WEBVTT 00:00.050 --> 00:02.210 What is a Ros2 parameter? 00:02.630 --> 00:05.720 To understand Ros2 parameters, let's start with the problem. 00:05.720 --> 00:10.040 Let's come back to the camera package I used when explaining packages and nodes. 00:10.040 --> 00:13.220 Inside this package we have a camera driver node. 00:13.220 --> 00:14.870 We will focus on that node. 00:14.870 --> 00:17.660 So what does a camera driver node do? 00:17.690 --> 00:22.910 Well, it is expected to connect to a camera through a hardware interface for example USB. 00:22.910 --> 00:25.550 And then get the images from the camera. 00:25.580 --> 00:29.930 Now inside your nodes you will have some variables for settings. 00:29.930 --> 00:36.920 For example, the name of the USB device, the FPS you want to apply, and if you want to run your node 00:36.920 --> 00:39.200 in a simulation mode or not. 00:39.230 --> 00:41.510 Of course you could have many more settings. 00:41.510 --> 00:47.810 So if you want to run your camera and the USB device name is different than the one in the code, well, 00:47.810 --> 00:53.240 you have to change that setting inside your code and build the package again if needed. 00:53.240 --> 00:59.210 If you want to start your camera with 30 fps instead of 60 fps, well, you will have to change the 00:59.210 --> 00:59.990 code again. 00:59.990 --> 01:06.320 And what if you want to run the node twice, once in simulation mode for a certain camera and once in 01:06.320 --> 01:08.060 real mode for another camera? 01:08.090 --> 01:13.730 You would have to duplicate the entire code so you can see that hardcoding those settings into your 01:13.730 --> 01:16.550 code is definitely not a great option. 01:16.550 --> 01:23.660 And here comes Ros two parameters A Ros two parameter is a configuration value for a node, useful for 01:23.660 --> 01:28.480 any kind of setting, So you first need to declare those parameters in your code. 01:28.480 --> 01:32.110 And then when you start the node, you set the values. 01:32.110 --> 01:35.950 So here for example, we start the node and give some values for the parameters. 01:35.950 --> 01:42.100 When we start it with the Ros two run command in the terminal, those values will be set in the code. 01:42.100 --> 01:43.630 So the node can use them. 01:43.630 --> 01:46.180 And we will see how to do that later in this section. 01:46.180 --> 01:51.970 Now if you want you can kill that node and start it again with a different pH value for example. 01:51.970 --> 01:57.340 Or you can start another node with different settings and of course a different name. 01:57.340 --> 01:59.620 If you have two instances of the same node. 01:59.620 --> 02:04.240 And the best part of all that is that you didn't touch anything in the code of the node. 02:04.240 --> 02:07.330 You don't have to compile, you don't have to build anything. 02:07.360 --> 02:11.620 Again, you just need to provide the parameters values at runtime. 02:11.620 --> 02:18.370 So to recap Ros two parameters are used to provide settings for your nodes and you set their values 02:18.400 --> 02:19.510 at runtime. 02:19.540 --> 02:21.940 A parameter is specific to a node. 02:21.940 --> 02:28.300 It will only live while the node is alive, and two different nodes will have two different sets of 02:28.300 --> 02:28.870 parameters. 02:28.870 --> 02:29.590 Values. 02:29.620 --> 02:33.070 A Ros two parameter has a name and a data type. 02:33.100 --> 02:39.580 Among the most common types you can find booleans, integer numbers, double numbers, strings, and 02:39.580 --> 02:41.800 lists of previous data types. 02:41.830 --> 02:47.080 All right, now you are aware of what Ros two parameters are and why we need them. 02:47.080 --> 02:50.230 Let's practice by diving directly into the code.