Michael, 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 wheels. Tully On Fri, May 14, 2010 at 5:00 PM, John Hsu 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 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. >> > _______________________________________________ >> ros-users mailing list >> ros-users@code.ros.org >> https://code.ros.org/mailman/listinfo/ros-users >> > > > _______________________________________________ > ros-users mailing list > ros-users@code.ros.org > https://code.ros.org/mailman/listinfo/ros-users > > -- Tully Foote Systems Engineer Willow Garage, Inc. tfoote@willowgarage.com (650) 475-2827