Image and Telemetry Timestamps




Image and Telemetry Timestamps

Postby joma » Wed 13. Aug 2014, 08:00

Hello,
I just ran into the following scenario that to my understanding is caused by a missing timestamp for the images and the telemetry. A timestamp would give me the possibility to sychronize telemetry data with pictures.

The consequence of this can already be seen when launching the provided demo.

If I start the demo with
Code: Select all
/opt/euroc_c2s1/start_euroc_task_selector

and
Code: Select all
rosrun euroc_c2_demos euroc_c2_demo[b].py[/b]

to launch the Python version of the demo, I can see the target points in the tcp camera at nearly the same position all the time. Telling me at least that the delay seems to be more or less constant over the simulation time.

If I run the C++ version of the same demo by
Code: Select all
rosrun euroc_c2_demos euroc_c2_demo

the target points are spread over the whole picture, sometimes even are outside of the picture. This tells me that the delay from the time where the picture is taken to the time where the callback gets the picture is varying over the simulation time.

To my understanding this will make quite hard to solve the task with the conveyor belt as it will be quite hard to predict the point where the gripper has to grasp the object without knowing the actual time when the picture was taken.

Just adding a timestamp to the picture in the C++ callback will not solve this issue as we already could see in the provided C++ Demo.

Is there any way to get the camera and telemetry data in a more sychonized way?

Thanks

Johannes
joma
 
Posts: 12
Joined: Tue 29. Jul 2014, 15:15

by Advertising » Wed 13. Aug 2014, 08:00

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Re: Image and Telemetry Timestamps

Postby Peter Lehner » Wed 13. Aug 2014, 08:29

Hello Johannes,

I just ran into the following scenario that to my understanding is caused by a missing timestamp for the images and the telemetry. A timestamp would give me the possibility to sychronize telemetry data with pictures.


There are simulation timestamps available in both the image messages and the telemetry messages in the 'header' section. You can verify these while the simulation is running with:
$ rostopic echo /euroc_interface_node/telemetry/header/stamp
and
$ rostopic echo /euroc_interface_node/cameras/tcp_rgb_cam/header/stamp

Both stamps describe the actual time point when the telemetry / image is taken and should allow you to synchronize both.

Best

Peter
Peter Lehner
 
Posts: 53
Joined: Fri 27. Jun 2014, 14:33


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