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.
* I also had some trouble finding this information.  It is defined in the
C++ API for laser_geometry::LaserProjection<http://www.ros.org/doc/api/laser_geometry/html/classlaser__geometry_1_1LaserProjection.html>.
I also added a link to this information on the
laser_assembler<http://www.ros.org/wiki/laser_assembler>page (which
I'm assuming you're using to generate the point clouds).

Hopefully this helps.
Vijay

On Sun, Jul 4, 2010 at 9:37 AM, Ken Conley <kwc@willowgarage.com> wrote:

> 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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