WEBVTT 00:00.140 --> 00:06.320 In this laboratory lesson, we will see how to start the simple parameter node and how to use the two 00:06.410 --> 00:12.260 command line interface to interact with the parameters of a node allowing us basically to read them 00:12.260 --> 00:16.760 from the terminal or even to change their values during the execution. 00:17.930 --> 00:18.290 To do. 00:18.290 --> 00:26.720 So let's start by opening a new terminal and go into the workspace and let's source the file setup dot 00:26.720 --> 00:32.720 bash that is in the source folder, that is in the install folder so that the packages that we created 00:32.720 --> 00:37.550 in this workspace are recognized and we can execute them from this terminal. 00:38.030 --> 00:42.260 So let's start by running our simple parameter node with the command. 00:42.260 --> 00:49.070 Ross to run and then I'm going to launch the C plus plus implementation of the simple parameter node. 00:49.070 --> 00:54.050 So I'm going to launch the one from the Arduino, but CP examples. 00:54.050 --> 01:00.530 But if you want to launch the Python one, you need to launch it from the Arduino dot pi examples. 01:00.530 --> 01:06.380 And from this one we can see that there is the simple parameter executable available. 01:06.830 --> 01:12.170 So let's execute this simple parameter node and let's press enter. 01:12.170 --> 01:19.830 And now our node is up and running and so we can actually see and we can check that actually the parameters 01:19.830 --> 01:21.390 of the node are available. 01:21.390 --> 01:27.000 So the node has two parameters and let's check that those are available with the command. 01:27.120 --> 01:29.910 Ros two param a list. 01:30.750 --> 01:38.190 Just as the Ros2 Topic list command provides a list of all the currently available topics in Ros2. 01:38.370 --> 01:45.000 The Ros2 Param List command provides a list of all the parameters that are available for each node. 01:45.030 --> 01:50.670 In this case, we can see that there is only one node active, so the simple parameter node. 01:50.670 --> 01:58.230 And we can also see that apart from some parameters that were instantiated by default so that ros2 is 01:58.230 --> 02:03.320 passing by default to each node that are the quality of service parameters. 02:03.330 --> 02:08.750 We can also see that there are two more parameters and those are the two ones that we have declared. 02:08.760 --> 02:12.690 So the simple int parameter and the simple string parameter. 02:13.110 --> 02:22.050 We can see the values that are associated with these parameters with the command Ros2 param get followed 02:22.050 --> 02:26.010 by the name of the node from which we want to read the parameters. 02:26.010 --> 02:31.990 And so let's read those of the simple parameter node and followed by the name of the parameter that 02:31.990 --> 02:33.070 we want to read. 02:33.100 --> 02:39.490 For example, let's take the simple int parameter and let's press enter. 02:39.490 --> 02:42.700 And as we can see its value is 28. 02:42.700 --> 02:46.240 So it is an integer and its value is 28. 02:46.240 --> 02:50.620 And this is exactly the default value that we assigned to the parameter. 02:50.620 --> 02:56.350 Since when we started the node, we haven't passed any parameter to the node. 02:56.890 --> 03:04.150 Now, if we stop the execution of the node and this time we restart it, but passing a different value 03:04.150 --> 03:07.110 to the simple int parameter. 03:07.120 --> 03:12.190 And so we can do this with the Ros arcs. 03:12.190 --> 03:24.130 And then let's use the flag minus P to pass a new parameter and let's set the simple int param to be 03:24.280 --> 03:26.260 30 this time for example. 03:26.260 --> 03:28.060 So let's press enter. 03:28.060 --> 03:34.510 And now this means that we are starting the simple parameter node, assigning a value to the simple 03:34.510 --> 03:35.410 int parameter. 03:35.680 --> 03:40.390 Here there is an error, so it should be simple int parameter. 03:40.420 --> 03:41.530 Okay, perfect. 03:41.860 --> 03:48.400 And so we basically with this new value 30 it is overriding the default value that was here. 03:48.400 --> 03:57.380 28 And so if we launch again the Ros two param get on the simple int parameter actually we can see that 03:57.380 --> 03:59.060 its value is 30. 04:00.650 --> 04:08.090 Not only we can change our parameter by relaunching the node, so here we add to restart the node to 04:08.090 --> 04:10.670 assign a value to the simple int parameter. 04:10.700 --> 04:13.910 We can also do so while the node is running. 04:14.000 --> 04:17.870 For example, let's do this with the simple string parameter. 04:18.020 --> 04:27.110 First, let's read its current value with the Ros two param get and from the simple parameter let's 04:27.110 --> 04:31.550 read the simple string parameter. 04:32.570 --> 04:36.560 And now for the moment, we can see that the value is Antonio. 04:36.590 --> 04:42.950 That is a string and is exactly the default value that we assigned to this parameter in the code. 04:43.250 --> 04:51.350 And now to change its value, we can use the command ros2 param set still followed by the name of the 04:51.350 --> 04:54.020 node of which we want to change the parameters. 04:54.440 --> 04:59.720 That is the simple parameter followed by the name of the parameter that we want to change. 05:00.170 --> 05:06.200 And so the simple string parameter. 05:06.200 --> 05:08.660 And then we need to assign a new value. 05:08.660 --> 05:12.170 And so as this is a string, let's print for example. 05:12.170 --> 05:18.380 So let's change its value to I ros two and let's press enter. 05:19.070 --> 05:24.950 As soon as we do so, we can see here that our node so the simple parameter gets notified. 05:24.950 --> 05:33.150 So the callback function gets called and we can see that the new value so it is printing the new value 05:33.150 --> 05:40.080 of the simple string parameter that is the string Ros that we have just assigned to this parameter. 05:40.080 --> 05:47.550 And also if we use for example, the Ros two param get again, we can see that the value of the parameter 05:47.550 --> 05:49.530 is not anymore the string. 05:49.530 --> 05:52.680 Antonio but is the string I Ros two. 05:53.610 --> 06:00.660 The Aroostook Command line interface also offers many other commands to interact with the parameters 06:00.660 --> 06:05.130 and you can see the list of them by typing ros2 param. 06:05.340 --> 06:10.020 And then if you use Tab twice you can see the list of all the commands. 06:10.020 --> 06:17.700 So the list of the available commands that you can use to interact with the parameters of a node. 06:17.850 --> 06:24.390 I encourage you to try out some of these as they are quite self explicative and they will help you to 06:24.390 --> 06:27.840 better understand how the parameter works in Ros to.