How to support multiple robots with tf2

edit

Yes, relaying is really not very nice.

However I wouldn't know of any other way.

Note btw that you wouldn't necessarily need to write a new node. The transform node from topic_tools could be used for this (as you're just changing the frame_id).

But then it still leaves the problem that when you map back to the global /tf, you have frame names that are prefixed and not compatible with the urdf file as is. So I see in that code that I can add a prefix to the URDF like for the UR10. If I modify the urdf like that I can do it without relay, but then I'll have multiple robot descriptions around, which I guess is ok. Or is there another way of dealing with the prefixed frame_ids?

Even with tf_prefix you have to make sure your URDF (or: .xacro) matches the TF frames. I'm not sure how that would be different now?

But then it still leaves the problem that when you map back to the global /tf, you have frame names that are prefixed and not compatible with the urdf file as is

If a node operates on one robot then its tf topics should be remapped to /alice/tf and /alice/tf_static too. For example, maybe each robot gets its own robot_state_publisher instance on /alice and /bob. A tool only needs to be aware of the prefixed frame ids if it needs to operate on both robots at the same time.

but then I'll have multiple robot descriptions around,

It's possible to reuse the same description for both robots. That said, if there are multiple robots then it sounds reasonable to have multiple robot descriptions.

So then either an xacro or multiple urdf files with unique link names are a part of the recommended solution for this problem? If I wanted to put two UR10 robots in the same rviz session. With the xacro, I would use the ${prefix} option, for /tf frame_ids like alice/base_link and bob/base_link. If I use two urdf files that are calibrated for example, I'd need to have all my link names in those urdf files unique.