Cedric Pradalier wrote:
> Hi,
>
> this discussion raised my curiosity, so I created a small test program 
> to evaluate the advantage of using shared memory. The program is quite 
> simple: on one end a publisher is creating an image of some size, and 
> publishing it with a timestamp given by ros::Time::now(), on the other 
> end, a receiver is receiving the image, and recording the difference 
> between ros::Time::now() and the image timestamp.
>
> I made this test for 1000 images, from 640x480x1, 640x480x3, 
> 1500x1000x3, 3000x2000x3. The results are summarised in the attached pdf.
>
> I also attach the test file so that someone can point out if something 
> is wrong in my test.
>
> The bottom line is: for big object, shared memory transfer reduces 
> significantly the delivery delay.
>
> I hope that helps.

I also add the variation of the reception interframe time in the plot, 
as delivery delay is not the only parameter affected by the type of 
transport.

Best

-- 
Dr. Cedric Pradalier
http://www.asl.ethz.ch/people/cedricp