1 00:00:01,100 --> 00:00:06,680 In this video we will briefly go over Ross message types, also known as interfaces. 2 00:00:07,160 --> 00:00:13,280 In the last couple of lectures, we made a publisher and subscriber script which used the string message 3 00:00:13,280 --> 00:00:13,880 type. 4 00:00:14,060 --> 00:00:19,520 However, there will be a lot of instances where we want to use other message types to process data 5 00:00:19,520 --> 00:00:21,880 in a more organized way other than string. 6 00:00:21,890 --> 00:00:26,600 So let's head over to the Raw Materials page to see what messages and interfaces entail. 7 00:00:28,180 --> 00:00:32,710 Now you can go ahead and read the background information, but the part I'm most interested in is section 8 00:00:32,710 --> 00:00:33,880 2.1. 9 00:00:33,910 --> 00:00:37,360 Here we can see how a message file in ROS is organized. 10 00:00:37,390 --> 00:00:42,430 Essentially, it is just a basic type available in computer programming associated with a name for the 11 00:00:42,430 --> 00:00:43,030 data. 12 00:00:43,570 --> 00:00:48,130 Ros comes with so many default message types you will most likely want to take advantage of them. 13 00:00:48,130 --> 00:00:54,880 So let's take a look at the standard Messages library, which we use last time to get our string message 14 00:00:54,880 --> 00:00:55,360 type. 15 00:00:55,360 --> 00:00:59,950 So here there are some brief explanations about the messages and the library itself. 16 00:00:59,950 --> 00:01:05,090 And here you have the primitive types which we've been using, including the string. 17 00:01:05,110 --> 00:01:09,640 Now, if I go ahead and right click on this and open it in a new tab, this takes us to the source file, 18 00:01:09,640 --> 00:01:16,180 which, as you can see, is a basic type of string and an attribute name of data. 19 00:01:16,690 --> 00:01:22,630 That's why in our code, when we wanted to utilize the message, we called message dot data to load 20 00:01:22,630 --> 00:01:30,280 in our string Hello world message because that's the attribute name specified by these base message 21 00:01:30,280 --> 00:01:30,970 types. 22 00:01:32,560 --> 00:01:37,810 So here we see in the standard Messages Ross package, we have other basic primitives such as Boolean 23 00:01:37,810 --> 00:01:41,800 floats and even some arrays of those basic types. 24 00:01:41,830 --> 00:01:47,110 To use them, all we have to do is add it to what is imported in our Python script as such. 25 00:01:50,930 --> 00:01:54,660 And then we could use it the same way we're using our string message type. 26 00:01:54,680 --> 00:02:01,070 Let's take a look at another set of commonly used rasp messages use with robots called sensor messages. 27 00:02:01,640 --> 00:02:03,080 So I'll go ahead and scroll down. 28 00:02:05,840 --> 00:02:09,500 Here we see various message types use with common sensors. 29 00:02:09,500 --> 00:02:10,700 You would put on a robot. 30 00:02:11,030 --> 00:02:15,860 For starters, you probably want a camera on your robot so you can see what is going on here. 31 00:02:15,860 --> 00:02:21,050 The image and compressed image message types would be useful as they efficiently send the image pixel 32 00:02:21,050 --> 00:02:22,430 data over ROS. 33 00:02:22,580 --> 00:02:28,670 If you have a GPS on your robot nav, stat fix would be of use as it displays latitude, longitude and 34 00:02:28,670 --> 00:02:30,890 your variances if they are available. 35 00:02:31,400 --> 00:02:33,770 There are also message types for laser scan. 36 00:02:33,770 --> 00:02:35,840 If you have a single point light or point cloud. 37 00:02:35,840 --> 00:02:38,390 If you have a 3D leader, I am. 38 00:02:38,390 --> 00:02:39,230 You is of course good. 39 00:02:39,230 --> 00:02:45,080 If you have an IMU giving you acceleration and orientation data of your robot to include it in our Python 40 00:02:45,080 --> 00:02:50,450 scripts, we can simply call the sensor messages library and import any other messages you are interested 41 00:02:50,450 --> 00:02:52,190 in that's mentioned in that list. 42 00:02:54,080 --> 00:02:59,300 Can also list what message types are available in your current terminal environment by running the ROS 43 00:02:59,300 --> 00:03:01,070 to interface list command. 44 00:03:04,590 --> 00:03:09,250 Here we are given a long list which contains different message types from different packages. 45 00:03:09,270 --> 00:03:12,270 It's organized into three sections messages. 46 00:03:14,670 --> 00:03:17,700 Services and actions. 47 00:03:17,820 --> 00:03:20,640 Messages are used by publishers and subscribers. 48 00:03:20,820 --> 00:03:26,160 Service and action interface corresponds to utilizing that particular service or action. 49 00:03:26,400 --> 00:03:29,060 Feel free to look through the different message types that are available. 50 00:03:29,070 --> 00:03:31,770 But for now, let's review what we went over. 51 00:03:33,090 --> 00:03:36,060 In this lecture, we talked about interface types. 52 00:03:36,180 --> 00:03:40,950 We were able to look at different interfaces that are readily available to us by running the ROS to 53 00:03:40,950 --> 00:03:42,690 interface list command. 54 00:03:43,110 --> 00:03:47,730 We then took some time to look at some commonly used interfaces from the standard messages and sensor 55 00:03:47,730 --> 00:03:48,270 messages. 56 00:03:48,270 --> 00:03:50,460 ROS Packages centered messages. 57 00:03:50,460 --> 00:03:54,090 The collection of primitive ROS data types similar to computer programming. 58 00:03:54,090 --> 00:03:59,640 While sensory messages is a popular message library related to commonly used robot sensors.