No `cmd_vel` topic when using diff_drive

[anticitizn]

Environment

• OS Version: Linux Mint 21.3 (aka Ubuntu Jammy)
• Source or binary build? Binary, Gazebo Garden 1.0.0-1~jammy

Description

• Expected behavior: Running the diff_drive.sdf example world, I expect to see the odometry, tf, and cmd_vel topics
• Actual behavior: Only odometry and tf are visible.

I only noticed this after upgrading all of my packages today - not sure if related, but I am confident this example used to work on my computer a few days ago.

Output

danny@danny-desktop:~$ gz topic -l
/clock
/gazebo/resource_paths
/gui/camera/pose
/model/vehicle_blue/odometry
/model/vehicle_blue/tf
/model/vehicle_green/odometry
/model/vehicle_green/tf
/stats
/world/diff_drive/clock
/world/diff_drive/dynamic_pose/info
/world/diff_drive/pose/info
/world/diff_drive/scene/deletion
/world/diff_drive/scene/info
/world/diff_drive/state
/world/diff_drive/stats

[anticitizn]

Okay I'm a bit stupid, it does actually work and listens to the messages published on cmd_vel but the topic is not listed by gz topic -l. Is that the intended behavior? I feel like before the topic was in the list. Sorry if this is something obvious.

[francocipollone]

Okay I'm a bit stupid, it does actually work and listens to the messages published on cmd_vel but the topic is not listed by gz topic -l. Is that the intended behavior? I feel like before the topic was in the list. Sorry if this is something obvious.

The discovery only works for published topics. This is due to the underlying transport protocol being used (zeromq).

If I recall correctly I think it is in the roadmap to also discover subscriptions.

[anticitizn]

Thank you, it's a layer 8 problem then.

[francocipollone]

Thank you, it's a layer 8 problem then.

I just skimmed a bit the changelog and it seems it is a feature added in gazebo harmonic. 😃