How to get the arguments or parameters of launch file in node file?

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Hello, I'm using ROS melodic of Ubuntu 18.04.

I'm trying to spawn 4 different robots and get their pose every time in the Gazebo simulation.

I had gotten /odom topic of each, but also noticed /odom topic is the relative from a local frame.

So I additionally need to get each robot's initial pose to convert from the local /odom to global /odom.

However, I practically set the initial pose in launch file, not Python node file.

If I can get those arguments or parameters (actually I'm not still familiar with the launch file so I'm not sure my word is right) in the Python node file, I think I can do many things wrt pose correction.

More specifically, I want to get arguments like

<arg name="init_pose" .......>

in the Python file.

So if anyone who is familiar with the launch file is here, would you please give me some advice?

Thanks in advance :)