如何使用 Python 在 ROS 中订阅两个图像主题

Question

我正在尝试从车辆读取左右摄像头图像以进行一些图像处理。我不确定如何使用相同的回调函数来处理每个图像。我已经看到 where the data type was different, but not where both are of the same type, such as images. In this example，使用了单独的回调。

这是我目前的尝试：

import rospy
import cv2
import os
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image
import message_filters

def read_cameras():
    imageL = rospy.Subscriber("/camera/left/image_raw", Image, image_callback)
    imageR = rospy.Subscriber("/camera/right/image_raw", Image, image_callback)
    # Synch images here ? 
    ts = message_filters.ApproximateTimeSynchronizer([imageL, imageR], 10)
    rospy.spin()
    
def image_callback(imageL, imageR):
    br = CvBridge()
    rospy.loginfo("receiving frame")
    imageLeft = br.imgmsg_to_cv2(imageL)
    imageRight = br.imgmsg_to_cv2(imageR)
    # Do some fancy computations on each image
    
if __name__ == '__main__':
    try:
        read_cameras()
    except rospy.ROSInterruptException:
        pass

此外，即使看了documentation on approximate time synchronization，我仍然不明白我需要输入的参数。每个摄像头都应该以 24fps 的速度输出图像。

Answer 1

每个节点都需要先初始化自己，然后才能使用 rospy.init_node().

与 ROS 网络交互

此外，您需要提供两个 message_filter.Subscriber 而不是 rospy.Subscriber 到 message_filter.ApproximateTimeSynchronizer。最后，不要为每个订阅者设置回调，而应该使用 registerCallback.

为 ApproximateTimeSynchronizer 设置一次

这是一个工作示例：

#! /usr/bin/env python2

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

def read_cameras():
    imageL = message_filters.Subscriber("/camera/left/image_raw", Image)
    imageR = message_filters.Subscriber("/camera/right/image_raw", Image)

    # Synchronize images
    ts = message_filters.ApproximateTimeSynchronizer([imageL, imageR], queue_size=10, slop=0.5)
    ts.registerCallback(image_callback)
    rospy.spin()

def image_callback(imageL, imageR):
    br = CvBridge()
    rospy.loginfo("receiving frame")
    imageLeft = br.imgmsg_to_cv2(imageL)
    imageRight = br.imgmsg_to_cv2(imageR)
    # Process images...

if __name__ == '__main__':
    rospy.init_node('my_node')
    try:
        read_cameras()
    except rospy.ROSInterruptException:
        pass

请务必检查您的 ApproximateTimeSynchronizer 的延迟 (slop) 并根据您的数据进行设置。

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