CODEWITHSUNDEEP
pythonopencvdelayrosrospy
Aviationman
Aviationman

Reputation: 1

How to get consecutive images with a delay between using rospy.Subscriber

I am trying to read two consecutive images from my rostopic using rospy.Subscriber to compare the orientation between these pictures but using the code below, I found out, two images I get are the same every time, so I am trying to find out if there is a way to get the two images with delay, more specifically, getting the second image 3 seconds after I get the first image. I tried putting time.sleep() between functions but it wouldn't work out.

Thanks for the help. Aviationman

import cv2
import numpy as np
import rospy
import time
import os


from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError

def cam_callback(msg):
          path = '/home/furki/img'
          try:
     # Converting ROS Image message to OpenCV2
             cv2_img1  = bridge1.imgmsg_to_cv2(msg,"bgr8")
          except CvBridgeError as e:
             print(e)
          else:
          # Save your OpenCV2 image as a jpeg
             img1 = cv2.imwrite(os.path.join(path, f'img1.jpeg'), cv2_img1)

def cam_callback2(msg):
          path = '/home/furki/img'
          try:
     # Converting ROS Image message to OpenCV2
             cv2_img2 = bridge.imgmsg_to_cv2(msg,"bgr8")
          except CvBridgeError as e:
             print(e)
          else:
          # Save your OpenCV2 image as a jpeg
             img2 = cv2.imwrite(os.path.join(path, f'img2.jpeg'), cv2_img2)


rospy.init_node("orientation_feature_detection_py")
image_topic = '/s500/usb_cam/image_raw'
rate = rospy.Rate(1)


rospy.Subscriber(image_topic, Image, cam_callback)
rate.sleep()
rospy.Subscriber(image_topic, Image, cam_callback2)
rate.sleep()

# Reading the two images

img1 = cv2.imread('/home/furki/img/img1.jpeg')

img2 = cv2.imread('/home/furki/img/img2.jpeg')

Upvotes: 0

Views: 134

Answers (1)

BTables
BTables

Reputation: 4843

Making two subscribers doesn't really do anything here. They will be called every time a new message is received on the topic. If you want to limit how often you're processing images you should cache the image and use a run loop:

latest_msg = None
def cam_callback(self, msg):
    global latest_msg
    latest_msg = msg.data


if __name__ == '__main__':
    rospy.init_node('some_node')
    sub = rospy.Subscriber('/img_topic', Image, cam_callback)

    rate = rospy.Rate(1/3)
    while not rospy.is_shutdown():
        #process image here
        rate.sleep()

Upvotes: 1

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