Along these lines, I know how to do software triggering (in theory) for
lib1394, so I could add that to the camera1394 node (along with
configuration options to connect to and publish data from multiple
cameras that will be sync'ed. But, this won't be for a while.
I noted that roscpp latest has a new feature in message_filters for
ApproximateTime syncing, that adapts as needed to syncing multiple
incoming messages. Unfortunately, rospy doesn't implement this, so it's
not a simple line edit to fix the calibration package, which uses rospy.
Patrick Mihelich wrote:
> On Tue, Apr 6, 2010 at 5:43 PM, Eric Perko <wisesage5001@gmail.com
> <mailto:wisesage5001@gmail.com>> wrote:
>
> are your image_raw topics
> synced? I'm trying to use two individual cameras, but because each one
> gets its own camera1394 node, I don't think their timestamps will ever
> really be in sync even with external triggering or some other
> guarantee I can make about the frames themselves matching up.
>
>
> This is most likely the problem. The stereo camera calibrator only
> subscribes to the image topics, not camera_info, but it does expect the
> left and right images to be synchronized. The wge100_camera driver goes
> to some trouble to support synching two cameras with an external
> trigger, and of course this is easy with a unified stereo camera that
> does the triggering for you.
>
> The more lax case of trying to use two unsynchronized cameras for stereo
> isn't directly supported by the image_pipeline right now.
> message_filters is gaining support for approximate time synchronization,
> so maybe I should target that for the next image_pipeline release. It's
> better to have the cameras synchronized, but clearly that poses some
> technical problems.
>
> A hacky workaround would be to write a relay node that listens to the
> left and right image topics, matches up pairs that are close enough, and
> republishes them with the same timestamp.
>
> What is the behavior of the stereo camera calibrator if the left and
> right image topics are not sycned up? Does it just hang waiting for a
> synchronized pair?
>
>
> Yep...
>
> If so, it might be really helpful to get some sort
> of warning that the two image topics are out of sync and therefore
> will not be used.
>
>
> I opened ticket 3962 <https://code.ros.org/trac/ros-pkg/ticket/3962>.
>
> Patrick
>
>
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