For data like this, it's best to use the libraries that come with ROS
to process the data. The data you see is from the tf library, which
has tutorials here:

http://www.ros.org/wiki/tf/Tutorials

I also recommend following the ROS tutorials:

http://www.ros.org/wiki/ROS/Tutorials

In particular, recording and playing back data:

http://www.ros.org/wiki/ROS/Tutorials/Recording%20and%20playing%20back%20data

You shouldn't have to 'parse' the ROS bag file. ROS bag file data can
be treated identically to the original source of data, so if you write
a node in ROS that subscribes to this data, you simply have to play
the recorded bag data into it to get the same result.

Hope this helps,
Ken

On Sun, Jul 4, 2010 at 9:31 AM, j2eegirl <dp@zju.edu.cn> wrote:
>
> My advisor gave me a bag file for a pr2 robot, which includes three kinds of
> topic, namely sensor_msgs/pointcloud, sensor_msgs/pointcloud2 and
> tf/tfmessage.
> I want to get the robot motion information and the obstacle position
> information. From the tf document I can get two kinds of information. One
> kind is of a tree  to introduce the relationship of different links. But the
> other kind like this:
> transforms
>        [0]
>                header
>                        seq: 0
>                        stamp: 1274768649205000409
>                                secs: 1274768649
>                                nsecs: 205000409
>                        frame_id: /odom_combined
>                child_frame_id: /base_footprint
>                transform
>                        translation
>                                x: 2.12986805655
>                                y: -0.140524320055
>                                z: 0.0
>                        rotation
>                                x: 0.00490979815527
>                                y: 0.00847065476276
>                                z: 0.721995381834
>                                w: 0.691828599077
> I want to know  how to use the translation and rotation operations.
> Another question is about the sensor_msgs/pointcloud topic. In the
> sensor_msgs/pointcloud document, I don't know how to use the index, distance
> and timestamp channel. I want to know how to find the help document.
> Thank you.
> --
> View this message in context: http://ros-users.122217.n3.nabble.com/How-to-parse-the-bag-file-tp942523p942523.html
> Sent from the ROS-Users mailing list archive at Nabble.com.
>
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