Hi,
you are right, this behavior seems somehow odd. I guess the reason is
that on the PR2, the TF tree looks like this:
/map -> odom_combined -> base_footprint -> ...
As far as I know, Pr2Odometry is set up to not publish transforms at
all, just Odometry messages. These are read by the robot_pose_ekf node
which then publishes the odom_comined -> base_footprint transform. If
you want to use the Pr2Odometry node for doing it, I think you might
need to fork and hack it. This should not be too hard however.
Lorenz
> Hi all,
>
> I am using the controller Pr2Odometry from the
> pr2_mechanism_controllers package to do simulated odometry for the
> KUKA YouBot in Gazebo. I am seeing an oddity in the tf tree, and
> I'd like to find out whether it's something I'm doing. It seems to
> me that there is a reversed parent/child relationship in the tf
> links published by Pr2Odometry. The documentation for it at
>
> http://www.ros.org/wiki/pr2_mechanism_controllers/Pr2Odometry#ROS_API
>
> says
>
> /tf (tf/tfMessage)
> Two transforms are published to tf, a constant transform from
> the base_footprint frame to the base_link frame and the transform
> from the odom frame to the base footprint frame.
>
> This conforms to my expectation, which is that /odom is the parent
> of /base_footprint. Thus, if global localization drops out, you can
> still continue on odometry alone for as long as your dead reckoning
> will allow. This expected behavior is also compatible with
> fake_localization, which publishes a transform from /map to /odom.
>
> By contrast, examining tf on the running system shows me a tree in
> which /base_footprint is at the root. /odom is a leaf and a sibling
> of /base_link, which connects to the rest of the tree. The code at
>
> /opt/ros/electric/stacks/pr2_controllers/pr2_mechanism_controllers/src/pr2_odometry.cpp
>
> is clear:
>
> out.header.frame_id = tf::resolve(tf_prefix_,base_footprint_frame_);
> out.child_frame_id = tf::resolve(tf_prefix_,odom_frame_);
>
> So /odom is the child here. This behavior seems to contradict
> intuition and the (admittedly terse) documentation online. However,
> since I am using this pr2 code on the YouBot, I wonder if there is
> something different about how the PR2 operates?
>
> Thanks!
>
> -ross
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--
Lorenz Mösenlechner | moesenle@in.tum.de
Technische Universität München | Karlstraße 45
80335 München | Germany
http://ias.cs.tum.edu/ | Tel: +49 (89) 289-26910
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