WEBVTT

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What is a ros2 launch file?

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Let's start with the problem.

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So let's take the camera driver node we used to explain ros2 parameters.

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You start this node for one camera with three parameters the USB device name, the FPS, and a simulation

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mode flag.

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Note that you can also rename the node here.

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Now you want to add another camera driver node for another camera on your robot.

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You start a new camera driver node in another terminal, and of course you rename the node and set all

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parameters values.

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You could also use a YAML file here if you want.

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Oh, and there is a third camera on your robot.

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So that's another node that you start in another terminal.

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And that's not all.

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Let's say you want to add a robot new station node with one parameter.

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This time your application is still not complete.

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You add two LED panel nodes with more remappings and one parameter each, and add etc. etc. you continue

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to add nodes to run your application, each node in its own terminal, with all the options required

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to name the node, set the parameters, etc. as you can see, that's becoming a real mess and it will

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take you forever to launch that every time.

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Plus, with all that configuration, you may make some mistakes that will be long to debug.

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So at this point you might want to run a script to start everything automatically and not manually.

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That way you can truly scale your application.

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Well, that's exactly what a launch file does.

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Here I have put all the nodes and configuration inside the launch file.

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A launch file will allow you to start everything from one single file.

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You can start your nodes, apply some remapping, set some parameters, and even load YAML files.

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That way you will be able to quickly launch your application and to create different launch files for

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different startup modes of your robot.

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In a real application, it's not uncommon for a robot to have something like ten nodes and maybe 200

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or more parameters.

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Without using launch files, it will be impossible to start the robot application.