WEBVTT 00:00.290 --> 00:07.370 If you followed me in the last laboratory lesson where we visualize the Erdf model of the robot in Arvis 00:07.370 --> 00:15.080 and if like me, you are a lazy person, you are probably wondering, isn't there a better and faster 00:15.080 --> 00:21.860 way to visualize a model in RVs without the need of opening all those terminals and execute all those 00:21.860 --> 00:22.610 commands? 00:23.200 --> 00:28.810 Fortunately, the answer is yes and is called launch files in Ros two. 00:29.990 --> 00:37.700 Lunch files is a tool available in Ros2 that allows you to create a list of functionalities and to start 00:37.700 --> 00:39.680 all of them with a single command. 00:40.480 --> 00:47.110 As we have noticed at this point of the course to start different functionalities of our application, 00:47.110 --> 00:51.160 we need to execute several commands in separate terminals. 00:51.430 --> 00:58.750 For example, we had to start a terminal to run the robot estate publisher node, which reads the Urdf 00:58.750 --> 01:03.580 model of the robot and publish it within our ros2 topic. 01:04.260 --> 01:12.120 Then we also had to start the joint state publisher note to move the robots joint and also the RVs to 01:12.120 --> 01:17.460 Node to visualize all of these components in the RVs graphical interface. 01:18.380 --> 01:20.210 For more complex application. 01:20.210 --> 01:27.350 It may also be needed to open additional terminals to configure parameters or to view their content. 01:28.010 --> 01:34.670 Obviously, as the complexity of our robotic application increases the number of nodes to start and 01:34.670 --> 01:40.790 the number of parameters to configure or to change during the execution of the application also increases 01:40.790 --> 01:41.840 exponentially. 01:42.170 --> 01:48.320 As a result, the number of operations and the number of terminals that we need to open to configure 01:48.320 --> 01:51.470 a start, all of those nodes also increases. 01:52.520 --> 02:00.590 To facilitate these management roles provides launch files which are files that can be written in Python, 02:00.710 --> 02:04.520 XML or Yaml and contain a list of operations. 02:04.520 --> 02:11.420 So a set of instructions, a list of instructions to be executed in order to start a certain application 02:11.420 --> 02:13.250 or a certain functionality. 02:14.110 --> 02:18.210 Through a simple command, the Ros two Launch command. 02:18.220 --> 02:22.960 It is possible to automatically execute a list of operations. 02:23.790 --> 02:30.330 For example, you can list a series of nodes to start and it is also possible to declare dependencies 02:30.330 --> 02:31.110 between them. 02:31.350 --> 02:39.180 For example, starting one node before another one or even waiting for one to finish its execution before 02:39.180 --> 02:41.160 starting another and so on. 02:41.460 --> 02:47.910 It is also possible to configure multiple parameters for different nodes at the same time so that they 02:47.910 --> 02:52.170 are correctly configured according to our needs when they start. 02:52.820 --> 02:59.660 Furthermore, it is also possible to start application and processes that are also external to Ros two 02:59.660 --> 03:03.890 and can start other functionalities to interact with the robot. 03:04.850 --> 03:08.930 These components are the building blocks of a launch file. 03:08.930 --> 03:15.260 And so they describe its functionality and indicate the list of operations that the launch file will 03:15.260 --> 03:16.730 start and manage. 03:17.540 --> 03:23.840 Since a single large file can contain an arbitrarily large list of instructions to start, one might 03:23.840 --> 03:30.110 be thinking of listing all the instructions and therefore starting all the nodes of the robot's functionalities 03:30.140 --> 03:31.910 inside a single launch file. 03:32.650 --> 03:39.490 This approach violates one of the fundamental principles of the launch file, which is composition and 03:39.490 --> 03:40.540 reusability. 03:41.080 --> 03:47.140 A launch file should contain a list of operations that have a logical and functional relationship with 03:47.140 --> 03:47.920 each other. 03:48.130 --> 03:54.760 This way different launch files can be created one for each application and functionality of the robot. 03:55.540 --> 04:02.380 All of these lounge files can then be stacked together by another launch file that is responsible for 04:02.380 --> 04:04.700 starting all the robots functionalities. 04:04.720 --> 04:09.070 Considering the dependencies and the priorities of each functionality. 04:10.110 --> 04:15.990 Throughout the course, we are going to use Python for creating lunch files, which is the default approach 04:15.990 --> 04:23.820 used in Ros two, although XML or Yaml can also be used since they are not really programming languages, 04:23.850 --> 04:30.990 they offer limited functionalities and cannot be used to create advanced and complex robotics application. 04:32.340 --> 04:40.470 Creating a file in Ros2 is related to creating a list of operations that needs to be executed in order 04:40.470 --> 04:42.630 to start a certain application. 04:42.630 --> 04:47.040 So this list is contained within a launch description. 04:48.100 --> 04:54.700 Primarily to add this list and to start any application program or process or instruction. 04:54.700 --> 04:59.170 We will use two libraries that are launch and launch. 04:59.170 --> 04:59.950 Ross. 05:00.860 --> 05:05.870 Since these two libraries contain many modules and many functionalities. 05:05.960 --> 05:13.070 As a general guideline, you can think of the launch library as containing the functionalities for managing 05:13.070 --> 05:19.790 and configuring the launch file itself and its interface with the outside world, such as, for example, 05:19.790 --> 05:27.350 the interface offered to the user or also to other launch files that are using it, as well as its interface 05:27.350 --> 05:30.170 with the operating system and other applications. 05:30.650 --> 05:38.060 Instead, the launch underscore Ross Library contains functionalities that are specific to Ross two, 05:38.270 --> 05:42.080 such as managing Ross two nodes and parameters. 05:43.040 --> 05:48.890 In the next laboratory lesson, we will see how to use this tool to reproduce all the steps required 05:48.920 --> 05:51.680 to visualize the Erdf model of the robot in. 05:52.280 --> 05:56.690 But this time using only one terminal and only one command.