WEBVTT

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Now that you understand the purpose of launch files, let's see how to actually create one for your

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Ros2 application.

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And the first question is where do we create our launch files.

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So if I go to my workspace in the source folder you see I have three packages.

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So where do I create the launch file.

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Well technically you could add a launch file in any package.

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But as we did for our interfaces, we are going to create a dedicated package for the launch files.

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We will add all the launch files for our application and also configuration files for example the YAML

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files.

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This will make it much easier for you to handle dependencies in your application, and also later on

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if you check some other projects.

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If you find other robots for which the code is open source and on GitHub, you will find this organization

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all the time.

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So we're going to create a new package.

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And well let's just first you go to the source folder of your workspace and let's do Ros2 pkg Create.

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And I'm going to start with my robot.

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Okay.

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So if your robot is named ABC, you're going to write ABC.

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Just use the name of your robot or your application.

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And then I'm going to add the bring up suffix.

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Okay.

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So for interfaces we have interfaces for launch file we have bring up.

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This is really common okay.

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You will find this kind of bring up package in a lot of different GitHub projects if you browse online

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for different robots okay.

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So it's always the same thing.

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And I recommend that you use also the name bring up.

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Then what build type do we need to provide?

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Well we can provide payment CMake if we want, but we can also skip it which is going to create anyway,

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even CMake by default.

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And for the dependencies I'm not going to provide any dependency.

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Now we're going to add them as we add more stuff in our launch files.

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So basically just Ros2 pkg PG.

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Create my robot.

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Bring up.

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We have a new package.

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You see some logs?

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The warning for the license.

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Okay.

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And let's go inside.

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So RLS, we have the new package here.

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Let's go inside my robot bring up.

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And what do we have.

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Well, classic stuff with Cmakelists.txt that we will keep package dot XML.

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Very important.

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And then we have include and source.

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We don't need those folders so let's remove them.

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Let's remove include and let's remove source.

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Now I'm going to create a new folder right now called launch okay.

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So now in my package I have this launch folder and those two files.

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And in this launch folder I will write all the launch files for my application.

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Great.

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So now we can open uh let's just open the workspace with VSCode here from the source folder.

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And we can go to our bring up package.

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And what I'm going to do is I'm going to set up the package for installing the launch files.

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Okay?

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Just like when we created the interfaces package, we had a bit of setup here.

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We also have a bit of setup specific for launch files is going to be much quicker.

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First of all, we don't have to do anything in the package dot XML, so you can just keep it like this.

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You see we have build type A1, CMake.

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That's what we want.

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And then we're going to go to the Cmakelists.txt.

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And in that one I'm going to simplify the code here as well.

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I'm going to remove the build testing.

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We don't need that for now.

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And I'm going to remove those comments.

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And now basically the only instruction that we are going to provide here is to say that we want to install

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the launch folder, okay.

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And everything that's inside the launch folder.

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So I'm going to write install and then uppercase Directory.

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Okay.

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Let's go to New Line.

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I'm going to put launch.

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Launch is because that folder is named launch and then destination all uppercase.

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Make sure you don't make any typo.

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And then we are going to write share.

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Okay.

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So we are going to install this inside a share folder.

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Okay.

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That's going to be inside the install folder of your workspace.

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And it's important that you write share here slash.

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And then we're going to put the project name.

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So basically the package name with dollar sign and curly brackets.

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Make sure you don't put parentheses so often.

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This is a common mistake.

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But parentheses now it's curly brackets and project name.

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And you can add a slash here if you want.

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So okay make sure you write exactly this.

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Okay.

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So between find package and payment package you add this install instruction and that's basically it.

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Everything that we will write inside the launch folder here is going to be installed.

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So we only need to write this once.

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That's it.

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Let's make sure we save.

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And while the package is correctly configured.

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So that's basically it.

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You create a Myrobot package.

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Then you create a launch folder and you install this launch folder.

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Now let's create our first launch file.

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For this we are going to add it inside the launch folder.

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So you could go to the terminal.

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I can also just create it here and let's name it number app dot launch dot XML okay so what I'm going

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to start the number of application from this launch file.

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What I want to do is start different nodes.

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So for this example I'm going to start the number publisher and the number counter that we have created

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previously in this course.

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So I'm just going to name this application number app.

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Then you have dot launch and then dot XML because we write an XML file.

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Okay.

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And you can see this is inside the launch folder inside the package.

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So you can do that from the terminal, from VSCode from anywhere you want.

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And then we are going to initialize our launch file.

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And for that it's very easy.

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So we're going to write XML code.

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And we need a launch tag.

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So you open a launch tag like this and you close the launch tag and that's it.

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Your launch file is initialized.

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So for every launch file you create in rust with XML, you need to add those launch tags.

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And everything you write is going to be inside this.

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Then you don't need to provide any indentation okay, it's XML, but still I'm going to add an indentation

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for readability.

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And in this launch file let's say we want to start two nodes I want to start the number publisher node

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and the number counter node.

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To start a node you can provide the node tag just like that.

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So you open it and inside the node tag you have a pkg argument that's going to be the package where

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the node.

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So actually where the executable is.

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And for example let's start the one from my pi pkg.

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And then we have exec okay.

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So we have pkg and exec exec is the executable.

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So number publisher actually you could just check that.

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So here I can do Ros to run package name okay.

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Executable name.

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So to construct a so number publisher to construct a launch file you can just run the commands here

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one by one all the nodes inside terminals.

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And then you can just take the names that you have written here just to make sure that this is correct.

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You see my pi pkg.

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That's the package and number publisher.

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That's the executable.

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And I'm going to close.

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It's just going to be one line for now.

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So I'm going to close like this.

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Okay.

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With a forward slash and a bracket.

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And so what will happen if I launch if I start this launch file.

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Well it's going to start that executable.

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Just like if you would run that node in the terminal.

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Same thing.

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Now let's say that I want to start the number counter.

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And this time let's change.

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Let's use the C plus plus package number counter.

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So you see package executable name.

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So I'm adding another node tag pkg.

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My cp pkg and exec is going to be number counter.

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Okay.

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Just like if you would run that on the terminal.

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Okay.

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And with this simple launch file we have four lines.

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Then we have started two nodes.

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Okay.

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No configuration nothing.

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We're going to add that in the following lessons.

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But you see with just this we start two nodes.

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I'm going to save this.

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And also because you see that from my robot bring up, we are going to execute stuff from two other

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packages.

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So because of that I'm going to go inside my package dot XML of the My Robot Bringer package.

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And after here I'm going to add dependencies.

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Okay.

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So usually I have written the depend tag.

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But for large files you could also use the exec depend tag because well, exec depend is a bit less

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strict than depend.

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And it just means that you need the dependencies for execution.

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Okay.

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Not for compiling, not for building anything, just for execution.

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All right.

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We're not going to compile any code here.

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We just say that we need this package when we execute the launch file.

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So we can use exec depend.

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And my pi pkg okay.

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Here execute depend and then exec depend with my cp pkg exec depend.

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So as a best practice, whenever you see you start to use a new package inside a launch file in this

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package here, then you add the package with exec, depend in the package dot XML file and let's save

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everything.

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Now we can go back to the terminal.

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Let's let's go back to our workspace.

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And let's build on build.

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Let's use packages select to just build my robot.

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Bring up and use the Autocompletion once again okay.

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So this one is always going to be quite quick.

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There is nothing really to compile.

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It's just going to install the the file somewhere in the install folder.

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And now to start it.

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Well to start it is very easy.

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I'm just going to keep this terminal here.

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I'm going to make sure that I source My workspace here with the setup that bash.

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And then well, let's do this to have more space then we can do Ros2 launch.

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Okay.

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So for node you do Ros to run.

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If you want to start a launch file, you do Ros to launch.

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And then you need to provide what the package where the launch file is.

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So that's my robot.

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Bring up my robot.

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Bring up using Autocompletion.

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And if I press tab twice here.

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Well you see I have some options and stuff.

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But you see I have my number app dot launch dot XML.

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So if I just start number app you see I can find it with Autocompletion.

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So Ros2 launch package name and then launch file name.

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Let's start it and you can see what do we have here.

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We have a few logs.

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So stuff where you can find logs here logging verbosity.

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And then you see that for each executable that we start in the launch file, we have a log saying that

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we have started the process.

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It even gives you the PID.

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So the process ID here.

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And you see now we have started an executable named number publisher one.

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Number counter two.

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Okay.

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So that's the executable that has been started.

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And then you see the logs.

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Those are the logs that we directly print from the nodes.

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So we have the number counter node and we have the number publisher node.

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Now well actually I'm going to start some terminals here.

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If I do ros2 node list you see I have my two nodes okay.

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I didn't need to start them from two terminals.

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I just started them from the same launch file.

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Okay.

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If I do ros2 topic list, you see I have my number topic and my number count topic.

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If I do ros2 topic equal number counts just to check that it works.

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And you see I have my data here so it's correctly working I can do RCT graph.

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And well you might refresh.

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You put nodes topics all.

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You also uncheck those boxes here and you will have also that view okay.

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So everything is correctly working.

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Our application has been launched.

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We've just you see this command line and that's how you create an XML launch file.

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So if you want to create a new one you just add a new file here in the launch folder you start with

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a launch tag, and then you add one node tag for each node that you want to start.

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And then that's it.

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You just make sure that you build the package again and that you source the environment.

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And then you can just do Ros2 launch package and launch file name.