Error: package 'rqt_plot' not found
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I am studying this page: http://wiki.ros.org/ROS/Tutorials/Und... in: Melodic Ubuntu 18.04
My questions: When: $ rosrun rqt_plot rqt_plot
I saw: [rospack] Error: package 'rqt_plot' not found
Why? How to slove it?
Note: I checked in /opt/ros/melodic/share, there are rqt_graph,rqt_gui,rqt_gui_py,nothing about rqt_plot.
Thank you for your kindness and your next answers.