add note for ros2 topic hz/bw.

[fujitatomoya]

part of ros2/ros2cli#843 (comment)

aligns with ros2/ros2cli#987

[fujitatomoya]

adding the same notice that says this is what you can see on your subscription, not publisher statistics

[fujitatomoya]

@ahcorde can you review this?

[github-actions]

HTML artifacts: https://github.com/ros2/ros2_documentation/actions/runs/13845274942/artifacts/2749105230.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
3. Open html-artifacts-5087/index.html in your favorite browser

[christophebedard]

Should the notes explicitly also say that the rate/bandwidth reported by the tools can therefore be misleading?

Example:

... and may not exactly match the publisher's rate/bandwidth. Therefore, the reported value may be misleading.

[fujitatomoya]

Should the notes explicitly also say that the rate/bandwidth reported by the tools can therefore be misleading?

i am not sure about this. on the subscription statistics with platform, network constraints and QoS configuration, this is what they can get. that actually sounds true for me, so maybe not misleading??? 🤔🤔🤔

[christophebedard]

It's true, but it's misleading if they think it represents the publisher rate/bandwidth. I was wondering if it would be worth it to explicitly mention that this is not the publisher rate, on top of saying that this actually represents the subscription's reception rate. This way, it's more explicit and hopefully clearer, especially since the ros2 topic hz section still says:

You can also view the rate at which data is published using:

It's kind of the difference between saying "this does X" and saying "this does X and not Y," if that makes sense.

[christophebedard]

Oh, I kind of missed the last part of the note

and may not exactly match the publisher rate.

Nevermind then, this is good 😅