为什么 ROS 发布者不发布第一条消息?

Question

>我有一个发布者发布了两个主题为"图像"和"深度"的图像，还有一个订阅者在收听这两个主题。

发布者从两个文件夹中读取图像，并在同一循环中发布这两个文件夹。每个图像都有相应的深度，并且这两个图像使用相同的名称进行映射。发布速率为 1Hz。

订阅者未获取第一对图像。我试图转储订阅到文件夹的图像。发布的所有图像都将被转储，除了第一对图像。

这是发布者的代码

import rospy
from sensor_msgs.msg import Image
from cv_bridge import CvBridge
import cv2
import os

def talker():
    rospy.init_node('talker', anonymous=True)
    rate = rospy.Rate(1) # 1hz
    bridge = CvBridge()
    hello_str = "hello world %s" % rospy.get_time()
    rospy.loginfo(hello_str)
    path = "/home/test_img/"
    imglist = os.listdir(path)
    path_depth = "/home/out_depth/"

    for i in range(0,len(imglist)):
        topic = 'image'
        print(topic)
        pub = rospy.Publisher(topic, Image, queue_size=10)
        fn = path+imglist[i]
        print(fn)
        img = cv2.imread(fn)
        imgMsg = bridge.cv2_to_imgmsg(img, "bgr8")
        pub.publish(imgMsg)


        topic = 'depth'
        print(topic)
        pub = rospy.Publisher(topic, Image, queue_size=10)
        fn = path_depth+imglist[i]
        print(fn)
        img = cv2.imread(fn)
        imgMsg = bridge.cv2_to_imgmsg(img, "bgr8")
        pub.publish(imgMsg)
        rate.sleep()


if __name__ == '__main__':
    try:
        talker()
    except rospy.ROSInterruptException:
        pass

这是订阅者的代码

import rospy
import numpy as np
from sensor_msgs.msg import Image
from cv_bridge import CvBridge
import cv2
from datetime import datetime

def callback(data):

    bridge = CvBridge()
    # Convert your ROS Image message to OpenCV2
    cv2_img = bridge.imgmsg_to_cv2(data, "bgr8")
    cv2.imwrite('out_rgbd/'+datetime.now().strftime("%I:%M%S%f")+".jpg", cv2_img)
def listener():
    # In ROS, nodes are uniquely named. If two nodes with the same
    # name are launched, the previous one is kicked off. The
    # anonymous=True flag means that rospy will choose a unique
    # name for our 'listener' node so that multiple listeners can
    # run simultaneously.
    rospy.init_node('listener', anonymous=True)

    topic = 'image'
    print(topic)
    rospy.Subscriber(topic, Image, callback)
    topic = 'depth'
    print(topic)
    rospy.Subscriber(topic, Image, callback)
    # spin() simply keeps python from exiting until this node is stopped
    rospy.spin()
if __name__ == '__main__':
    listener()

执行发布器时，将列出所有图像(来自 print(fn( 行(。但是订阅者没有获得第一对图像。

我尝试使用"rosrecord"录制消息。它也没有获得第一对。

可能是什么原因？

Answer 1

尝试在初始化发布者时设置latch=True。
有关详细信息，请参阅 https://answers.ros.org/question/195348/about-subscriber-structure-and-latch-on-publisher/。