WEBVTT 00:00.050 --> 00:05.630 In the previous section on tools and with nodes and Ros to run, you have seen that you can rename a 00:05.630 --> 00:07.310 node at runtime. 00:07.310 --> 00:11.720 Well, it's also possible to rename a topic and it's pretty simple. 00:11.720 --> 00:12.980 Let's see how to do that. 00:12.980 --> 00:19.040 So first we are going to use the Ros to run with the package name for example my pi pkg. 00:19.040 --> 00:21.950 And let's start the robot new station. 00:21.950 --> 00:25.670 What you have seen so far I'm going to put that a bit bigger. 00:25.670 --> 00:26.960 What you have seen so far. 00:26.960 --> 00:29.990 How to rename a node for example Ros. 00:30.410 --> 00:39.800 You put Ros args and then dash r and then underscore underscore node and let's name it my station okay. 00:39.830 --> 00:43.160 So you run that you see now the node is my station. 00:43.160 --> 00:46.460 So I can do Ros two node list. 00:46.610 --> 00:47.780 It's called my station. 00:47.780 --> 00:52.340 And if I do Ros two topic list. 00:52.340 --> 00:54.740 So the topic is still robot news okay. 00:54.770 --> 00:56.840 We haven't modified the topic. 00:56.960 --> 01:02.300 Now I'm going to stop and I'm going to run the command again. 01:02.390 --> 01:06.280 But this time I'm also going to rename the topic. 01:06.280 --> 01:07.390 So how to do that? 01:07.420 --> 01:13.150 Well, as I told you, you need to put Ros ARGs, but you only need to put that once. 01:13.180 --> 01:13.600 Okay. 01:13.630 --> 01:14.830 So it's already here. 01:14.860 --> 01:20.560 Then we have one remapping for the node with this underscore underscore node. 01:20.680 --> 01:23.980 To add another remapping you just add another dash R. 01:24.070 --> 01:27.940 And then here well we need to provide the name of the topic. 01:27.940 --> 01:32.200 So what is the name of the topic robot news. 01:32.200 --> 01:33.760 We don't need to provide the slash okay. 01:33.790 --> 01:37.060 It's robot news in the code here. 01:37.510 --> 01:38.200 It's. 01:38.200 --> 01:44.410 So if I go to the Python one you see we have created the robot news topic. 01:44.410 --> 01:50.890 So I put this one here and I put colon equal and I put the new name. 01:51.250 --> 01:52.510 So let's say a b c. 01:52.540 --> 01:58.750 If I press enter now I have renamed the node and also the topic. 01:58.750 --> 02:09.570 So if I do Ros two topic lists you see now we have the ABC topic Okay if I do ros2 topic equal a b c. 02:11.400 --> 02:14.520 You see, that's where we receive the data now. 02:14.580 --> 02:15.090 Okay. 02:15.120 --> 02:18.660 So when you do a remapping of the topic you can see that. 02:19.500 --> 02:25.860 So this string here when you do create publisher it's actually not fixed okay. 02:25.890 --> 02:28.350 It can be changed at runtime. 02:28.350 --> 02:35.940 So this name can be overridden at runtime with that dash R and then the name. 02:35.940 --> 02:37.680 So the previous name and the new name. 02:37.680 --> 02:43.110 So now let's for example let's run here Ros to run my. 02:43.140 --> 02:45.450 So you could run the Python one or the C plus plus one. 02:45.450 --> 02:46.440 It doesn't matter. 02:46.470 --> 02:51.450 Let's run the smartphone node which is subscribing to the robot news station. 02:51.450 --> 02:53.610 So to the robot news topic. 02:53.610 --> 02:55.860 And you see we receive nothing. 02:55.860 --> 02:56.760 Why is that. 02:56.760 --> 03:00.510 Because Ros two topic list. 03:01.080 --> 03:05.010 You see that we have the topic ABC here and we have the topic Robot news. 03:05.010 --> 03:09.110 So if we want to be able to receive the information. 03:09.560 --> 03:14.000 We are also going to do a remapping of the topic. 03:14.000 --> 03:17.300 So we do Dash, Dash, Ross, AGS. 03:17.420 --> 03:21.830 And then here I'm not going to rename the node, I'm just going to rename the topic. 03:21.830 --> 03:28.520 So Dash R robot News colon equal ABC. 03:28.790 --> 03:34.610 I press enter and you can see now we receive the data. 03:34.880 --> 03:35.360 Why. 03:35.390 --> 03:41.180 Because this is a subscriber to ABC and this is a publisher to ABC okay. 03:41.210 --> 03:47.030 So this can be very very useful because if you need to match different nodes written by different persons, 03:47.060 --> 03:52.490 or maybe you can't access the code and you can't modify the topic name in the code. 03:52.490 --> 03:56.510 Well, you just remap the topic name at runtime. 03:56.510 --> 03:57.680 And very important. 03:57.680 --> 04:01.250 Again, you only write the Ros args once. 04:01.250 --> 04:09.890 As you can see here we do two remappings, but we only write ros args once and then dash r and the remapping.