[ros-users] Contact point definition in URDF format

Wim Meeussen meeussen at willowgarage.com
Fri Mar 2 18:41:52 UTC 2012


> here is another proposal to enhance humanoids robots support in ROS.
> When dealing with legged robots, one very important information is the
> list of valid contact zones, i.e. the zones which can safely support the robot.
> Information about soles are also required to generate walking trajectories.
> An example of this would be http://hal.inria.fr/docs/00/46/41/25/PDF/paper.pdf.
> I suggest adding to the <link> element of URDF an optional node
> called "contact" which structure is very close to the geometry and
> collision elements.

First of all, it's great you want to better support humanoid robots in
the ROS toolchain!  Our general philosophy with this type of
descriptions has been to create multiple small and special purpose
descriptions/parsers.  So instead of extending the URDF description
with more and more (optional) fields, different domains specify their
own description. For example, Gazebo specifies its own description for
sensors, etc.  Motion planning is another example with their SRDF

In the end it is perfectly fine if all these descriptions end up in
the same physical file (on the PR2 they all end up in
/etc/ros/urdf/robot.xml), as long as you have different parsers
extracting specific information from that single file.

So for the humanoid specific description, it's probably best to create
a new description/parser. So at least initially, you have the
flexibility to rapidly develop and modify the format. Once it
stabilizes and you have a good idea of the scope of this new
description format, we can discuss if it could make sense to fold it
into the URDF description, or to keep it as a separate description.

So, for example, part of your humanoid specific description could look
like the example below, where your description refers to elements in
the URDF description.

  <contact name="l_foot" link="name_of_the_urdf_link">
    <.... your specification of allowed contact points.../>


Wim Meeussen
Willow Garage Inc.

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