[ros-users] Sync problem with stereo_image_proc

[Sacha Aury]

I think that having a hardware solution is a bit overkill for my
problem. So I tried to write a node which collected image messages from
my two cameras and which published both message every x seconds,
typically 1/2. And when I am using image_pipeline/stereo_image_proc, I
got messages of that kind : 

[ WARN] 1274196325.866264000: [stereo_image_proc] Low number of
synchronized left/right image pairs received.
Left images received: 831
Right images received: 831
Synchronized pairs: 0
Possible issues:
	* The cameras are not synchronized.
	* The network is too slow. For each synchronized image pair, at most 1
is getting through.

I don't know what I could do more, since the synchronisation should be
done by a TimeSynchronizer in the stereo_image_proc class. Could it be
posible to cheat on the timestamps in any way ?

Thanks, and sorry for the double post, I made a mistake at first.

Le lundi 17 mai 2010 à 07:53 -0700, Gary Bradski a écrit :
> What level do you want synchronization on?  Within framerate (both
> frames happen randomly but within 1/30 of a second of each other) or
> exact frame synchronization? The first is achievable, the second needs
> extra hardware.
> 
> At most, ROS can get you timestamps to align to, but to get actual
> simultaneous frames, you'll need a triggering signal in hardware such
> as a wire between 2 cameras (that allow for this). Some 1394 cameras
> may allow triggering over the 1394 bus and then you'll only have the
> problem of getting both buses to trigger at the same time ... which
> may be approximately possible, most of the time ... on average.
> Depends on the driver and the 1394 port. 
> 
> I've seen an automotive 1394 article (not ROS related) where they have
> about 10 cameras. The cameras run the cameras at very high framerates
> and then they do timestamp synchronization which allows fairly
> synchronous alignment of multiple with no extra hardware.
> 
> Gary
> 
> On Mon, May 17, 2010 at 5:23 AM, Sacha Aury <sacha at shadowrobot.com>
> wrote:
>         Hi,
>         
>         I am trying to make a stereo camera acquisition using ROS with
>         the
>         cameradc1394 driver and the stereo_proc package. I've got a
>         separate
>         computer to stream the image_raw from my two cameras. The
>         stream works,
>         but when I launch stereo_image_proc, it seems that my two
>         cameras are
>         not synchronized :
>         
>         [ WARN] 1274098675.074074000: [stereo_image_proc] Low number
>         of
>         synchronized left/right image pairs received.
>         Left images received: 3079
>         Right images received: 3076
>         Synchronized pairs: 0
>         Possible issues:
>                * The cameras are not synchronized.
>                * The network is too slow. For each synchronized image
>         pair, at most 1
>         is getting through.
>         
>         Here is my launch file :
>         
>         <!-- startstream.launch  -->
>         <launch>
>                <param name="display" type="int" value="0"/>
>                <param name="framerate" type="double" value="15"/>
>                <param name="mode" value="MODE_320x240_YUV422"/>
>         
>          <node name="camera_left" pkg="cameradc1394"
>         type="cameradc1394"
>         respawn="true">
>                <param name="prefix" type="string"
>         value="/stereo/left/"/>
>                <param name="cameraindex" type="int" value="0"/>
>          </node>
>         
>         
>          <node name="camera_right" pkg="cameradc1394"
>         type="cameradc1394"
>         respawn="true">
>                <param name="prefix" type="string"
>         value="/stereo/right/"/>
>                <param name="cameraindex" type="int" value="1"/>
>          </node>
>         
>         </launch>
>         
>         Is there any specific way to make the two cameras
>         synchronize ?
>         
>         I am following that tutorial :
>         
>         http://www.ros.org/wiki/stereo_image_proc
>         
>         Thank you for any help.
>         
>         Sacha
>         
>         
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