WEBVTT 00:00.050 --> 00:05.630 I might have briefly mentioned namespaces a few times during this course, but now is a good time to 00:05.660 --> 00:07.880 explain how to work with them. 00:07.880 --> 00:13.880 This concept doesn't necessarily belong to the launch file section, but as we set them mostly inside 00:13.880 --> 00:18.530 launch files and also with YAML files, I wanted to wait until this point. 00:18.530 --> 00:22.190 So let's start first with the concept of namespaces. 00:22.220 --> 00:24.410 See how to add a namespace to a node. 00:24.410 --> 00:28.070 And finally we will see how to use namespaces in launch files. 00:28.070 --> 00:30.320 So well you can open some terminals. 00:30.320 --> 00:37.490 And when we start a node let's just do a rush to run with my, for example, CBP package. 00:37.490 --> 00:41.000 And let's start the number publisher that we have used quite a lot already. 00:41.030 --> 00:50.090 Well, you know that if I run this and if I do rush to node list, let's also do a rush to topic list. 00:50.930 --> 00:51.320 Okay. 00:51.320 --> 00:54.200 We have this is the node name number publisher. 00:54.200 --> 00:57.770 And we have the number topic published by this one. 00:58.100 --> 01:02.480 Now let's stop And how to add a namespace. 01:02.480 --> 01:04.910 I'm going to add a namespace and show you what it does. 01:05.360 --> 01:11.210 Well, you just do Ross args, just like for everything else, for renaming, for parameters. 01:11.210 --> 01:13.490 And then you add another dash R. 01:13.520 --> 01:13.790 Okay. 01:13.790 --> 01:17.480 So that's going to be considered as a remapping dash R. 01:17.510 --> 01:22.520 And then you have underscore underscore ns for namespace. 01:22.520 --> 01:31.760 So to rename a node you had node like that for namespace you have this and let's say slash test what's 01:31.760 --> 01:32.510 going to happen. 01:32.510 --> 01:34.880 Well first you can see in the logs. 01:35.030 --> 01:40.880 Now we have not just number publisher we have test number publisher okay. 01:40.910 --> 01:44.630 So namespace is going to be added in front of the name. 01:44.630 --> 01:47.630 Well just like you would use a namespace in your code. 01:47.630 --> 01:50.900 If you're already familiar with namespaces you know what it does okay. 01:50.930 --> 01:54.290 It's just adding a name in front of all the other names. 01:54.290 --> 02:00.120 So if I do Ros2 node list now you can see my node is not number publisher. 02:00.150 --> 02:03.240 My node is test number publisher. 02:03.420 --> 02:06.810 And if I do rostopic list you see that. 02:06.810 --> 02:09.000 So we have the result and parameter events. 02:09.000 --> 02:11.250 Those are just kind of on the side. 02:11.250 --> 02:16.830 But you see now my number topic is not number it's test number. 02:16.860 --> 02:17.310 Okay. 02:17.340 --> 02:23.040 So that's one very important thing is that when you add a namespace to a node, when you start, it 02:23.070 --> 02:26.130 is going to change all of the names inside. 02:26.130 --> 02:31.320 So the node name and the topic names, the service name etc.. 02:31.350 --> 02:32.700 Let's check the parameters. 02:32.730 --> 02:35.430 Of course two param list. 02:36.540 --> 02:41.700 Well the parameter name of course doesn't change, but the name of the node has changed. 02:41.700 --> 02:48.390 And so let's come back to the code and I'm going to show you the importance of the leading slash. 02:48.390 --> 02:55.200 So well for example in the Python package it's the same code as the C plus plus one. 02:56.460 --> 03:03.450 You can see that when I created here the name of the node, I didn't put any slash. 03:03.480 --> 03:03.660 Okay. 03:03.690 --> 03:07.080 The same for the topic name. 03:07.080 --> 03:08.850 I didn't add any slash. 03:08.850 --> 03:14.790 And what you can see is if I don't add any slash one leading slash is going to be added. 03:14.820 --> 03:15.150 Okay. 03:15.180 --> 03:16.800 I didn't provide that in the code. 03:16.800 --> 03:23.130 It's been added automatically because you're always going to start from let's call it the root namespace, 03:23.130 --> 03:26.880 which is no namespace, but it's going to add a slash anyway. 03:26.910 --> 03:31.050 So we have slash node name slash topic name. 03:31.050 --> 03:34.830 And here I have added that another test namespace. 03:34.830 --> 03:39.210 So now it's slash test slash number publisher okay. 03:39.240 --> 03:42.300 And by providing the name like this. 03:42.300 --> 03:48.030 So you can see if we don't provide any namespace it's going to add a slash automatically. 03:48.030 --> 03:51.900 But if we provide a namespace it's going to add the namespace in front of the name. 03:51.900 --> 03:57.690 Now let's say for example in this publisher let's say that I add a slash okay. 03:57.720 --> 04:02.320 What's going to happen if I add a slash to this publisher? 04:02.320 --> 04:04.060 So now it's slash number. 04:04.090 --> 04:07.150 Let's save and let's build again. 04:07.510 --> 04:11.680 So I'm going to go to Roster Workspace. 04:11.680 --> 04:14.830 Click on Build packages. 04:14.950 --> 04:19.030 Select with my Pi PG. 04:19.960 --> 04:21.910 Let's just build like this. 04:23.320 --> 04:23.740 What. 04:23.740 --> 04:26.860 We have a warning here but it's not a problem. 04:26.890 --> 04:27.370 Okay. 04:27.370 --> 04:31.150 We haven't done anything bad so let's source. 04:32.620 --> 04:32.950 Okay. 04:32.980 --> 04:33.700 And let's run. 04:33.700 --> 04:34.990 Let's do rush to run. 04:34.990 --> 04:36.520 So let's start. 04:36.550 --> 04:38.470 So I have changed the Python one. 04:38.470 --> 04:45.910 I'm going to of course launch with the Python package with rush to run my Pi PG number publisher. 04:46.480 --> 04:48.520 And then I add a namespace. 04:50.710 --> 04:52.900 So of course it's still working. 04:53.590 --> 05:00.100 And let's do Ros2 node list we have slash test slash number publisher. 05:00.400 --> 05:02.080 If I do roster topic list. 05:03.730 --> 05:07.000 You see we don't have slash test slash number. 05:07.000 --> 05:08.440 We just have slash number. 05:08.440 --> 05:09.460 Why is that? 05:09.460 --> 05:13.960 Because you see in the code I have provided a leading slash. 05:14.080 --> 05:14.440 Okay. 05:14.470 --> 05:20.110 So if you provide a leading slash you're going to say that that's not going to change even if you add 05:20.110 --> 05:21.700 a namespace. 05:21.730 --> 05:22.210 Okay. 05:22.240 --> 05:26.230 You've already said that this is going to be leading slash number. 05:26.230 --> 05:29.590 If you don't provide a slash then a slash is going to be added. 05:29.590 --> 05:33.820 And if you provide a namespace the namespace can also be added. 05:33.820 --> 05:40.960 So if you want to make sure that no namespaces can change topic name a node name or whatever, you add 05:40.990 --> 05:46.450 a slash here at the beginning in your code, but if not, you just don't add any slash. 05:46.450 --> 05:48.400 So that's an important difference here. 05:48.400 --> 05:54.820 And by default here in the code I have not added any slash, which means that I can add as many namespaces 05:54.820 --> 05:58.070 as I want, and it's quite modular this way. 05:58.100 --> 06:04.220 Okay, so let's save again and just again let's build. 06:05.030 --> 06:10.700 I didn't use Simulink install but okay let's source and let's run again. 06:11.900 --> 06:18.650 And now you see it's going to be slash test slash number because I didn't provide a slash. 06:18.650 --> 06:23.210 So that's quite important difference here and something to understand. 06:23.240 --> 06:23.690 All right. 06:23.690 --> 06:29.270 And namespaces are quite useful if you want to split your application for example for different robots 06:29.300 --> 06:31.130 let's say you have three different robots. 06:31.130 --> 06:34.100 And each robot has a node to control the wheel. 06:34.100 --> 06:39.320 And that's basically from the same node using the same topics and services, etc.. 06:39.350 --> 06:44.900 How can you make sure that each robot is not going to get the comments for another robot, and that 06:44.900 --> 06:50.030 you're not going to just mess up communication between your wheel control nodes? 06:50.030 --> 06:56.240 Well, you can just use a namespace like slash robot one for the first, one, slash robot two, slash 06:56.240 --> 06:56.930 robot three. 06:56.930 --> 07:01.430 And then you make sure that the topics for robot one are just for robot one. 07:01.460 --> 07:01.670 Okay. 07:01.700 --> 07:05.630 So all the nodes for the robot one will have a namespace. 07:05.660 --> 07:09.710 All the nodes for the robot two will have another namespace, etc.. 07:09.740 --> 07:10.010 Okay. 07:10.040 --> 07:13.640 So this way you can make your application super dynamic. 07:13.670 --> 07:16.250 You don't even need to change the code at all. 07:16.250 --> 07:20.780 You just add a namespace when you start the node and how to add a namespace. 07:20.780 --> 07:23.870 You do dash r with ns. 07:23.900 --> 07:28.280 So underscore underscore ns and you provide a namespace here. 07:28.280 --> 07:31.340 And now is where I come back to the launch files. 07:31.340 --> 07:35.750 Because usually we're going to start our applications from launch files. 07:35.750 --> 07:39.770 So that's where you are going to add namespaces. 07:39.770 --> 07:42.950 And to add a namespace inside a launch file. 07:42.950 --> 07:43.940 It's very easy. 07:43.970 --> 07:53.600 You see we have our node tag with pkg exec name and namespace namespace. 07:54.830 --> 08:01.680 And we're going to start with a slash and let's say well let's also use test namespace or let's say 08:01.710 --> 08:02.520 ABC. 08:02.730 --> 08:10.980 So let's see what happens if I just add a namespace ABC here for just that node for the number publisher 08:11.010 --> 08:11.970 node only. 08:13.230 --> 08:28.260 So this time I'm going to build the robot bring up and then source and then Rose to launch my robot 08:28.290 --> 08:34.890 bring up with number app dot launch dot XML. 08:36.510 --> 08:41.940 Okay, you can see already the name of the node has changed rose to node list. 08:42.810 --> 08:45.000 So the same thing as we saw previously. 08:45.000 --> 08:48.870 Now it's slash ABC slash my number publisher. 08:48.870 --> 08:57.570 And now if I do rose to topic list you see that the namespace has been applied to the topic. 08:57.570 --> 08:59.310 And here it's kind of weird. 08:59.310 --> 09:01.560 Let's let's see with our cut graph. 09:03.570 --> 09:05.160 And let's understand what's happening. 09:05.160 --> 09:09.240 So if I refresh uh well you can group namespaces here. 09:09.240 --> 09:10.020 You see. 09:10.020 --> 09:15.870 But if I go to zero, maybe it's a bit cleaner here for what we want. 09:15.900 --> 09:22.560 So you see we have our ABC my number publisher node which is publishing to ABC number. 09:22.590 --> 09:25.740 Then we have my number counter which is subscribing to my number. 09:25.740 --> 09:30.210 So of course we have a topic mismatch and those cannot communicate. 09:30.270 --> 09:32.640 But there is one thing that you see. 09:32.670 --> 09:38.340 The topic name here is ABC number in the launch file. 09:38.340 --> 09:40.950 So we have added a namespace ABC. 09:41.130 --> 09:45.330 And then we have say that we want to remap number to my number. 09:45.330 --> 09:49.290 And as you can see that clearly this remapping didn't work. 09:49.290 --> 09:55.090 And that's normal because at this point the topic name is not slash number. 09:55.120 --> 09:59.260 The topic name is slash ABC slash number. 09:59.260 --> 10:03.280 So this remapping is not going to have any effect. 10:03.280 --> 10:04.450 And how to solve this. 10:04.450 --> 10:07.090 Well actually you see I have used the slash here. 10:07.090 --> 10:09.820 So we are just going to remove the slash. 10:09.970 --> 10:12.760 Same thing here in the remap okay. 10:12.790 --> 10:15.190 Because it's going to look for slash number. 10:15.220 --> 10:15.970 Exactly. 10:15.970 --> 10:19.540 If I just put number then it's going to rename number. 10:19.540 --> 10:25.570 Even if it's in slash abt slash number it's going to rename number to my number. 10:25.600 --> 10:34.660 Otherwise I would have needed to do slash ABC slash number to slash ABC slash my number. 10:34.660 --> 10:37.630 But that doesn't make it very scalable okay. 10:37.630 --> 10:40.840 If you add a namespace then you need to change it everywhere. 10:41.410 --> 10:47.770 So in this case I just provide the topic name without the slash. 10:47.770 --> 10:52.690 And well now we're going to have the slash ABC slash my number topic. 10:52.690 --> 10:55.870 We also want to have the same topic name on that side. 10:55.870 --> 10:58.720 So we're also going to add the namespace here. 10:58.720 --> 11:08.260 It's going to make more sense namespace ABC and remove this slash that we've added previously okay. 11:08.290 --> 11:11.200 Now let's run again. 11:11.200 --> 11:18.790 So build and then source and then launch. 11:20.680 --> 11:28.150 And let's uh well let's see with Ross two topic list what's going to happen. 11:28.150 --> 11:30.910 You see we have everything is good. 11:31.150 --> 11:35.890 And we can verify that we've actually graph okay perfect. 11:35.920 --> 11:41.410 Now it's slash ABC my number publisher publishing to slash ABC my number. 11:41.410 --> 11:44.560 And this one is subscribing to the correct topic. 11:44.560 --> 11:52.240 And you see also that topic name here has changed because we've applied the ABC namespace to everything 11:52.240 --> 11:53.630 inside this node. 11:53.630 --> 11:54.740 And for the view here. 11:54.740 --> 11:57.500 Well you see I have put zero for namespaces. 11:57.500 --> 11:59.180 But then you can put one for example. 11:59.180 --> 12:01.760 And it's going to group the nodes inside. 12:01.760 --> 12:05.420 You see boxes that correspond to the namespace. 12:05.420 --> 12:11.690 So depending on some cases sometimes it's going to be more readable like this or more readable. 12:11.690 --> 12:15.170 As you increase this number you can just check on your own. 12:15.200 --> 12:15.770 All right. 12:15.770 --> 12:20.780 And that's going to be it for namespaces and how to apply them in launch files. 12:20.780 --> 12:25.730 So you can see in the end this concept and how to use it is not that complicated. 12:26.000 --> 12:31.790 And just in case you need to add a namespace inside of Python launch file, well, this one is quite 12:31.790 --> 12:32.240 easy. 12:32.270 --> 12:37.460 You see, once you have the structure, you just add a namespace argument here. 12:37.490 --> 12:38.810 Okay, with the namespace. 12:38.810 --> 12:41.840 And what I've done is also remove this slash here. 12:41.870 --> 12:45.590 Same reason as I explained to you in the XML launch file. 12:45.860 --> 12:46.280 Okay. 12:46.280 --> 12:52.640 So just namespace like that is going to do the same thing as this in XML.