[ros-users] frame_id naming convention

ROS Community,

After some recent troubleshooting with old code, I noticed that stageros changed the laser's frame_id to base_laser_link from base_laser, presumably to match the PR2's frame_id convention. Is anyone aware of documentation explaining the rationalle for the "*_link" frame_id naming convention? base_link made sense to me since it is something like a convenient virtual frame that links together more physical frames like base_laser and base_footprint. However, base_laser_link doesn't match my (possibly flawed) concept of a "link" frame.

Also, I noticed that, at least for the PR2 simulator, the PR2's tf tree is very shallow with base_footprint being the parent frame to a large number of frames. I would have thought that tf tree would closely mimic the physical degree of freedom heirarchy in the PR2 (i.e. base->torso->upper_arm->lower_arm, etc.) Is there a reason for the PR2s shallow tf tree?

Thanks,

Mike Boulet