why use xacro to generate a single file?

[sancelot]

My question may be silly,

but I do not understand why use a macro to generate a single file ????

[gavanderhoorn]

Not a silly question at all.

If you are referring to the use of xacro in the load_...launch files: ROS-Industrial robot support packages are all structured in a similar way.

All robot support packages contain -- per robot variant -- a top-level .xacro file which does nothing more than instantiate the model using its xacro:macro, and a file defining that xacro:macro (in the ..._macro.xacro file).

If we only ship .xacros, we have to use xacro to convert it to plain URDF so it can be loaded into the robot_description parameter.

And the reason we only ship .xacros is because we want these robot support packages to be as useful as possible. If we'd only provide .urdfs, the models could not be used to compose more complex scenes (with multiple robots fi). Because .xacros can be converted to .urdfs, shipping those covers all main use-cases.

So even if, in the end, the top-level .xacros convert to a single file with only a single robot model in them, that's just to make it easy to use them stand-alone (ie: when you don't want to create a composite file).

By using a slightly more complex setup, we cover both use-cases and it keeps everything following the same conventions, structure and layout.

[gavanderhoorn]

Closing due to inactivity.