[ros-users] image transport python bindings

[Dan Lazewatsky]

Thanks for the update. I haven't played around with republishing too  
much, but I'll give it a shot again and see how it works.

-Dan
On Jun 21, 2010, at 6:36 PM, Patrick Mihelich wrote:

> Hi Dan,
>
> On Mon, Jun 21, 2010 at 10:29 AM, Dan Lazewatsky <lazewatskyd at cse.wustl.edu 
> > wrote:
> I was wondering what the status of the python bindings for
> image_transport is.
>
> There hasn't been any serious work on Python bindings for  
> image_transport.
>
> They would definitely be nice to have, but actually writing them  
> presents some thorny technical issues. Either you need to write pure- 
> Python analogues of image_transport *and* all plugins, or find a way  
> to wrap the C++ implementation and reuse the existing plugins. The  
> latter approach seems more attractive in terms of code reuse and not  
> increasing the burden on plugin implementers; but it requires  
> changing the plugin interfaces to abstract away explicit use of  
> roscpp (NodeHandle), as that won't play nice with rospy in the same  
> process.
>
> In short: this is all possible, just unpleasant and time-consuming.  
> Since dropping in an extra republish node works adequately, I  
> haven't made it a priority.
>
> I've been limping along either using C++ or subscribing directly to
> image messages in python, but it's starting to become a problem. The
> republish idea on the wiki doesn't seem like a particularly good
> solution.
>
> Sometimes it is actually the best solution! If the image topic is  
> published on machine A and there are multiple subscribers on a  
> machine B, republishing the images in raw format on machine B  
> minimizes both network bandwidth and CPU usage.
>
> For the one-to-one case - only one subscriber on the second machine  
> - it's true that spinning up a republish node is an inconvenience  
> and adds a little latency. I'd suggest adding it to your subscriber- 
> side launch file.
>
> Cheers,
> Patrick
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