[ros-users] Firewire camera synchronization

Dan Lazewatsky lazewatskyd at cse.wustl.edu
Tue Nov 30 16:36:53 UTC 2010

This isn't a particularly good solution, but (for now) you could write a
node that listens to both camera topics using the ApproximateTime
synchronizer (http://www.ros.org/wiki/message_filters/ApproximateTime), and
republishes the images with the same timestamp. I've done this do to stereo
with separate USB cams, and it works OK.


On Tue, Nov 30, 2010 at 4:12 PM, Jack O'Quin <jack.oquin at gmail.com> wrote:

> On Tue, Nov 30, 2010 at 6:56 AM, Thomas Moulard
> <thomas.moulard at gmail.com> wrote:
> > Hello everyone,
> > I would like to start by saying that I'm sorry to ask a question that
> > seems to be quite recurrent on this mailing-list
> > but I didn't find the information I am looking for.
> >
> > I am trying to run stereo_image_proc on two PointGrey Flea2 firewire
> > cameras connected on the same bus. There is no hardware (external)
> > trigger.
> > The camera documentation indicates it is possible to get synchronized
> > images from theses cameras in this precise configuration.
> >
> > However, it is currently not the case as I am launching two different
> > instances of camera1394_node to grab the images.
> >
> >
> > My questions are:
> >
> > 1. I would like to know what are the plans to support stereo pairs of
> > Firewire cameras?
> > I think many people use similar configurations and it is really a
> > shame that ROS does not work "out of the box" for this
> > as for all the components I have tested so far.
> >
> > 2. How should this problem solved?
> >
> > I don't see any way to make stereo acquisition work with separate
> > components doing the grabbing as this is done
> > currently. Should a camera1394_stereo_node be written? Is it how this
> > problem should be solved?
> There are three possible solutions outlined in this enhancement ticket:
>  https://code.ros.org/trac/ros-pkg/ticket/4217
> Currently, stereo image processing requires identical time stamps for
> the two stereo images. Running two separate mono versions of
> camera1394_node will not ensure that.
> The ticket suggests modifying image_pipeline to relax that requirement
> slightly. I don't know what the status of that request is. No
> committed fix is mentioned yet. I wonder whether it will be in
> Diamondback. I don't see any image_pipeline or stereo_image_proc
> reviews for that distribution yet. So, maybe it could still be done.
> As ticket #4217 said, one good option would be to create a stereo
> version of the driver, which could publish both images with the same
> time stamp. This could be done in time for Diamondback, if there's a
> consensus that it's needed. I don't mind doing the work, though I'd
> need to borrow or acquire a suitable pair of stereo cameras for
> testing.
> That was not one of the future enhancements identified during the
> C-turtle API review:
> http://www.ros.org/wiki/camera1394/Reviews/2010-05-27_API_Review#Conclusion
> Some time soon, we need to hold a review for Diamondback enhancements
> to camera1394. I'll announce that here when ready. Please participate
> if you can.
> Regards,
> --
>  joq
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