[ros-users] topic vs tf

[Jeff Rousseau <jrousseau@aptima.com>]

One particular use case where a tf-only solution would break down is when you need to share geometric data between robots over a lossy connection (802.11b/g/a, zigbee, etc.)  In a multi-robot use case it is usually infeasible to have a single master, so instead you run a master locally on each robot and forward only the pertinent topics that other robots need access to for whatever particular problem they're trying to solve--since /tf is high-bandwidth you have to resort to sharing geometric topics.

> -----Original Message-----
> From: ros-users-bounces at code.ros.org [mailto:ros-users-
> bounces at code.ros.org] On Behalf Of Thibault Kruse
> Sent: Friday, December 09, 2011 12:14 PM
> To: User discussions
> Subject: [ros-users] topic vs tf
> 
> Hi,
> 
> I am keen on reading an answer to this answers.ros.org question:
> http://answers.ros.org/question/2803/when-should-i-send-geometric-
> information-over-a
> "When should I send geometric information over a topic as opposed to TF?"
> 
> I would think that TF is the best place to publish frames, meaning coordinate
> systems to be used as a point of reference for other geometric data.
> 
> So this would be ideal for robot joints/links, sensor coordinate systems, and
> perceived joints/links of other agents (humans or robots).
> 
> If possible, all those should rather be published in TF rather than anything
> else, I would believe.
> 
> However I do not yet understand whether there is a downside to using TF, or
> some kind of degradation when plenty of frames are being published.
> 
> The only thing I can think of is that rosbag and rxbag cannot treat individual
> transforms, they can only record / replay the whole tf tree.
> 
> Also I guess that data with a lot of noise is not suitable as a reference frame
> for anything, so there is no point in publishing that in TF.
> 
> Other thoughts?
> 
> cheers,
>    Thibault
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