Published message is not received

[vvigilante]

Hello! Tested with ROS melodic on Ubuntu 18.04

rostopic info shows that the topic is published and subscibed as expected. rostopic hz shows that the topic is being published with a frequency of ~10hz, as expected. rostopic echo is completely silent, so is the subscriber node that I wrote.

It works if I change the type of the published topic to String or to Image or to Pose2D, it does not work with Detection2D or Detection2DArray or BoundingBox2D.

My code looks like this:

    from time import sleep
    import rospy
    rospy.init_node('t1')
    pub = rospy.Publisher('detection', Detection2DArray, queue_size=10)
    while True:
        message = Detection2DArray()
        pub.publish(message)
        sleep(0.1)

[Kukanani]

Please post the code of the non-working subscriber and the exact commands you are running in your terminal. Thanks

On Fri, Oct 9, 2020 at 08:35 Vincenzo notifications@github.com wrote:

Hello! Tested with ROS melodic on Ubuntu 18.04

rostopic info shows that the topic is published and subscibed as expected. rostopic hz shows that the topic is being published with a frequency of ~10hz, as expected. rostopic echo is completely silent, so is the subscriber node that I wrote.

It works if I change the type of the published topic to String or to Image, it does not work with Detection2D or Detection2DArray

My code looks like this:

from time import sleep
import rospy
rospy.init_node('t1')
pub = rospy.Publisher('detection', Detection2DArray, queue_size=10)
while True:
    message = Detection2DArray()
    pub.publish(message)
    sleep(0.1)

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[vvigilante]

Thank you for your answer. Here is the list of the commands:

rostopic list
rostopic hz /detection
rostopic bw /detection
rostopic echo /detection

rostopic info detection

gives

Type: vision_msgs/Detection2DArray

Publishers: 
 * /t1 (http://ubuntu:46019/)

Subscribers: 
 * /t2 (http://ubuntu:35623/)

The code for the subscriber is the following.

import rospy
from vision_msgs.msg import Detection2DArray

rospy.init_node('t2')

def rcv_detection(msg):
    rospy.loginfo('detection here')

sd = rospy.Subscriber("detection", Detection2DArray, rcv_detection)
rospy.spin()

It stays completely silent.

[Kukanani]

The code you posted is incomplete. Your publisher does not import Detection2DArray.

In general, if rostopic hz works and rostopic echo does not, this is probably an issue with your machine setup or network transport, not the message type itself. I would investigate other issues such as

• your ROS environment variables (ROS_IP or ROS_HOSTNAME are common problems)
• checking that both terminals have sourced the workspace with vision_msgs in it
• checking that you can run an interactive python interpreter and import vision_msgs
• machine setup (are you running these nodes on different machines or do you have a remote master?)
• roswtf
• computer networking configuration

I was unable to reproduce the bug on ROS melodic, Ubuntu 18.04, latest vision_msgs on melodic-devel branch, using the following code. I get continuous detection here log messages on the subscriber. I verified that the following example works on both my own desktop machine and in a ros:melodic docker container. Therefore, I am going to close the issue as wontfix since it does not appear to be a problem with this package. If you find more detailed information that specifically points to this package as the issue. If you install another third-party messages library, does that one work using the same code?

Note that because you do not check for the rospy.is_shutdown() state, it is "difficult" to kill publisher (Ctrl-/ not Ctrl-C in bash)

publisher

#!/usr/bin/python

from time import sleep
import rospy
from vision_msgs.msg import Detection2DArray

rospy.init_node('t1')
pub = rospy.Publisher('detection', Detection2DArray, queue_size=10)
while True:
    message = Detection2DArray()
    pub.publish(message)
    sleep(0.1)

subscriber

#!/usr/bin/python

import rospy
from vision_msgs.msg import Detection2DArray

rospy.init_node('t2')

def rcv_detection(msg):
    rospy.loginfo('detection here')

sd = rospy.Subscriber("detection", Detection2DArray, rcv_detection)
rospy.spin()

[vvigilante]

Dear Kukanani, thank you for your help.

roswtf gives

ERROR The following nodes should be connected but aren't:
 * /t1->/t2 (/detection)

Setting ROS_ID=127.0.0.1 does not help.

The problem only happens if I apt install ros-melodic-vision-msgs.

If I clone the repository, checkout melodic-devel and catkin build, everything works as expected