WEBVTT 00:00.140 --> 00:07.430 Now that we have modeled our robot following the Urdf convention, we can move on and visualize it using 00:07.430 --> 00:10.460 one of the most useful tools available in Ros two. 00:10.940 --> 00:12.950 We are talking about RVs. 00:13.910 --> 00:19.100 RV indicates the second version of the Ros visualization tool. 00:19.100 --> 00:26.300 And this is a graphical interface that allows us to visualize the content of some Ros two messages that 00:26.300 --> 00:28.370 are published on some topics. 00:29.360 --> 00:36.230 The way it works is very simple, and it basically uses the publisher subscriber communication protocol. 00:36.590 --> 00:44.540 In fact, are these creates a subscriber node that receives messages from one or more ros2 topics. 00:45.330 --> 00:52.890 Whenever a new message is published on a topic, the subscriber receives it and interprets it based 00:52.890 --> 00:59.550 on the message type, and then it displays it in the GUI in an understandable and intuitive way. 01:00.430 --> 01:06.310 Arby's provides several plugins for the visualization of the most common rescue messages. 01:06.760 --> 01:13.330 For example, it is possible to visualize the map of a building that the robot can use for the navigation 01:13.330 --> 01:21.340 purposes in which three areas are marked in white occupied areas are marked in black and unknown areas 01:21.340 --> 01:24.280 or unexploited areas are marked in gray. 01:25.860 --> 01:32.820 It is also possible to visualize data from the robot sensors such as laser scanner, that measure the 01:32.820 --> 01:34.610 distance from obstacles. 01:34.620 --> 01:42.210 And that you can see here in Irvis represented as a set of red points or even it is possible to visualize 01:42.210 --> 01:47.220 images coming from the cameras that might be mounted on the robot. 01:48.700 --> 01:55.990 All of this information that we can visualize with RVs are basically transmitted as standard rescue 01:56.020 --> 01:58.800 messages in some ros2 topic. 01:58.810 --> 02:06.820 And so arviz simply allows us to visualize such messages with plugins that can interpret the message 02:06.820 --> 02:11.320 and create an understandable and user friendly visualization for it. 02:11.950 --> 02:18.400 I will try to give you some more examples to convince you that this is a key tool in the hands of any 02:18.400 --> 02:22.690 robotic software developer and that you will always find yourself using it. 02:23.110 --> 02:29.290 For this reason, I want to introduce you to this tool so early in the course so that you have time 02:29.290 --> 02:31.780 to play and to experiment with it. 02:32.750 --> 02:39.440 Until now, we have worked only with string messages in Ros2 and so with messages that were really simple 02:39.440 --> 02:45.980 to read and visualize in the terminal just by using the command Ros2 topic Echo. 02:46.190 --> 02:53.510 And so actually we didn't need to use a graphical interface like Arviz to visualize this kind of information. 02:54.080 --> 03:00.380 However, very often the messages that pass in the topics can be very complex and almost impossible 03:00.380 --> 03:05.060 to read and to understand only by displaying their content in the terminal. 03:05.720 --> 03:07.720 For example, this is what happened. 03:07.730 --> 03:15.740 If we use the command Ros2 topic echo to read the content of a topic where a map message is being published. 03:16.580 --> 03:17.960 The message Thatrillionepresents. 03:17.990 --> 03:25.310 A map is called occupancy grid and contains a very long vector full of numbers, each of them representing 03:25.310 --> 03:32.270 a single cell, a single pixel of the map, and also it has a number associated with it that indicates 03:32.270 --> 03:37.460 if the area of the map is free, occupied by an obstacle or unknown. 03:37.460 --> 03:39.020 So still unexplored. 03:40.170 --> 03:46.380 Let's assume that you implemented your code that adds some obstacles to the map and you want to actually 03:46.380 --> 03:47.580 see that it works. 03:47.580 --> 03:52.200 And so that these obstacles have been added in the correct position of the map. 03:52.960 --> 03:59.380 It would be impossible for you to do so only by reading the message in the terminal, just using the 03:59.380 --> 04:06.400 command Ros2 topic echo and by reading one by one each value each pixel of the map. 04:06.820 --> 04:14.650 For this reason, we use RVs to view in a clearer and more understandable way the content of this message. 04:15.970 --> 04:20.090 Similarly in the Ross, two topics can also be published. 04:20.110 --> 04:24.910 All those messages that contain the sensor readings such as laser scanner. 04:25.360 --> 04:30.940 Also in this case, the message that is published in the scan topic is incomprehensible. 04:30.940 --> 04:37.810 If you just read its content in the console, since it contains the distances from the obstacles in 04:37.810 --> 04:41.050 all the directions that are detected by the laser scanner. 04:42.080 --> 04:48.530 Finally, if I still haven't convinced you to use our reach to analyze all the messages that are published 04:48.530 --> 04:55.370 in the two topics, consider also that this not only allows you to visualize the difficult messages 04:55.370 --> 05:02.780 to understand, but it also does that when these messages are being published with high frequency in 05:02.780 --> 05:08.660 those two topics, consider, for example, the case of the streaming video coming from a camera. 05:09.260 --> 05:15.950 In this case, not only you have a message that is difficult to understand since it contains RGB colors 05:15.980 --> 05:20.990 of each pixel of the image, but also since we are dealing with a streaming video. 05:21.020 --> 05:28.130 This is obtained by constantly publishing images frames with high frequency inside the topic. 05:28.880 --> 05:35.360 In the following lessons of this section, we will use this tool to visualize our RDF model of the robot, 05:35.360 --> 05:42.020 and then along the course we will continue using it to visualize other messages that are still published, 05:42.020 --> 05:44.570 still available in some Ros topics.