[ros-users] State of URDF

[Dave Coleman]

Greetings,

I'd like to update the ROS community on the current status of the Unified
Robotic Description Format (URDF). As ROS matures some packages are being
moved out of the ROS ecosystem into stand-alone projects. With URDF, this
has caused a number of package naming changes between Fuerte, Groovy, and
Hydro that have made the situation a little confusing, especially on the
ROS wiki.

I've made a *diagram* that outlines the current components of URDF and
shows how they work together:
http://www.ros.org/wiki/urdf#Components

*Current Status:*

1) The core URDF parser and data structures
(urdfdom<https://github.com/ros/urdfdom>,
urdfdom_headers <https://github.com/ros/urdfdom_headers>) have been pushed
upstream into stand alone (no ROS-dependencies) software packages that will
in the future be released into Ubuntu completely separate from ROS.

2) There is now a distinction between a URDF *file* and a URDF *data
structure*. A URDF file follows the XML format as described on the ros.org
wiki <http://ros.org/wiki/urdf/XML/>. A URDF data structure is a set of
generic classes that various formats (currently URDF and Collada) can be
parsed into.

3) A new plugin abstraction layer
(urdf_parser_plugin<https://github.com/ros/robot_model>)
allows the URDF data structures to be populated with various file formats
(currently URDF and Collada)

4) The ROS packages *urdf_parser *and *urdf_interface* have been deprecated
in Groovy and removed in Hydro.

5) As of today, urdfdom and urdfdom_headers have been moved to Github from
Bitbucket.

6) An update to the
<transmission><http://ros.org/wiki/urdf/XML/Transmission>element has
been made to the URDF spec that is a revisit of the old
pr2_mechanisms format generalized for all robots. It currently lives in the
new ros_control <http://ros.org/wiki/ros_control> package but should
soon<https://github.com/ros/urdfdom/issues/3>be moved into urdfdom.

*Related Topics:*

1) The Gazebo <http://gazebosim.org/> simulator can use either URDF or its
own (more feature-filled) SDF format.
SDFormat<https://bitbucket.org/osrf/sdformat>was also recently
released upstream into a stand alone software package
available in Ubuntu separate from ROS. SDFormat also currently contains a
copy of the URDF parser.

2) Very preliminary discussions have begun on the needs of URDF 2.0 and
potential merging of SDF and URDF. There are several significant
limitations in the current URDF specification that need to be addressed.
This is targeted for ROS-I or later.

*Links:*
https://github.com/ros/robot_model
https://github.com/ros/urdfdom*
*
https://github.com/ros/urdfdom_headers
https://bitbucket.org/osrf/sdformat
http://www.ros.org/wiki/urdf

Thanks to Ioan Sucan, John Hsu, and Wim Meeussen for their continued
maintenance and support of these urdf components.


I hope this helps clarify things for everyone!


Dave Coleman
Open Source Robotics Foundation | 251.463.2345 | davetcoleman.com
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