WEBVTT 00:00.050 --> 00:02.510 This is an extra lesson that I wanted to add. 00:02.510 --> 00:08.690 And here I'm going to talk about Ross two bags, which can be very useful when working with topics. 00:08.690 --> 00:14.000 So this is more of a parenthesis in this course, and it's the only time I will talk about bags so you 00:14.000 --> 00:16.220 can see it as a bonus. 00:16.220 --> 00:21.260 And to understand what bags are and why we need them, let's start with the problem. 00:21.260 --> 00:22.640 Let's use an example. 00:22.640 --> 00:28.040 Let's say you need to test a robot outside so you have a mobile robot or whatever robot. 00:28.070 --> 00:31.640 You need to test your robot outside when it's raining. 00:31.640 --> 00:37.670 And let's say you are working in a university or in a workplace, but then let's say, well, you don't 00:37.670 --> 00:39.350 have access to the robot all the time. 00:39.350 --> 00:45.260 Maybe you cannot take it outside all the time, and maybe when you take it outside, it's not necessarily 00:45.260 --> 00:46.850 raining all the time. 00:46.850 --> 00:52.520 So that's going to be a problem, especially if you need to develop a feature to improve the robot behavior 00:52.520 --> 00:54.470 when it's raining outside. 00:54.470 --> 00:59.210 And so instead of waiting every time that you have access to the robot, that you can take it outside 00:59.210 --> 01:04.510 and that it's raining, what you could do is to run the experiment once. 01:04.510 --> 01:10.480 So let's say you take it one hour outside when it's raining, you run the experiment once and you save 01:10.480 --> 01:12.130 all the data from the topics. 01:12.130 --> 01:16.960 So for example, if you have a camera topic, if you have will topics, while all the topics that you 01:16.960 --> 01:21.310 have in your applications, you could save the ones that you want inside the data set. 01:21.310 --> 01:27.520 And then you could replay this data set later on, and then you could develop the feature of your application 01:27.520 --> 01:29.050 for this data set. 01:29.080 --> 01:29.200 Okay. 01:29.200 --> 01:30.880 That's going to be much more convenient. 01:30.880 --> 01:33.640 And that's exactly what bags allow you to do. 01:33.640 --> 01:40.750 So with a Ros2 bag, you can save the data from a topic for any amount of time you want, and then you 01:40.750 --> 01:44.710 can replay this data as many times as you want. 01:44.710 --> 01:46.570 And let's see how to do that. 01:46.570 --> 01:50.830 So first of all we will need a publisher okay. 01:50.860 --> 01:55.780 So I'm going to start the publisher we just had from the previous activity. 01:55.810 --> 01:59.620 I'm going to start here Ros to run my pip pig. 01:59.920 --> 02:02.550 And let's start the number. 02:02.850 --> 02:03.930 Publisher. 02:05.490 --> 02:07.680 So that's going to publish on a number topic. 02:07.680 --> 02:16.830 And I'm also going to start here to run my Pi PG number counter. 02:16.830 --> 02:18.090 So here we have a subscriber. 02:18.090 --> 02:20.340 And we also have another publisher. 02:20.340 --> 02:27.180 If I do roster topic list you can see that we have a number topic and a number count topic okay. 02:27.210 --> 02:31.830 So let's say we want to save one of those topics or the two of them. 02:31.830 --> 02:35.220 So I am now in my home directory. 02:35.220 --> 02:42.630 Let's create well let's keep things organized I'm going to create a folder named bags okay. 02:42.660 --> 02:47.010 And we're going to save the bags in that folder just so they are not everywhere. 02:47.010 --> 02:49.920 And then we have the Ros2 command line tool if you remember. 02:49.920 --> 02:52.710 And in this command line we also have Ros2 bag. 02:52.710 --> 02:55.320 And with Ros2 bag you can do dash h. 02:55.320 --> 02:59.040 And of course you have all of the possible commands. 02:59.070 --> 02:59.700 Okay. 03:00.240 --> 03:04.450 So here I'm going to do Ros2 bag and how to record a topic. 03:04.450 --> 03:08.920 I'm going to do record, and then I need to provide the name of a topic. 03:08.920 --> 03:11.980 So let's do a Ross two topic list again here. 03:12.700 --> 03:16.120 Let's say I want to save the number count topic. 03:16.120 --> 03:21.370 So I'm going to do record and then slash number count. 03:21.400 --> 03:22.930 Let's press enter. 03:23.290 --> 03:26.410 And you see we have a lot of stuff here. 03:26.410 --> 03:29.110 So it's listening for topics. 03:29.110 --> 03:32.950 You see we have subscribed to the topic number count okay. 03:32.980 --> 03:34.420 It's recording. 03:34.420 --> 03:36.880 And well you see it's hanging in there. 03:36.880 --> 03:38.620 So it's going to record. 03:38.680 --> 03:43.540 As long as this is running then you can press Ctrl C. 03:43.540 --> 03:48.160 And when you press Ctrl C you see that the recording has stopped. 03:48.160 --> 03:53.680 And here from the logs it seems you see I had 64 and 84. 03:53.680 --> 04:00.880 So I have recorded for about 20s, which means that all the data that was published on that number count 04:00.910 --> 04:05.520 topic for those 20s are now recorded inside a bag. 04:05.520 --> 04:06.540 And if I do lose? 04:06.540 --> 04:09.660 You see, I have a Ross bag here with a time stamp. 04:09.660 --> 04:12.330 So if I go inside, what do we have? 04:12.660 --> 04:18.870 Well, you see, we have some information and the data itself with a map file. 04:18.870 --> 04:22.290 So that's going to contain all of the topics you have saved. 04:22.890 --> 04:26.880 And if I show what's in this metadata.yaml. 04:27.900 --> 04:35.460 Well you can find for example, well the duration in nanoseconds, the starting time and then the different 04:35.490 --> 04:36.780 topics that we have saved. 04:36.780 --> 04:43.260 So you see here we have saved the number count topic with the type and then how many messages we have 04:43.260 --> 04:43.740 saved. 04:43.740 --> 04:48.480 You see we have saved 20 messages and a bit more stuff. 04:48.720 --> 04:50.310 Let's clear that. 04:51.360 --> 04:53.100 Let's go back to our bikes folder. 04:53.100 --> 04:56.220 So we don't really need to go inside the bike itself. 04:56.220 --> 04:57.240 But now you know that. 04:57.270 --> 05:02.400 Well, in this bag we have a YAML file with some information and then the messages. 05:02.760 --> 05:06.440 Now let's start this command again. 05:07.190 --> 05:08.900 So Rose two bike record. 05:08.900 --> 05:14.180 And let's add here a dash o option with test. 05:14.180 --> 05:19.070 Because here by default is going to do rosbag two and then a timestamp. 05:19.070 --> 05:24.470 But you can do a dash o to provide the output name okay. 05:24.500 --> 05:29.660 So for example here I'm going to record for a few seconds and then press control C. 05:29.660 --> 05:33.110 And you see I have the test folder okay. 05:33.110 --> 05:36.500 So you can rename the bag with dash o. 05:36.500 --> 05:38.330 And then you should only have. 05:38.330 --> 05:42.950 Well if you're going to record again you see the folder already exists. 05:42.950 --> 05:44.570 So you need to give a new name. 05:44.600 --> 05:44.960 All right. 05:44.990 --> 05:47.570 So test one for example. 05:47.870 --> 05:49.550 And then control C. 05:49.550 --> 05:52.850 And you see we have our test and test one folder. 05:52.850 --> 05:58.730 You can do rose two bag info as well with for example test. 05:58.730 --> 06:01.040 So you just provide the folder name. 06:01.400 --> 06:04.750 And you can see here actually well we have the back side. 06:04.750 --> 06:10.330 We have the duration, the start, the end, the number of messages, the topics we have saved with 06:10.330 --> 06:11.710 the data type, etc.. 06:11.710 --> 06:17.740 So you see what we saw before in this YAML file that's saved inside the folder. 06:17.740 --> 06:22.120 What we find basically the same information here, but more readable. 06:22.120 --> 06:23.920 So you don't even need to go inside. 06:23.920 --> 06:27.040 You just do Ross Toolbag info and you get the same information. 06:27.040 --> 06:30.310 And then now you know how to record topics inside the bag. 06:30.310 --> 06:38.290 How to play a bag again, you can do Ross to bag and then play and then just the name. 06:38.290 --> 06:41.950 So for example test is going to replay. 06:42.370 --> 06:47.530 So you see here it's starting playback and it's ending with just a few seconds okay. 06:47.560 --> 06:53.050 So it's going to replay and publish again all the data that was received on that topic. 06:53.050 --> 06:54.130 Let's do a. 06:54.160 --> 07:01.150 So let's do a Ross two topic equal number count okay. 07:01.180 --> 07:05.200 So here we have what we have this node here I'm going to stop all the nodes. 07:05.230 --> 07:12.460 Okay, so now we don't have anything publishing on that number count. 07:12.490 --> 07:13.270 As you can see. 07:13.270 --> 07:17.590 And I'm going to do Ros2 bag play. 07:17.590 --> 07:21.910 And I'm going to play the first one that I have recorded, this one. 07:21.910 --> 07:25.090 So Rosbag two with a timestamp. 07:25.090 --> 07:27.250 And let's press enter. 07:27.580 --> 07:31.990 And you see now we receive the data here on the number count topic. 07:31.990 --> 07:36.670 And you see at this time the counter was at 180. 07:36.700 --> 07:44.050 And then it's continuing to be published for that one was for 20s. 07:44.710 --> 07:46.330 So let's wait a bit more. 07:46.570 --> 07:50.710 And you see, after 20s the bag stops. 07:50.710 --> 07:57.100 So the ros2 bag play command stops and we have received 20 messages. 07:57.130 --> 07:57.490 All right. 07:57.520 --> 08:03.370 So everything you have recorded at that time is going to be published exactly as it was, because you 08:03.370 --> 08:10.960 can see we were reaching 750 for the number count with the number counter node, but when we recode 08:10.960 --> 08:12.730 it, it was 180. 08:12.730 --> 08:16.330 So we are playing back the data that was at that time. 08:16.630 --> 08:18.250 And so you can see that's very useful. 08:18.250 --> 08:23.260 You can just play the data exactly as it was when you tested your robot. 08:23.260 --> 08:34.300 And finally, let's so let's, uh, run the publisher and the counter again and let's do a Ros two bag 08:35.380 --> 08:37.030 and recode again. 08:38.380 --> 08:43.780 So recode and then oh, let's name it test two. 08:44.140 --> 08:52.300 And then, well, you have seen that you can use a topic name, but you can also provide several topic 08:52.300 --> 08:53.020 names okay. 08:53.050 --> 08:54.880 So number count and number. 08:54.910 --> 09:01.480 In this case I'm going to record you see subscribe to topic number count and subscribe to topic number. 09:01.480 --> 09:03.970 So you can record several topics. 09:04.000 --> 09:07.290 I'm going to press Ctrl I'll see if I do. 09:07.380 --> 09:10.290 Let's put that a bit bigger if I do. 09:10.320 --> 09:14.550 Ross to bag info test two. 09:14.910 --> 09:19.650 You see, we have two topics with nine messages for each. 09:19.650 --> 09:25.320 So if you're going to replay, that bag is going to replay all of the topics that you saved. 09:25.320 --> 09:32.460 And finally you can also just do dash A if you want to record all of the topic. 09:33.450 --> 09:34.860 So in this case what. 09:34.890 --> 09:36.660 Test two is already existing. 09:36.660 --> 09:38.400 I'm going to put test three. 09:39.000 --> 09:43.980 And you see now it's subscribing to all of the existing topics. 09:44.160 --> 09:46.140 Okay I'm going to press Ctrl C. 09:46.140 --> 09:50.970 And then if I do Ross two back info test three. 09:51.270 --> 09:52.920 You see we have the number topic. 09:52.920 --> 09:56.640 We even have extra topics that we didn't even see before. 09:57.030 --> 09:57.390 Okay. 09:57.420 --> 09:58.050 Number count. 09:58.080 --> 10:01.110 We have the parameter events and the rows out. 10:01.140 --> 10:02.520 All right so that's it for Ross. 10:02.520 --> 10:02.910 Two bags. 10:02.910 --> 10:06.630 And as you can see that can be a very useful functionality.