[ros-users] Draft REP: Coordinate Frames for Humanoids Robots

[Thomas Moulard]

Hi all,
Attached is a draft defining naming conventions and semantic meaning
for coordinate frames of legged robots used within ROS.

The HTML version is available here:
http://laas.github.com/rep-coordinate-frames-for-biped-robots/rep-0118.html

If this interests you, consider voting (voting guidelines are
documented in REP 10
here: http://www.ros.org/reps/rep-0010.html).

Best regards,
-- 
Thomas Moulard
-------------- next part --------------
REP: 118
Title: Coordinate Frames for Humanoids Robots
Version: $Revision: 1 $
Last-Modified: $Date: 2012-01-11 11:53:00 +0200 (Wed, 11 Jan 2012) $
Author: Thomas Moulard <thomas.moulard at gmail.com>
Status: Draft
Type: Informational
Content-Type: text/x-rst
Requires: 103, 105
Created: 25-Nov-2011
Post-History:

Abstract
========

This REP specifies naming conventions and semantic meaning for
coordinate frames of humanoids robots used within ROS.

Motivation
==========

Developers of packages aimed at humanoids robots need a shared
convention for coordinate frames in order to better integrate and
re-use software components.

The REP 105 [2] already defines frames for mobile bases. This REP
both remains compatible with REP 105 [2] and extends it to label other
important locations on a humanoid robot such as the gaze (head), left
and right wrists, hands and feet.


Specification
=============

Coordinate Frames
-----------------

base_link
'''''''''

The coordinate frame called ``base_link`` is rigidly attached to the
robot root body. It is recommended to choose the robot waist as its
root body. The ``base_link`` can be attached to the root in any
arbitrary position or orientation; for every hardware platform there
will be a different place on the base that provides an obvious point
of reference. Note that REP 103 [1] specifies a preferred orientation
for frames.

base_footprint
''''''''''''''

The coordinate frame called ``base_footprint`` projects the
``base_link`` position on the floor.

left_wrist and right_wrist
''''''''''''''''''''''''''

The coordinate frame called ``left_wrist`` defines the position and
orientation of the left arm regardless of the tool (grasping device
for instance) attached to it.

The coordinate frame called ``right_wrist`` defines the equivalent
frame for the right arm.


left_hand and right_hand
''''''''''''''''''''''''

The coordinate frame called ``left_hand`` defines the position and
orientation of the left arm end effector.

If the end effector is a grasping device, the frame should be located
at the recommended object grasping location. The frame orientation is
defined as X the axis which should be collinear with the object axis
during the grasping process, Y the axis going "toward" the reached
object and Z the axis orthogonal to the (X,Y) plan.


The coordinate frame called ``right_wrist`` defines the equivalent
frame for the right arm.


left_ankle and right_ankle
''''''''''''''''''''''''''

The coordinate frame called ``left_ankle`` defines the position and
orientation of the left leg regardless of the support body geometry.


The coordinate frame called ``right_ankle`` defines the equivalent
frame for the right leg.


left_sole and right_sole
''''''''''''''''''''''''

The coordinate frame called ``left_sole`` defines the position and
orientation of the left leg support body. The (X,Y) plan of this frame
must be coplanar with the support body contact surface. It is
recommended to choose the origin as the projection of the body center
on the contact surface.


The coordinate frame called ``right_sole`` defines the equivalent
frame for the right leg.


left_toe and right_toe
''''''''''''''''''''''

The coordinate frame called ``left_toe`` defines the position and
orientation of the left leg toe body. The (X,Y) plan of this frame
must be coplanar with the toe body contact surface. It is recommended
to choose the origin as the projection of the body center on the
contact surface.


The coordinate frame called ``right_toe`` defines the equivalent frame
for the right leg.


gaze
''''

The coordinate frame called ``gaze`` defines the head position and
orientation regardless of any sensors (camera for instance).


chest
'''''

The coordinate frame called ``chest`` is attached to the lowest body
of the model which is a parent of ``left_hand``, ``right_hand`` and
``gaze``.


map and odom
''''''''''''

See REP 105 [1] for ``map`` and ``odom`` frames definition.


Frame Hierarchy
---------------

``base_link`` <-- ``chest`` <-- ``gaze``
``base_link`` <-- ``chest`` <-- ``left_wrist`` <-- ``left_hand``
``base_link`` <-- ``chest`` <-- ``right_wrist`` <-- ``right_hand``
``base_link`` <-- ``left_ankle`` <-- ``left_sole`` <-- ``left_toe``
``base_link`` <-- ``right_ankle`` <-- ``right_sole`` <-- ``right_toe``

Frame Authorities
-----------------

Unlike mobile bases, the transformation from ``base_link`` to
``base_footprint`` is not rigid on humanoid robots and is broadcasted by
an external node.


Exceptions
----------

The scope of potential robotics software is too broad to require all
ROS software to follow the guidelines of this REP.  However, choosing
different conventions should be well justified and well documented.


Compliance
==========

This REP depends on and is compliant with REP 103 [1] and REP 105 [2].


References
==========

.. [1] REP 103, Standard Units of Measure and Coordinate Conventions
   (http://www.ros.org/reps/rep-0103.html)

.. [2] REP 105, Coordinate Frames for Mobile Platforms
   (http://www.ros.org/reps/rep-0105.html)

Copyright
=========

This document has been placed in the public domain.