[ros-users] Firewire camera synchronization

[Jack O'Quin]

On Thu, Dec 2, 2010 at 8:07 PM, Thomas Moulard <thomas.moulard at gmail.com> wrote:
> On Fri, Dec 3, 2010 at 2:54 AM, Jack O'Quin <jack.oquin at gmail.com> wrote:
>> Since two cameras on the same bus are synchronized automatically, it
>> may just work, even with separate processes.
>
> As long as you synchronize the acquisition with some interprocess locking.
> The context switch may also introduce a delay between the two acquisitions.
>
>> Just to see what happens, could you try running two driver nodes each
>> connected to a single camera? Capture some images in a bag and check
>> the timestamps when they are published. That is easy to do with
>> "rxbag".
>
> They are close but not identical (nsec are different).

Looks like it's working fine in the bag you captured. The differences
between frame times are in tens of microseconds, better than the 125
usec maximum deviation claimed by Point Grey.

The camera drivers are not doing any synchronization, it's provided by
the bus. Note that this synchronization would not happen if the
cameras were attached to different 1394 buses.

This is close enough for stereo processing. Since the time stamps are
not identical, our current stereo_image_proc rejects them. But, the
proposed approximate time stamp matching ought to work great for this
device.

I would expect about the same results with a nodelet implementation.

Thanks for running the test...
-- 
 joq