[ros-users] problem using TimeSynchronizer with two images

[Dan Lazewatsky]

Thanks Patrick,
What you brought up doesn't fix my problem, but does elucidate what's 
actually going on. It turns out that there are two problems I'm having:
1) The images are being published independently by two nodes, so they 
never have the same timestamp, and thus will never get matched up. Is 
there a way to give TimeSynchronizer a threshold so it will match two 
message that are close enough?
2) Based on #1, using the raw transport actually shouldn't work. The 
reason it currently does is because cvToImgMsg doesn't fill in the 
header, so all timestamps are 0. I can manually set the 
timestamps/headers before sending off the message, but isn't cv_bridge 
supposed to do this?

Thanks,
-Dan

On 3/12/10 9:22 PM, Patrick Mihelich wrote:
> Hi Dan,
>
> You might need to increase the size of the queues used by the 
> subscriber filters and/or the synchronizer. If those queues fill up, 
> messages can get bumped off before they form a complete synchronized set.
>
> For debugging purposes it can be useful to register another callback 
> to the subscriber filters, just so you know when they get any data. 
> I've attached some sample source code.
>
> "compressed" transport definitely should work with the time 
> synchronizer. "theora" will not work reliably because it seems the 
> plugin doesn't retain the timestamp of the original image. I've opened 
> a ticket <https://code.ros.org/trac/ros-pkg/ticket/3882> for that.
>
> HTH,
> Patrick
>
> On Fri, Mar 12, 2010 at 9:12 AM, Dan Lazewatsky 
> <lazewatskyd at cse.wustl.edu <mailto:lazewatskyd at cse.wustl.edu>> wrote:
>
>     Thanks, that did the trick. One thing I'm still having trouble
>     with is getting transports other than raw to work with
>     image_transport::SubscriberFilter. If I pass
>     image_transport::TransportHints th(transport) to
>     image_transport::SubscriberFilter, where transport is "compressed"
>     or "theora", I never seem to get any data. rxgraph -t shows that
>     my node is connected to my image publisher on the right topic, but
>     the callback never gets called.
>
>     Thanks,
>     -Dan
>
>
>     On 3/11/10 5:11 PM, Patrick Mihelich wrote:
>>     On Thu, Mar 11, 2010 at 2:55 PM, Dan Lazewatsky
>>     <lazewatskyd at cse.wustl.edu <mailto:lazewatskyd at cse.wustl.edu>> wrote:
>>
>>         On a related note, is there a way to use TimeSynchronizer
>>         with image_transport rather than subscribing to the image
>>         directly?
>>
>>
>>     Use image_transport::SubscriberFilter
>>     <http://www.ros.org/doc/api/image_transport/html/classimage__transport_1_1SubscriberFilter.html>
>>     as a drop-in replacement for message_filters::Subscriber. It uses
>>     an image_transport subscriber under the hood.
>>
>>     Cheers,
>>     Patrick
>>
>>
>>     _______________________________________________
>>     ros-users mailing list
>>     ros-users at code.ros.org <mailto:ros-users at code.ros.org>
>>     https://code.ros.org/mailman/listinfo/ros-users
>
>     _______________________________________________
>     ros-users mailing list
>     ros-users at code.ros.org <mailto:ros-users at code.ros.org>
>     https://code.ros.org/mailman/listinfo/ros-users
>
>
>
> _______________________________________________
> ros-users mailing list
> ros-users at code.ros.org
> https://code.ros.org/mailman/listinfo/ros-users
>    
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ros.org/pipermail/ros-users/attachments/20100315/97949fe7/attachment-0004.html>