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@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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