[ros-users] frame_id naming convention

Tully Foote tfoote at willowgarage.com
Sat May 15 01:52:32 UTC 2010

  To your original question.  We use the name *_link in the robot because
they are auto generated from the physical links in the URDF.  On the PR2 the
base_laser_link is attached to the base_link by a fixed joint, whereas the
laser_tilt_link goes through the spine and the tilting joint.  The
base_footprint is an example of a convenience frame, where it is the
position of the base, but oriented vertically even if the robot rocks on its


On Fri, May 14, 2010 at 5:00 PM, John Hsu <johnhsu at willowgarage.com> wrote:

> Hi,
> As far as I know, PR2's tf tree is designed for transforms efficiency and
> not meant to represent the PR2 kinematics structures.  Also, tf is exactly
> the same whether you're running in simulation or on the robot.
> There are various ways to see the PR2 kinematics tree structure, for
> example you can use tools in urdf package:
> rosmake urdf
> rosrun xacro xacro.py `rospack find pr2_description`/robots/pr2.urdf.xacro
> > /tmp/pr2.urdf
> rosrun urdf urdf_to_graphviz /tmp/pr2.urdf
> evince pr2.pdf
> Regards,
> John
> On Fri, May 14, 2010 at 4:39 PM, Wim Meeussen <meeussen at willowgarage.com>wrote:
>> > Wim, I'm not sure I understand this rationale.  Somewhere someone is
>> > chaining all the transforms and computing the shallow tree.
>> The shallow tree is only computed once, and then published over tf. So
>> every tf listener can efficiently compute transformations between
>> links. If we publish the more natural tree, then every single tf
>> listener would have to do extra computations to chain links together.
>> > Why not just
>> > publish a more "natural" tree, along with the pre-computed transforms
>> that
>> > go into the shallow tree?
>> I'm not sure I understand what you mean. Tf doesn't allow us to
>> publish the same tree twice.
>> Wim
>> --
>> --
>> Wim Meeussen
>> Willow Garage Inc.
>> <http://www.willowgarage.com)
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Tully Foote
Systems Engineer
Willow Garage, Inc.
tfoote at willowgarage.com
(650) 475-2827
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