RLException: [XXX] is neither a launch file in package [XXX] nor is [XXX] a launch file name报错信息解决方法

在运行roslaunch时出现了类似下面的错误：

RLException: [mav_hovering_example.launch] is neither a launch file in package [rotors_gazebo] nor is [rotors_gazebo] a launch file name
The traceback for the exception was written to the log file

这是因为setup.bash文件没有进一步说明包的来源，解决方法是：

source catkin_ws/devel/setup.bash