WEBVTT 00:00.080 --> 00:06.140 In this lesson, we will experiment with turtle SIM so you can practice more with parameters and discover 00:06.140 --> 00:08.570 more command line tools for ros2 params. 00:08.570 --> 00:14.870 It's also a good opportunity to see how you can interact with parameters from existing nodes, where 00:14.870 --> 00:16.370 you don't have access to the code. 00:16.370 --> 00:18.500 So let's start turtle sim here. 00:18.530 --> 00:24.440 Ros to run turtle sim and turtle sim node. 00:24.470 --> 00:25.760 I just need that one. 00:25.760 --> 00:29.480 We want run the Teleop turtle just that one. 00:29.480 --> 00:33.920 And then in that terminal I'm going to run Ros two param list. 00:33.920 --> 00:39.680 So we've already seen that command is going to list all of the parameters for actually all of the nodes. 00:39.680 --> 00:42.800 So you can see we have the turtle SIM node here. 00:42.800 --> 00:46.640 If I do Ros two node list you see we have turtle sim. 00:46.640 --> 00:51.290 So for each node you will get the name of the node and then a colon. 00:51.290 --> 00:53.090 And then you have all the parameters. 00:53.090 --> 00:56.030 So you might see some that we've already seen before. 00:56.060 --> 00:59.840 For example use SIM time start type description service. 00:59.840 --> 01:03.800 Those parameters will exist for all the nodes that you start. 01:03.800 --> 01:08.930 And then we also have this shows Cuz of the rights that we have seen in the C plus plus node. 01:08.930 --> 01:11.360 So basically those parameters. 01:11.390 --> 01:15.650 Well, we exist for almost every node and we can just ignore them for now. 01:15.650 --> 01:22.010 And we can see that in the application in the code itself we have those four parameters okay. 01:22.040 --> 01:22.700 Background. 01:22.730 --> 01:23.750 B background. 01:23.780 --> 01:25.100 G background. 01:25.130 --> 01:30.560 Uh so that's going to be basically to set the background color with a red, green and blue. 01:30.560 --> 01:37.700 And also that one now well once we have all those parameters how can you get the value for one parameter. 01:37.700 --> 01:41.000 Well you have the Ros2 param get. 01:41.000 --> 01:43.010 And you need to provide two things. 01:43.010 --> 01:44.630 First the name of the node. 01:44.630 --> 01:47.810 So the name of the node is slash turtle sim. 01:47.810 --> 01:50.090 And you can use the autocompletion of course. 01:50.090 --> 01:53.270 And then you need to provide the name of the parameter. 01:53.270 --> 01:55.820 So let's say I want that one. 01:56.180 --> 02:02.870 So ros2 get name of the node, the complete name including the slash here, and the name of the parameter. 02:04.040 --> 02:06.800 And you can see we have first the type. 02:06.800 --> 02:12.190 It's an integer value is and you can see it's 86. 02:12.220 --> 02:14.470 Let's do the same thing with the B. 02:14.590 --> 02:17.680 And so the blue and the red. 02:19.270 --> 02:21.580 So you can see we have a red green. 02:21.580 --> 02:26.920 So we have an RGB value for the screen for the background of the screen. 02:26.920 --> 02:31.360 And it seems that it's a number between 0 and 255. 02:31.360 --> 02:34.540 And with this you can see the default values for the parameters. 02:34.540 --> 02:37.870 So actually it means you can modify the value. 02:37.900 --> 02:41.410 You can modify the background color when you start talking. 02:41.440 --> 02:47.350 And by default if you don't provide any parameter, well those values are going to be used because it's 02:47.350 --> 02:52.000 probably what has been declared as default values in the code. 02:52.030 --> 02:54.340 Now let's stop this. 02:54.340 --> 02:55.510 Let's run again. 02:55.540 --> 03:01.660 Let's do ros args, then dash p and let's provide one parameter value. 03:01.660 --> 03:05.500 For example, let's set the background value to zero. 03:05.500 --> 03:10.690 So background underscore b is equal to zero. 03:10.690 --> 03:15.130 If I do this it means that I'm only going to change that parameter here. 03:15.130 --> 03:15.820 And the rest. 03:15.850 --> 03:19.000 So the two other ones will stay at their default values. 03:19.030 --> 03:21.430 I could change all three if I wanted to. 03:22.630 --> 03:25.600 And you can see now the color is completely different. 03:25.630 --> 03:28.330 Well, because I have removed the blue part. 03:28.360 --> 03:34.360 Now if I do so the r you see is still the same. 03:35.230 --> 03:38.140 And then the green is still the same. 03:38.890 --> 03:43.030 And the blue now is zero. 03:43.060 --> 03:45.100 You can see it was 255. 03:45.130 --> 03:47.050 But then I provided a value. 03:47.050 --> 03:48.670 So now it's zero. 03:48.670 --> 03:49.330 And then what. 03:49.330 --> 03:51.610 You can also add another dash. 03:51.640 --> 03:54.850 Be back ground. 03:55.990 --> 03:57.220 Let's say r. 03:58.030 --> 04:00.280 Let's put this one to I don't know 200. 04:00.580 --> 04:03.040 And you can see we have yet another color. 04:03.040 --> 04:08.200 So you can basically choose any color you want with any combination of red, green and blue. 04:08.200 --> 04:13.570 And you can see that's very useful because first of all we didn't need to compile any code again. 04:13.570 --> 04:17.800 And secondly, we actually didn't even need to check the code. 04:17.800 --> 04:19.450 We don't know what's the code of turtles. 04:19.630 --> 04:21.400 We just know they have parameters. 04:21.400 --> 04:24.130 And with those two param lists we can see the list. 04:24.160 --> 04:25.960 We can then get their values. 04:25.960 --> 04:32.020 And we can basically know what we need to provide so that we can start the same node, but with a different 04:32.020 --> 04:32.980 configuration. 04:33.010 --> 04:38.740 Now there is one more thing I'm going to come back to if I do Ros2 service list. 04:38.770 --> 04:40.570 If I list the services. 04:40.810 --> 04:43.360 So those are all the services from the same node. 04:43.390 --> 04:43.660 Okay. 04:43.780 --> 04:45.130 This is just one node. 04:45.130 --> 04:52.720 And you can see that we have all those services, most of them actually using you see parameter stuff. 04:52.720 --> 04:56.680 So I told you that those are services to interact with the parameter functionality. 04:56.710 --> 04:59.710 And now that we are there let's actually see what it is. 04:59.710 --> 05:04.450 So you have a service for example list parameters. 05:05.260 --> 05:12.580 Let's do Ros2 service type to see what is the type of this parameter. 05:13.210 --> 05:17.590 The type is what RCL interfaces service list parameter. 05:17.590 --> 05:20.860 So that's yet a new package that we haven't used yet. 05:20.860 --> 05:32.770 We can do Ros2 interface show with that one and what you see quite a lot of stuff, but basically what 05:32.770 --> 05:38.020 you can just provide an empty request and it's going to return the name. 05:38.020 --> 05:39.730 So the list of all parameters. 05:39.730 --> 05:51.670 So if I do Ros2 service call, the name was turtle sim slash list parameters. 05:51.760 --> 05:58.810 If I forgot to type I just press tab twice I see RCL, so I type RCL okay. 05:58.810 --> 06:02.290 And then I'm just going to omit the request here. 06:03.610 --> 06:10.210 And you see we have a request and the response you see list parameters and we see the background B background 06:10.240 --> 06:12.010 g background R okay. 06:12.040 --> 06:14.890 So you can also use those services. 06:14.890 --> 06:20.620 And that's going to do the same thing as Ros2 param list in this case. 06:21.850 --> 06:24.670 Now you might think why do you want to use those services. 06:24.670 --> 06:26.710 It's much easier with the command line. 06:26.710 --> 06:29.860 Well that's true if you are using the terminal. 06:29.890 --> 06:35.490 But let's say you want to interact within a node with the parameters of another node. 06:35.490 --> 06:39.930 Then you can use the service so you know what's the name of the service. 06:39.960 --> 06:44.370 You know, what's the interface you have seen previously how to create a service client. 06:44.370 --> 06:50.160 So then if you ever want to interact with the parameters of a node from another node, you could do 06:50.160 --> 06:53.370 that using those services here. 06:53.370 --> 06:56.520 So Ros2 service list. 06:56.550 --> 07:03.060 You see we have services for each node so you can interact programmatically with the parameters. 07:03.060 --> 07:06.180 So I just mentioned this here quite quickly. 07:06.180 --> 07:09.960 You will actually not really need to use that that often okay. 07:09.990 --> 07:11.910 I basically almost never use it. 07:11.910 --> 07:16.530 So I would say it's not the most important thing to focus at the beginning, but it's good to know that 07:16.530 --> 07:17.370 you can do that. 07:17.400 --> 07:17.820 All right. 07:17.820 --> 07:23.100 So that's going to be it for the tutorial and parameters I encourage you to practice a bit more okay. 07:23.130 --> 07:27.270 To run the node with different parameters, try different values. 07:27.270 --> 07:33.150 Maybe try to call some of the service here to get, maybe get some parameters and then see the values 07:33.150 --> 07:34.410 for all those parameters here. 07:34.410 --> 07:36.930 Well, you can experiment a bit more on your own.