WEBVTT 00:00.080 --> 00:06.650 In this lesson, you will see how to create your first custom Ros2 interface and we will create a message 00:06.650 --> 00:07.010 here. 00:07.010 --> 00:10.340 But first of all, where will you write your interfaces? 00:10.340 --> 00:12.590 Where will you write the message definition? 00:12.590 --> 00:18.680 If we go to our rust workspace in the source folder, we already have two packages. 00:18.680 --> 00:19.970 So in which package? 00:19.970 --> 00:26.210 Well, basically you could technically add message definitions in any package you want. 00:26.240 --> 00:31.910 However, it will be much easier for you to create all the custom interfaces that you have in a single 00:31.910 --> 00:39.200 package dedicated only to custom interfaces that will prevent you from having a dependency mess in the 00:39.200 --> 00:44.060 future, and when you need to import a custom interface in another package, for example, from the 00:44.060 --> 00:48.890 Python package here, you just need to add a dependency to that new interface package. 00:48.890 --> 00:49.700 And that's it. 00:49.700 --> 00:51.740 So let's create a package. 00:51.740 --> 00:54.380 And that's something we will need to do only once okay. 00:54.380 --> 00:59.540 Because once we have this package, any new interface we add is going to be in that same package. 00:59.540 --> 01:02.530 So we go to our source folder okay. 01:02.560 --> 01:04.360 Where we have already our two. 01:04.390 --> 01:05.860 Existing packages. 01:05.860 --> 01:11.110 And we are going to do Ros2 pkg create and I'm going to name it. 01:11.140 --> 01:14.650 My robot interfaces. 01:14.650 --> 01:19.090 So for the name I recommend that you start with the name of your application. 01:19.090 --> 01:21.910 So if your robot here I'm just using my robot. 01:21.940 --> 01:25.630 If your robot is named ABC, you're going to put ABC. 01:25.720 --> 01:30.940 Or if you have an application name, you just put the application name and then underscore interfaces 01:30.970 --> 01:31.150 okay. 01:31.180 --> 01:36.580 We're going to use interfaces as a suffix here to make it clear that this is an interface package. 01:36.580 --> 01:38.770 And then well then that's it. 01:38.770 --> 01:44.650 You could actually put a build type with amount CMake. 01:44.650 --> 01:49.390 But actually if you don't provide it, it's just going to be a CMake by default. 01:49.390 --> 01:51.040 And we don't really need it anyway. 01:51.040 --> 01:53.020 And we're not going to provide any dependencies. 01:53.020 --> 01:59.950 So what I do to create an interface package, I just do Ros to create and the name of the package. 02:00.040 --> 02:01.480 Let's press enter. 02:01.480 --> 02:06.580 And you see we have some logs for the files that were created. 02:06.610 --> 02:09.250 A warning for the license that we can just ignore. 02:09.250 --> 02:12.610 And now we have our new package here. 02:12.610 --> 02:19.510 And if I go inside my robot interfaces, you see this is a C plus plus package. 02:19.510 --> 02:22.360 So we will need the package dot XML file. 02:22.360 --> 02:27.400 As for any package in Ros2, we will also need Cmakelists.txt. 02:27.430 --> 02:30.850 That's where we're going to provide rules to build our interfaces. 02:30.850 --> 02:34.030 But then we don't need src and we don't need include. 02:34.030 --> 02:36.040 So what I'm going to do is just I'm going to clean that. 02:36.040 --> 02:40.090 I'm going to remove the include and I'm going to remove the SRC. 02:40.480 --> 02:40.720 Okay. 02:40.750 --> 02:46.360 So now we just have those two files and we will need to add a few lines inside those files here so we 02:46.360 --> 02:48.400 can build our interfaces. 02:48.400 --> 02:50.440 So let's open. 02:50.620 --> 02:56.350 I'm going to open here this workspace with Visual Studio Code. 02:57.810 --> 03:02.100 and let's go to my robot interfaces. 03:02.280 --> 03:04.410 For example in package dot XML. 03:04.410 --> 03:07.830 So you see here build tool depend its element CMake. 03:07.860 --> 03:08.760 That's what we want. 03:08.790 --> 03:10.680 And we have the build type here as well. 03:10.710 --> 03:12.510 Now what do we add here. 03:12.540 --> 03:15.930 Well there are three lines you need to add in package dot XML. 03:15.930 --> 03:21.600 And in order not to make mistakes, it's actually better to just copy and paste them from an existing 03:21.690 --> 03:22.710 configuration. 03:22.710 --> 03:24.660 So we can go on. 03:24.750 --> 03:29.700 Let's go on the internet and you can just type custom Ros2 interfaces. 03:29.700 --> 03:34.770 We're going to find something and let's go for example to that website. 03:34.770 --> 03:37.650 I might link it to this lesson. 03:38.250 --> 03:41.550 And this website is actually pretty nice for Ros2 tutorials. 03:41.550 --> 03:42.480 Robotics back end. 03:42.480 --> 03:45.780 And I'm absolutely not saying that just because it's my own website. 03:45.810 --> 03:50.910 Okay, so in this tutorial, well, we don't really want to read the tutorial. 03:50.910 --> 03:53.010 We just want to go down here. 03:53.010 --> 03:57.920 You can find the same information under Also ros2 official documentation. 03:57.920 --> 03:59.720 You will find those same lines here. 03:59.720 --> 04:06.080 But you see, when we set up a package for Ros2 custom interfaces, we have three lines we need to add. 04:06.110 --> 04:06.470 Okay. 04:06.500 --> 04:07.790 Build tool depend. 04:07.820 --> 04:09.080 I'm going to zoom in a bit. 04:09.110 --> 04:14.870 Build tool depend with Ros ideal default generators and then execute depend with Ros. 04:14.900 --> 04:18.770 Ideal default runtime and member of group Ros. 04:18.800 --> 04:20.450 Ideal interface packages. 04:20.450 --> 04:25.700 So that's why I'm not just going to write them in order not to make mistakes, I'm just going to copy 04:25.700 --> 04:27.470 and paste them. 04:27.530 --> 04:28.280 Okay. 04:28.310 --> 04:34.340 After the build tool here after build tool depend I just add those three lines. 04:34.370 --> 04:34.520 Okay. 04:34.550 --> 04:40.820 There is nothing really to understand Ros ideal is basically the functionality that's going to create 04:40.820 --> 04:42.260 and manage interfaces. 04:42.260 --> 04:44.300 So you just need to add those lines. 04:44.300 --> 04:49.670 The good thing is after you do this once that's basically it for your whole application. 04:49.700 --> 04:50.120 All right. 04:50.120 --> 04:51.770 So that's it for package dot XML. 04:51.770 --> 04:59.050 We can close it and then we can open Cmakelists.txt and we will first clean a bit. 04:59.050 --> 05:05.260 I don't need this build testing stuff and just remove those comments here. 05:05.290 --> 05:12.220 Okay, so we have the minimum thing for the list.txt and I'm going to go back to that web page. 05:12.520 --> 05:14.350 You need to add this. 05:14.380 --> 05:19.240 Okay Findpackage with Ross ideal default generators. 05:19.240 --> 05:23.080 Then we are going to add Ross ideal generate interfaces. 05:23.080 --> 05:28.060 That's the command to generate interfaces where we're going to put the path to all of the interfaces 05:28.060 --> 05:28.690 we create. 05:28.690 --> 05:34.360 And then you have amend export dependencies with Ross ideal default runtime. 05:34.360 --> 05:37.570 So again it's not really important to understand anything here. 05:37.600 --> 05:40.150 Just have to add this to your configuration. 05:40.150 --> 05:45.550 So let's go here after Findpackage here and before element package. 05:45.850 --> 05:47.200 Let's add a line. 05:47.350 --> 05:49.570 Let's add a space here. 05:51.580 --> 05:52.150 Okay. 05:52.180 --> 05:54.670 And you see your custom interfaces will be here. 05:54.700 --> 05:59.890 One per line and no comma for separating lines, as you can see. 05:59.920 --> 06:04.990 So I'm just going to remove everything now and let's save that. 06:04.990 --> 06:07.180 And now the package is configured. 06:07.210 --> 06:07.570 Okay. 06:07.600 --> 06:10.330 So we have three lines in the package dot XML. 06:10.330 --> 06:16.930 And then we have this fine package this function here and this element export dependencies here for 06:16.930 --> 06:18.400 the Cmakelists.txt. 06:18.430 --> 06:23.470 Now that we have set up the package we can create our first interface. 06:23.470 --> 06:24.910 So how to do that. 06:24.940 --> 06:31.750 Well I'm going to go back here in my robot interfaces package. 06:31.750 --> 06:37.750 And to create a message we are going to create first an MSG folder. 06:38.200 --> 06:38.590 Okay. 06:38.620 --> 06:41.770 And that's where we are going to put all our messages. 06:41.800 --> 06:46.030 I go inside the MSG and let's create a new interface. 06:46.030 --> 06:49.720 Let's say we want to publish the hardware status of our robot. 06:49.720 --> 06:53.010 So that's going to contain a few information about the robot. 06:53.040 --> 06:56.340 For example, I don't know the name, the version number, the temperature. 06:56.520 --> 06:57.810 All kinds of stuff. 06:57.810 --> 06:59.490 So let's create an interface. 06:59.490 --> 07:04.980 Touch hardware status dot msg. 07:05.040 --> 07:09.750 So what are the rules to create names for interfaces? 07:09.750 --> 07:14.760 Well you are going to start with an uppercase and you're going to use upper camel case okay. 07:14.790 --> 07:18.300 So no dashes no underscore is very important. 07:18.300 --> 07:22.650 And you're going to separate each word by an uppercase. 07:22.650 --> 07:27.870 That is going to have an importance for example for the C plus plus header files as we will see later. 07:27.870 --> 07:29.190 So you start with an uppercase. 07:29.190 --> 07:31.110 Each new word has an uppercase. 07:31.140 --> 07:33.840 Also don't write message okay. 07:33.840 --> 07:36.840 We could say hardware status message or something. 07:36.840 --> 07:37.500 Don't write this. 07:37.530 --> 07:38.850 It's going to be redundant. 07:38.850 --> 07:41.070 So just the name of the interface. 07:41.070 --> 07:45.630 And then dot msg for a message definition. 07:45.630 --> 07:52.340 Now I'm going to go back here and let's edit that file so we can use primitive data types. 07:52.340 --> 07:57.680 We can also use existing messages from that package or from other packages. 07:57.680 --> 07:59.240 Let's keep things simple here. 07:59.240 --> 08:01.370 And let's just use primitive types. 08:01.370 --> 08:06.560 Let's say we have a float 64. 08:06.590 --> 08:09.980 That's going to be the temperature okay. 08:09.980 --> 08:12.740 I'm just going to use a few examples with some types. 08:12.740 --> 08:18.590 And then let's say bool are mortals ready. 08:18.740 --> 08:19.400 Okay. 08:19.460 --> 08:24.980 And let's add a string debug message okay. 08:25.010 --> 08:30.590 So you can see I write one field on each line okay. 08:30.620 --> 08:34.070 There is no other separation, no comma, no punctuation. 08:34.100 --> 08:36.710 The first thing I do is I put the type. 08:36.710 --> 08:38.930 So here those are primitive types. 08:38.930 --> 08:40.100 And then the name. 08:40.100 --> 08:43.340 And to separate words I use underscore okay. 08:43.370 --> 08:47.120 It's very important here to use underscores and nothing else. 08:47.120 --> 08:47.930 And that's it. 08:47.930 --> 08:49.420 So it's not really complicated. 08:49.450 --> 08:51.280 Now I'm going to save. 08:51.310 --> 08:56.260 Just make sure that you use exactly the the syntax or the good syntax for primitive types. 08:56.260 --> 08:57.430 I'm going to save this file. 08:57.430 --> 08:58.720 Make sure you save everything. 08:58.720 --> 09:06.190 And then well once I have created a new interface, all I need to do is to go back to my cmakelists.txt. 09:06.400 --> 09:10.270 And inside this rose ideal generate interfaces. 09:10.270 --> 09:16.750 I'm going to add a new line with double quotes, and I'm going to put the path to the interface. 09:16.750 --> 09:26.290 So from here we need to go to the msg folder slash hardware status dot m s g. 09:26.470 --> 09:27.880 And that's it okay. 09:27.910 --> 09:35.500 So you see after you've set up the package, adding a new interface is just about creating a file in 09:35.500 --> 09:40.990 this folder and then adding the path to the file here in that function. 09:40.990 --> 09:44.740 Then you save and then let's go back to the terminal. 09:44.740 --> 09:53.410 Let's stay in that one and let's go back to our Ros2 workspace folder here, and let's do a call on 09:53.410 --> 09:54.040 build. 09:55.060 --> 10:00.250 I'm going to also use packages select to only build this interface. 10:00.250 --> 10:07.450 So my robot interfaces let's build it might take a bit of time the first time that you build some interfaces. 10:10.150 --> 10:11.740 Okay so it took 11 seconds. 10:11.740 --> 10:12.700 It's not that bad. 10:12.700 --> 10:16.210 And now the interface has been built okay. 10:16.240 --> 10:23.410 If you go to the install folder inside the My Robot interfaces, you could find and check the C plus 10:23.410 --> 10:24.910 plus and the Python files. 10:24.940 --> 10:25.120 Okay. 10:25.150 --> 10:27.250 You can try to do that on your own if you want. 10:27.280 --> 10:31.480 But once again it's not really that important because they exist and we don't need to check them. 10:31.480 --> 10:32.890 We can just use them. 10:32.890 --> 10:38.050 And let's see in this terminal the interface we have just created. 10:38.050 --> 10:44.350 So because we have just built here in that terminal, if we're using another one that we haven't sourced 10:44.380 --> 10:46.560 after that we need to source it now. 10:46.560 --> 10:51.090 So let's source the bash RC so we can source our workspace. 10:51.120 --> 10:55.230 And then I can do Ros2 interface show. 10:55.230 --> 10:59.490 And let's start with the package name my robot and let's press tab. 10:59.490 --> 11:01.200 You see I have only one. 11:01.200 --> 11:08.880 So my robot interfaces slash msg slash hardware status I press enter. 11:08.880 --> 11:12.990 And this is the message definition that I have okay. 11:13.020 --> 11:14.790 So now you understand this. 11:14.790 --> 11:17.070 We have done several times Ros2 interface show. 11:17.070 --> 11:23.610 But now you see the whole process to create an interface to build it and then to see it on the terminal. 11:23.640 --> 11:24.120 Great. 11:24.120 --> 11:27.900 And make sure that you can see the interface with this command. 11:27.930 --> 11:28.080 Okay. 11:28.110 --> 11:33.120 If you cannot see the interface, then you will not be able to use the message in your code in the next 11:33.120 --> 11:33.690 lesson. 11:33.690 --> 11:35.880 So make sure that you can do that if needed. 11:35.880 --> 11:41.370 You remove the package, you clean everything up and you start everything again from scratch because 11:41.370 --> 11:42.540 there are quite a few steps here. 11:42.540 --> 11:45.540 So make sure that this is working before you go to the following.