Run the demo Explore the Gazebo world. Check the tf tree via rqttftree and obtain the output as below:

rqttftree output

You can see that the tf of basefootprint -> baselink is published by the node robotstatepublisher.

But "tfmonitor" shows "unknownpublisher" for basefootprint -> baselink.

RESULTS: for base_footprint to base_link
Chain is: base_link -> base_footprint
Net delay     avg = 1114.58: max = 1164.52

Frames:
Frame: base_footprint published by unknown_publisher Average Delay: 0.00476341 Max Delay: 0.02

All Broadcasters:
Node: unknown_publisher 124.051 Hz, Average Delay: 0.00459184 Max Delay: 0.02

Also in the tf tree drawn by "rosrun tf viewframes", there is no tf from basefootprint to base_link.

tf view_frames output

Also notice that compared with the rqttftree output, there are many other tfs missing in the view_frames output.

Is this a bug in tfmonitor and viewframes? Or some configurations in the demo are incorrect?