[ros-users] Bag file recording / playback asynchronous in RViz

Tim Field tfield at willowgarage.com
Wed Sep 1 17:49:06 UTC 2010


On Wed, Sep 1, 2010 at 9:46 AM, Joel Cartwright <J.J.Cartwright at hw.ac.uk>wrote:

> ... would you have a problem with out of
> order messages with this script (from different publishers), and still
> need to sort them somehow?
>

I'm not sure what "sorting" means here.  Messages are stored in bags with a
timestamp.  That timestamp can be anything.  rosbag record subscribes to
topics and stores the message receipt time.  No matter how the timestamps
are written to the bag, the rosbag API (or rosbag play) will use the bag
index to return the messages in chronological order based on the stored
timestamp.

This script is changing the stored timestamp to be the Header timestamp.
 The order will differ if the publish order is not the same as the Header
timestamp order.  That's fine in Armin's use case of visualizing joint
states and laser scans.

There the transport hints sets UDP as a preference, and falls back to
> TCP with the 'no delay' option set.
>
> If you need reliable transfer, you could just try the tcpNoDelay option
> without the UDP hint.
>

In general, those are good suggestions.  I doubt TCP_NODELAY is the issue
here - Armin's publishing laser scans at 10 Hz and seeing delays on the
order of seconds.

Tim
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