WEBVTT 00:00.050 --> 00:05.060 In this lesson you will see how to introspect your topics with the command line tools. 00:05.060 --> 00:07.520 We will look at the Ros2 topic command line. 00:07.520 --> 00:14.150 In fact, you've already seen two functionalities of that one Ros2 topic list and Ros two topic eco. 00:14.150 --> 00:17.630 So we are going to review them and discover a few new ones. 00:17.630 --> 00:21.530 First of all, what if I do Ros two topic list. 00:21.560 --> 00:23.390 That's going to list all the topics. 00:23.390 --> 00:27.770 So I have well I have parameter events and arose out. 00:27.770 --> 00:31.100 This is because I have run some nodes before. 00:31.100 --> 00:33.620 So if you run that for the first time you will not see this. 00:33.620 --> 00:37.760 But I have run some nodes recently and there is some stuff happening in the background. 00:37.760 --> 00:44.390 So anyway, you will see that every time you start a node, you will also see that you have two topics, 00:44.390 --> 00:46.040 one for parameter events. 00:46.040 --> 00:47.450 So that's for parameter stuffs. 00:47.450 --> 00:50.360 And we're going to see parameter later in this course. 00:50.360 --> 00:52.280 And one is Ros out. 00:52.280 --> 00:59.540 So basically actually when you do a log in a node, anytime you do a log it's also going to be published 00:59.570 --> 01:01.280 to the Ros out topic. 01:01.310 --> 01:01.580 Okay. 01:01.610 --> 01:05.260 You don't see that, but it's actually done in the background. 01:05.260 --> 01:07.840 So now let's do Ros two run. 01:07.840 --> 01:10.630 Let's start a node that has a publisher. 01:10.750 --> 01:17.050 So my Pi PG for example with Robot News Station okay. 01:17.080 --> 01:18.490 It has been started. 01:18.520 --> 01:25.810 Now if I do Ros two topic list, you see we have the robot news and you see if I stop the node and if 01:25.810 --> 01:27.040 I do Ros two topic list. 01:27.040 --> 01:30.310 Again the robot news is gone. 01:30.340 --> 01:30.700 All right. 01:30.730 --> 01:39.250 So you will only see the topic in the list if you have at least one publisher or at least one subscriber 01:39.250 --> 01:40.480 to the topic. 01:40.480 --> 01:45.520 So we can do Ros two topic info with the topic name. 01:45.580 --> 01:48.640 So you find it with the list and then you do info. 01:48.670 --> 01:51.610 The info is going to give us the type. 01:51.610 --> 01:53.920 So we see that this topic. 01:53.950 --> 01:58.030 To publish or subscribe to this topic you need to use this interface. 01:58.030 --> 02:01.450 So example interfaces msg string. 02:01.450 --> 02:07.110 And you see that's exactly what we provided in the code, and we can see we have how many publishers 02:07.110 --> 02:09.990 we have one and we have zero subscriber. 02:10.020 --> 02:14.100 Okay, so Rostopic list and Ross two topic info. 02:14.130 --> 02:20.790 Now you can subscribe directly to a publisher or actually not to a publisher, but to a topic with Ross 02:20.820 --> 02:22.740 two topic equal. 02:22.770 --> 02:23.880 That's quite powerful. 02:23.880 --> 02:27.390 And you're going to provide the name of the topic. 02:27.390 --> 02:35.310 So robot news and in this case you see that I'm going to receive the messages from that publisher here. 02:35.310 --> 02:42.240 If I do a Ross two topic info here, you see we have one publisher, but now we have one subscriber 02:42.240 --> 02:46.980 because that's Ross two topic equal counts as a subscriber. 02:47.010 --> 02:53.640 Okay, if I stop that you see we lose the subscriber okay, so Ross two topic equal is probably one 02:53.640 --> 02:55.620 of the comments that I use the most. 02:55.650 --> 03:00.990 This is very, very useful because when you have a topic, well you find the name etc. but then if you 03:00.990 --> 03:04.700 just want to know quickly what's being published, what's going on in the topic. 03:04.700 --> 03:09.140 You just do a rostopic echo and you have all the data on the terminal. 03:09.140 --> 03:13.010 Then let's continue with the introspection here of the topics. 03:13.010 --> 03:13.790 So you have the list. 03:13.820 --> 03:19.220 You can find the info and then you see in the info you can find the interface. 03:19.250 --> 03:21.980 Now to see what's in the interface. 03:21.980 --> 03:24.140 What's the detail of that. 03:24.140 --> 03:30.170 You will use actually a different command line which is Ros2 interface. 03:30.170 --> 03:34.640 And you have the show keyword here and you need to provide. 03:34.640 --> 03:39.890 So you just take that name here and it's going to show you the detail. 03:39.920 --> 03:43.040 So the implementation of that interface. 03:43.040 --> 03:45.710 So here you can see once again we have some comments. 03:45.740 --> 03:52.010 And we just have one field which is a string data type with a data name okay. 03:52.040 --> 04:00.020 So from the Ros2 topic command line you can find the name of the topic, the type of the topic and what's 04:00.020 --> 04:02.480 exactly inside this type. 04:02.480 --> 04:06.100 Then there are two more commands I want to show you. 04:06.640 --> 04:09.040 So let's clear that. 04:09.160 --> 04:10.660 Let's clear that. 04:11.110 --> 04:13.630 So we still have one publisher running. 04:13.660 --> 04:14.320 Okay. 04:14.350 --> 04:21.760 Now, if you want to know what is the frequency at which messages are published on the topic, you can 04:21.760 --> 04:26.590 use Ross to topic h z for Hertz. 04:26.620 --> 04:27.160 Okay. 04:27.160 --> 04:28.990 And then the name of the topic. 04:29.080 --> 04:33.460 So Robot News that's going to listen to the topic. 04:33.940 --> 04:37.840 So you need to wait a few seconds and it's going to tell you the average rate. 04:37.870 --> 04:38.530 Okay. 04:38.530 --> 04:40.240 So let's control C here. 04:40.240 --> 04:42.640 And you see the average rate is two. 04:42.670 --> 04:43.960 That's two hertz. 04:43.990 --> 04:46.480 Two hertz means 0.5 seconds. 04:46.510 --> 04:46.990 Okay. 04:47.020 --> 04:48.970 And that's exactly what's happening here. 04:49.000 --> 04:54.850 So if you have one topic like this and we know we publish at 0.5 seconds, that's easy to verify. 04:54.850 --> 04:57.850 But then let's say you have several publishers with many different messages. 04:57.850 --> 05:02.950 Then you can have a good idea of how many messages are actually being published every second. 05:02.980 --> 05:05.380 Okay, with this Hz command. 05:05.380 --> 05:10.010 And now if you want to see not the frequency, but if you want to see the bandwidth. 05:10.010 --> 05:12.800 So how much data is actually sent? 05:12.830 --> 05:21.200 You can use Ros2 topic BW for bandwidth and same you provide the topic name. 05:23.000 --> 05:26.690 And so here let's wait a bit is gonna do the same thing. 05:26.690 --> 05:30.650 It's gonna create a subscriber and then print some data. 05:30.650 --> 05:31.610 And you can see. 05:31.610 --> 05:33.140 So that's the average. 05:33.140 --> 05:39.110 You see 100 and something 118 bytes per second. 05:39.110 --> 05:40.700 So that's really not that much here. 05:40.700 --> 05:42.530 We just send some text okay. 05:42.560 --> 05:47.960 But you can see with this how much data is actually sent through the topic. 05:47.990 --> 05:48.500 All right. 05:48.500 --> 05:55.580 So with H, Z and BW you can get more info about how many messages and how big they are. 05:55.610 --> 05:56.180 Great. 05:56.180 --> 06:02.150 And now we have seen how to introspect a topic when you already have some publishers that are running. 06:02.150 --> 06:04.640 But there is also a command you can use. 06:04.670 --> 06:09.340 Let's clear that this is a command you can use to publish on a topic. 06:09.370 --> 06:13.360 You can use rose to topic and then pub. 06:13.930 --> 06:15.220 Okay that's going to publish. 06:15.220 --> 06:17.590 Then you need to provide dash R. 06:17.620 --> 06:18.730 That's going to be the rate. 06:18.760 --> 06:22.000 Let's say I want to publish five times per second. 06:22.000 --> 06:24.430 So I'm going to put dash R five. 06:24.460 --> 06:26.680 After this I need to provide a name. 06:26.680 --> 06:28.960 So I'm going to use slash here. 06:28.990 --> 06:32.230 Robot news okay. 06:32.260 --> 06:33.460 The topic names. 06:33.460 --> 06:35.980 As you can see in the graph they start with a slash. 06:35.980 --> 06:38.260 So in the code you don't need to provide the slash. 06:38.260 --> 06:40.630 It's going to be added automatically for you. 06:40.660 --> 06:40.930 Okay. 06:40.960 --> 06:44.680 So we have dash R and then five and then space. 06:44.680 --> 06:47.140 And then the name of the topic and then space. 06:47.140 --> 06:49.870 And then we have the type. 06:49.900 --> 06:50.110 Okay. 06:50.140 --> 06:55.120 So we have the name and the type for the type we're going to use example interfaces. 06:55.120 --> 06:57.400 And here you can use the auto completion. 06:57.400 --> 06:59.470 It's going to make it much easier. 06:59.470 --> 07:04.750 You can see I just press tab and I have the whole thing for example interfaces msg string. 07:04.750 --> 07:08.790 That's recognized because this topic is using that data type. 07:08.790 --> 07:11.700 And then I need to put double quotes. 07:11.700 --> 07:13.740 And here the syntax is this one. 07:13.740 --> 07:16.170 So curly brackets we have a data field. 07:16.170 --> 07:18.000 And inside we're going to write. 07:18.000 --> 07:21.750 So I'm going to use just single quotes here because we already have double quotes. 07:21.780 --> 07:26.490 Let's say hello from the terminal okay. 07:26.520 --> 07:29.820 So the syntax is a bit more heavy with this comment. 07:29.820 --> 07:36.000 And that's only going to work when you have simple data types like for example this example interface 07:36.000 --> 07:36.690 string. 07:36.720 --> 07:42.960 Because if you have big data types with arrays and classes and subtypes and well, that's not going 07:42.990 --> 07:45.330 to be possible to publish from the terminal okay. 07:45.360 --> 07:47.670 So it only works with very small data types. 07:47.670 --> 07:49.110 So let's press enter. 07:49.830 --> 07:52.320 And you see it's publishing. 07:52.320 --> 07:54.150 So it's publishing on the topic. 07:54.150 --> 08:06.540 Now if I do rose to topic equal with robot news, you see that we're going to receive hello from the 08:06.540 --> 08:07.020 terminal. 08:07.020 --> 08:15.050 And also hi this is the robot from the news station, so we are actually receiving both messages from 08:15.050 --> 08:15.890 both publishers. 08:15.920 --> 08:16.880 Okay, it makes sense. 08:16.880 --> 08:23.240 All the publishers are publishing to a topic, and then from any subscriber we receive all the messages. 08:24.710 --> 08:26.510 So I'm going to stop that and stop that. 08:26.510 --> 08:28.790 Finally one last thing. 08:28.790 --> 08:31.880 So I'm going to clear and clear. 08:31.880 --> 08:34.340 We still have this publisher running. 08:34.340 --> 08:41.240 You can also find informations from the Ros2 node command line okay here we've only used the ros2 topic. 08:41.240 --> 08:46.400 But if you do ros2 node well if you do ros2 node list you will find that node. 08:46.400 --> 08:51.410 Then you do ros2 node info with the node. 08:52.040 --> 09:00.950 And you can see that in the publishers we have robot news topic and the interface name. 09:00.950 --> 09:01.370 Okay. 09:01.400 --> 09:05.480 So you can see you can also find the information using Ros2 node. 09:05.480 --> 09:09.860 So there are many ways you can find the same information from the terminal using the different command 09:09.860 --> 09:10.610 line tools.