I dont receive any data from the sensors even thought publishers and subscribers are established

[kostakis04]

Hello,
I migrated from CARLA 0.9.15 with the external ros-bridge to CARLA 0.9.16, which provides native ROS2 support. The simulator launches successfully with the --ros2 option, and the provided ros2_native.py example correctly spawns a vehicle together with RGB camera, LiDAR, GNSS, and IMU sensors.

The ROS2 topics are successfully created and are visible from the ROS2 Jazzy Docker container. Also inspection of the CARLA actors confirms that all sensors are enabled for ROS.

Using ROS2 diagnostic tools, i notice that:

DDS discovery is working correctly,
and publisher and subscribers are established.

However, although publishers and subscribers discover each other successfully, no sensor messages are actually transmitted. Commands such as ros2 topic echo and ros2 topic hz rprint nothing without receiving any data.

I suspected that my docker is poorly created but i have been drained of ideas on how to fix this issue.

Thanks for you time and for any help in advance.

[farfromexact]

Discovery only proves that the ROS 2 graph can see the endpoints; it does not prove that the subscriber QoS, network path, and simulator tick are compatible. With native CARLA ROS 2, I would check the following in order:

• run ros2 topic info -v on one camera topic and compare publisher and subscriber QoS, especially reliability and durability
• try ros2 topic echo with the sensor's offered QoS or a best-effort override, since image and LiDAR streams commonly use best effort
• confirm ROS_DOMAIN_ID and RMW_IMPLEMENTATION are the same inside CARLA and the Jazzy container
• use host networking or explicitly allow DDS discovery and data traffic; discovery can work while data ports are blocked
• verify the world is ticking, especially if synchronous mode is enabled; a synchronous world needs a client to call world.tick or apply_batch_sync before sensors publish the next frame
• check the exact topic type and the native 0.9.16 example's topic names

The useful capture is ros2 topic info -v plus one topic echo with the selected QoS, the CARLA launch flags, RMW implementation, network mode, and whether the world is synchronous. That will separate a DDS QoS mismatch from a blocked data path or a simulation that is simply not advancing.

[kostakis04]

Thanks for the fast response.
I found out it was actually a poor communication part between my HOST and the Docker.
So, in order to combat the issue, i fixed the docker file volumes to mount the entire carla simulator.
By doing this, the docker and the carla simulator started communicating and the echo commands and the subscribers started working.