ros::NodeHandle param

[hopechen8810]

@kwc
I write a ros node(a imu ros node) in c++ like below to set a param named port and set the default to "/dev/ttyAMA2". in the launch file, load a yaml file and set the port param to "/dev/ttyS0" which is the serial device on my develop board.

then I use service in ubuntu to start the program automatically, howerver the ros node will set the port param to /dev/ttyAMA2". why?