When run rbx1_nav, and rviz :fixed frame :fixed frame [map] do not exist

edit

Hi,everyone. I install ros-by-exanple-indigo code on my computer.And I prepare to test fake robot simulator.However,Once I run the .launch file there will be a mistake in rviz.See follow.

run command:

roscore

and

roslaunch rbx1_bringup fake_turtlebot.launch

Then:

rosrun rviz rviz -d 'rospack find rbx1_nav' /sim.rviz

then there's a mistake in rviz,

Global Status ：error fixed frame :fixed frame [map] do not exist

(the node works fine, as I publish the command to it and it can show it moves from the command line screen. So there should be some problems with the rviz I guess.)

What direction should I go?

Thanks.