This is a known issue in the robot state publisher / urdf I'm working on right now. The next release of the robot_model stack will include a fix. Until then the workaround you describe is your best way to deal with this problem. Wim On Tue, Jun 22, 2010 at 10:05 AM, Morgan Quigley wrote: > Hi Grace, > > I came across something similar last week. In my case, adding a third > link "fixed it," (i.e, 2 joints, 3 links), since an error check inside > the state publisher was failing if there were only two resulting > transforms. > > -Morgan > > > > On Tue, Jun 22, 2010 at 9:54 AM,   wrote: >> Hi everyone, >> >> My name is Grace Lee and I am an undergraduate research assistant at USC's >> Interaction Lab. I am currently writing a urdf for a human model that will >> be interacting with PR2 in the gazebo. When I run the command "roslaunch" on >> my launch file, I get this error: [ERROR] 1277225053.038870000: Could not >> compute link poses. The tree or the state is invalid. >> >> I have parsed the urdf and the tree structure seems correct - i.e. $ rosrun >> urdf check_urdf [my_urdf_name].xml shows that there is one child (which is >> correct btw). The urdf and the state_publisher.cpp seems to be correct as >> well. Any insights into the source of this problem would be greatly >> appreciated. >> >> Sincerely, >> >> Grace Lee >> _______________________________________________ >> 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 > -- -- Wim Meeussen Willow Garage Inc.