Camera topic has no publishers with ROS2

[JohnBrann]

Hello,

I am trying to test the local_client on my machine to get more comfortable with ManipulationNet.

I have just did a fresh install of Ubuntu 24.04 and ROS2 Jazzy, as well as all of the other installation requirements for ManipulationNet.

After building and sourcing my workspace I run ros2 run mnet_client local_test to which I get

I am running this node in a seperate terminal for the camera:
ros2 run usb_cam usb_cam_node_exe --ros-args -r /image_raw:=/image_raw -r /camera_info:=/camera_info

This is what my team_config .json looks like:
{ "team_unique_code": "TEST1234", "camera_image_topic": "/image_raw", "camera_info_topic": "/camera_info", "file_dir": "/home/csrobot/mnet_local_test", "autonomy_level": 1 }

Am not sure if I am missing something in the documentation? Has mnet been tested on 24.04 or ROS2 Jazzy?

Thank you!

[c-yiting]

Hi,

Yes, mnet client supports 24.04 and ROS2 Jazzy. For local testing, your team_config.json is OK.

It seems your system is not publishing content to the input ROS image topic so the mnet client raised the error. It is recommended to first use RViz to visualize and verify that the input image topic is correct.

If your image topic is verified working, please try ros2 run mnet_client local_test multiple times, as sometimes there could be possible delays for the client to detect the published images.

[JohnBrann]

Thank you for the response!

From my current image publishing method I was able to subscribe to that topic in rviz2 and get the camera feedback. I was also able to create my own subscriber that can visualize the images on that topic.

When I ran it with the local test client I was still getting issues as shown above. To temporarily get around this I commented out the "self.topic_has_publishers()" check in base_client.py. I was then able to proceed with the rest of the local_test and everything worked as intended.

I am not sure what the issue is but it has something to do this the function "self.get_publishers_info_by_topic(self.camera_topic)" always returning an empty list even when I would do "ros2 topic list" and see my topic being published (weird).

I also tried just running the local client multiple times but continued to get the same issue.

Everything is working as expected now but I will keep trying without commenting that function. I suspect something with my system or ROS2.

Thank you!

[c-yiting]

Thank you for bringing this up!

This issue is caused by ROS 2's asynchronous discovery mechanism. The self.get_publishers_info_by_topic() method queries the local graph cache, which is updated only while the ROS node is spinning.

I have updated the code to fix this issue by adding a spin_once call before checking the publishers.

        rclpy.spin_once(self, timeout_sec=0.5) # spin once to update publisher info
        publishers = self.get_publishers_info_by_topic(self.camera_topic)

Please let me know if you have further questions.