 'info', 'warning', 'danger' or ''
tooltip='Description',
icon='square' # (FontAwesome names without the `fa-` prefix)
)
# findline autodrive
# Upper sampling line, 0.6 for position, higher values
sampling_line_1 = 0.6
# Lower sampling line, the value needs to be greater than sampling_line_1 and less than 1
sampling_line_2 = 0.9
# Detect line slope effect on turning
slope_impact = 1.5
# The effect of line position detected by the lower detection line on turning
base_impact = 0.005
# The effect of the current speed on turning
speed_impact = 0.5
# Tracking line speed
line_track_speed = 0.3
# The effect of slop on speed
slope_on_speed = 0.1
# Color of target line, HSV color space
line_lower = np.array([25, 150, 70])
line_upper = np.array([42, 255, 255])
def view(button):
# If you are using a CSI camera you need to comment out the picam2 code and the camera code
# Since the latest versions of OpenCV no longer support CSI cameras (4.9.0.80), you need to use picamera2 to get the camera footage
# picam2 = Picamera2() # Create Picamera2 example
# Configure camera parameters and set the format and size of video
# picam2.configure(picam2.create_video_configuration(main={"format": 'XRGB8888', "size": (640, 480)}))
# picam2.start() # Start camera
camera = cv2.VideoCapture(-1) # Create camera example
#Set resolution
camera.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
camera.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)
display_handle=display(None, display_id=True)
while True:
# img = picam2.capture_array()
_, img = camera.read() # Capture a frame from camera
# frame = cv2.flip(frame, 1) # if your camera reverses your image
height, width = img.shape[:2]
center_x, center_y = width // 2, height // 2
# Image preprocessing includes color space conversion, Gaussian blur, and color range filtering, etc.
hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
line_mask = cv2.inRange(hsv, line_lower, line_upper) # Filter out target lines based on color ranges
line_mask = cv2.erode(line_mask, None, iterations=1) # Eroding operation to remove noise
line_mask = cv2.dilate(line_mask, None, iterations=1) # Expansion operation enhances the target line
# Detect the target line based on the positions of the upper and lower sampling lines, and calculate steering and velocity control signals according to the detection results
sampling_h1 = int(height * sampling_line_1)
sampling_h2 = int(height * sampling_line_2)
get_sampling_1 = line_mask[sampling_h1]
get_sampling_2 = line_mask[sampling_h2]
# Calculate the width of the target line at the upper and lower sampling lines
sampling_width_1 = np.sum(get_sampling_1 == 255)
sampling_width_2 = np.sum(get_sampling_2 == 255)
if sampling_width_1:
sam_1 = True
else:
sam_1 = False
if sampling_width_2:
sam_2 = True
else:
sam_2 = False
# Get the edge index of the target line at the upper and lower sampling lines
line_index_1 = np.where(get_sampling_1 == 255)
line_index_2 = np.where(get_sampling_2 == 255)
# If the target line is detected at the upper sampling line, calculate the center position of the target line
if sam_1:
sampling_1_left = line_index_1[0][0] # Index of the leftmost index of the upper sampling line target line
sampling_1_right = line_index_1[0][sampling_width_1 - 1] # Index to the far right of the upper sampling line target line
sampling_1_center= int((sampling_1_left + sampling_1_right) / 2) # Index of the center of the upper sampling line target line
# If a target line is detected at the lower sampling line, calculate the target line center position
if sam_2:
sampling_2_left = line_index_2[0][0]
sampling_2_right = line_index_2[0][sampling_width_2 - 1]
sampling_2_center= int((sampling_2_left + sampling_2_right) / 2)
# Initialize steering and speed control signals
line_slope = 0
input_speed = 0
input_turning = 0
# if the target line is detected at both sampling lines, calculate the slope of the line, and then calculate velocity and steering control signals based on the slope and the position of the target line.
if sam_1 and sam_2:
line_slope = (sampling_1_center - sampling_2_center) / abs(sampling_h1 - sampling_h2) # Calculate the slope of the line
impact_by_slope = slope_on_speed * abs(line_slope) #Calculate the effect on velocity based on the slope
input_speed = line_track_speed - impact_by_slope #Calculate speed control signal
input_turning = -(line_slope * slope_impact + (sampling_2_center - center_x) * base_impact) #+ (speed_impact * input_speed) # Calculating steering control signals
elif not sam_1 and sam_2: # If the target line is detected only at the lower sampling line
input_speed = 0 # Set the speed as 0
input_turning = (sampling_2_center - center_x) * base_impact # Calculating steering control signals
elif sam_1 and not sam_2: # If the target line is detected only at the upper sample line
input_speed = (line_track_speed / 3) # slow down
input_turning = 0 # No steering
else: # If neither sampling line detects the target line
input_speed = - (line_track_speed / 3) # backward
input_turning = 0 # No turning
# base.base_json_ctrl({"T":13,"X":input_speed,"Z":input_turning})
cv2.putText(line_mask, f'X: {input_speed:.2f}, Z: {input_turning:.2f}', (center_x+50, center_y+0), cv2.FONT_HERSHEY_SIMPLEX, 0.5, (255, 255, 255), 1)
# Visualization operations include drawing lines at the positions of the sampling lines, marking the sampling results, and displaying steering and velocity control signals
cv2.line(line_mask, (0, sampling_h1), (img.shape[1], sampling_h1), (255, 0, 0), 2)
cv2.line(line_mask, (0, sampling_h2), (img.shape[1], sampling_h2), (255, 0, 0), 2)
if sam_1:
# Draw green marker lines at the ends of the target line at the upper sample line
cv2.line(line_mask, (sampling_1_left, sampling_h1+20), (sampling_1_left, sampling_h1-20), (0, 255, 0), 2)
cv2.line(line_mask, (sampling_1_right, sampling_h1+20), (sampling_1_right, sampling_h1-20), (0, 255, 0), 2)
if sam_2:
# Draw green marker lines at the ends of the target line at the lower sampling line
cv2.line(line_mask, (sampling_2_left, sampling_h2+20), (sampling_2_left, sampling_h2-20), (0, 255, 0), 2)
cv2.line(line_mask, (sampling_2_right, sampling_h2+20), (sampling_2_right, sampling_h2-20), (0, 255, 0), 2)
if sam_1 and sam_2:
# If the target line is detected at both the upper and lower sample lines, draw a red line from the center of the upper sample line to the center of the lower sample line.
cv2.line(line_mask, (sampling_1_center, sampling_h1), (sampling_2_center, sampling_h2), (255, 0, 0), 2)
_, frame = cv2.imencode('.jpeg', line_mask)
display_handle.update(Image(data=frame.tobytes()))
if stopButton.value==True:
# picam2.close()
cv2.release() # If yes, close the camera
display_handle.update(None)
# Display the "Stop" button and start the thread that displays the function
# ================
display(stopButton)
thread = threading.Thread(target=view, args=(stopButton,))
thread.start()