Parameters and Arguments at Startup

Launch files can carry node configuration that would otherwise need to be typed separately every time.

The pinned launch tutorial distinguishes executable arguments from ROS-specific arguments/configuration.

Parameters in a launch Node

If a node declares a parameter, a Python launch action can pass a value with a parameters list.

Example shape:

Node(
    package='some_package',
    executable='some_node',
    parameters=[{'example_parameter': 42}],
)

For the required course path, you may apply this to a parameter you added as an optional Unit 7 stretch goal or use Turtlesim in a separate practice launch.

Remaps versus parameters

Do not mix them conceptually:

remapping → changes graph names
parameter → changes node configuration values
argument → passed to executable/launch behavior

Inspect the result

After launching a parameterized node, use:

ros2 param list
ros2 param get <node_name> <parameter_name>

The launch file is not proof by itself. The running node's parameter state is stronger evidence.

Checkpoint

Give one example of something you would configure with a remap and one with a parameter. Explain the difference.