WEBVTT 00:00.460 --> 00:08.410 In this laboratory lesson, we will use some tools from the TF2 library in Ros2 to create a Python service 00:08.410 --> 00:15.700 server that converts the orientation of an object from its quaternion representation to Euler angles, 00:15.700 --> 00:17.140 and vice versa. 00:17.590 --> 00:20.500 This service can be useful throughout the course. 00:20.500 --> 00:27.070 Whenever you want to know the Euler angles corresponding to a given quaternion, or also vice versa. 00:27.520 --> 00:32.250 Let's create this new tool within a new package in our workspace. 00:32.320 --> 00:39.550 So let's navigate to the workspace and then to the source folder in which we have already created several 00:39.550 --> 00:44.620 packages, and which contains the functionalities that we developed for the robot so far. 00:44.620 --> 00:46.750 And here let's create a new package. 00:46.750 --> 00:53.980 So with the command Ros2 package create let's use as a build type. 00:54.610 --> 00:56.440 Amend CMake. 00:56.440 --> 01:01.240 Since we will be including both Python and C plus plus code in this package. 01:01.240 --> 01:10.150 So let's use CMake as build type and let's name this package Arduino bot utils. 01:10.150 --> 01:13.300 So let's press enter to create this package. 01:13.300 --> 01:15.220 And now back to the workspace. 01:15.220 --> 01:23.110 Let's build the workspace so we can build in order for us to recognize also the newly created package. 01:23.110 --> 01:25.690 So the Arduino bot utils package. 01:27.320 --> 01:30.050 Now we can go back to Visual Studio Code. 01:30.260 --> 01:35.570 And so here we can see that in our workspace there is the Arduino bot utils package. 01:35.960 --> 01:42.350 And conventionally, as we are going to write Python code, this should be placed in a folder within 01:42.350 --> 01:45.860 the package that has the same name of the package itself. 01:46.100 --> 01:52.760 Normally in the previous laboratory lessons, when we developed some Python code, this folder was automatically 01:52.760 --> 01:55.700 created by the build type amend Python. 01:55.820 --> 02:01.610 And so here, for example, for the Arduino Pi examples, we can see that the Arduino bot Pi examples 02:01.610 --> 02:05.870 sub folder was automatically created by the build type that we choose. 02:06.110 --> 02:13.130 Anyway, as for the Arduino bot utils, we are going to include both C plus plus and Python script within 02:13.130 --> 02:14.120 the same package. 02:14.120 --> 02:22.550 So within the Arduino bot utils package we choose cmake as build type and so this is not created automatically. 02:22.550 --> 02:26.210 The folders that we need in order to develop Python code. 02:26.210 --> 02:32.660 So let's start by creating a new folder that is called Arduino bot utils. 02:32.660 --> 02:39.440 And within this folder let's create a new Python file called init dot pi. 02:39.440 --> 02:43.160 And for the moment we can leave this file empty. 02:43.400 --> 02:46.460 And now let's create another Python file. 02:46.460 --> 02:48.260 So the actual node. 02:48.260 --> 02:51.140 So the script that will contain the actual logic of the node. 02:51.440 --> 02:55.790 And so here let's name this one angle. 02:57.830 --> 03:00.080 Conversion dot pi. 03:00.560 --> 03:01.130 Here. 03:01.130 --> 03:05.450 To start the script we need to declare the Python interpreter directory. 03:05.450 --> 03:14.990 Since the CMake build type that we used cannot automatically locate it, so it can be found under the 03:14.990 --> 03:15.920 user. 03:17.130 --> 03:20.220 Been environment. 03:20.220 --> 03:23.160 And the Python version that we are using is Python three. 03:23.310 --> 03:26.520 So Python three. 03:27.340 --> 03:34.030 Now we can proceed as usual in order to create a new two node in which we can instantiate two service 03:34.030 --> 03:41.440 server one will be used for the conversion from quaternion to Euler angles, and the second one will 03:41.440 --> 03:48.130 be used for the conversion between Euler angles to quaternion instead of rewriting the code that we 03:48.130 --> 03:49.210 are already familiar with. 03:49.240 --> 03:55.660 So, for example, the one of the service servers, we can copy directly the contents of the simple 03:55.660 --> 04:00.160 service server that we implemented in the Arduino Pi examples. 04:00.160 --> 04:03.880 And so this script is called the simple service server dot Pi. 04:03.880 --> 04:10.480 So we can copy all the content of this file and we can paste it here. 04:11.050 --> 04:12.880 Let's change the name of the class. 04:12.880 --> 04:18.490 And so let's name this one angles converter. 04:19.450 --> 04:21.990 And then let's also call the node. 04:22.000 --> 04:24.190 So this one angle. 04:26.320 --> 04:27.280 Conversion. 04:29.650 --> 04:31.090 Service server. 04:31.330 --> 04:35.590 And then we need to create two instances of a service server. 04:35.590 --> 04:38.800 So we can copy this instruction here. 04:39.130 --> 04:45.130 And we can paste it below in order to start this node and make it create a new service server. 04:45.930 --> 04:47.340 Let's call the first one. 04:47.340 --> 04:51.300 So this one Euler two. 04:54.110 --> 04:55.010 Quaternion. 04:55.400 --> 05:03.800 And the second one, as you might imagine, quaternion to Euler. 05:04.250 --> 05:05.510 And so the first one. 05:05.510 --> 05:11.960 So the variable Euler to quaternion contains an implementation of a service server that we can call 05:11.990 --> 05:13.550 Euler to quaternion. 05:13.550 --> 05:15.320 So let's copy this one. 05:15.710 --> 05:19.370 And also the name of this server will be Euler to quaternion. 05:19.370 --> 05:25.400 So all the other Ros to nodes and application that want to use this service have to contact it. 05:25.400 --> 05:29.840 So I have to send a request to this service called Yola to quaternion. 05:29.840 --> 05:36.080 And the second one as you might imagine, let's call it quaternion to Euler. 05:36.650 --> 05:40.130 Let's also change the name of the callback function. 05:40.130 --> 05:51.950 So in this case for the Euler to quaternion, the function is the Euler to quaternion callback, and 05:51.950 --> 06:01.790 in the second case we want to execute the quaternion to Euler callback function. 06:01.790 --> 06:08.840 So these are the names of the two callback functions that will be executed when we call the Euler to 06:08.840 --> 06:11.510 quaternion or the quaternion to Euler. 06:11.780 --> 06:15.800 So here let's also change the message that we are printing in the console. 06:15.800 --> 06:19.790 And let's simply say angle. 06:22.190 --> 06:28.610 Conversion services are ready so that we know that both of these services are ready. 06:29.580 --> 06:33.030 Now let's start by defining the callback functions. 06:33.180 --> 06:37.990 So here the one that was called service callback in the example. 06:38.010 --> 06:45.130 Let's name it Yolov2 quaternion and it still receives a request message and our response message. 06:45.150 --> 06:50.760 So for the moment let's leave the content empty. 06:50.910 --> 06:53.100 And let's also define the second one. 06:53.970 --> 06:55.770 So let's define the. 06:56.690 --> 06:59.150 Quaternion to Euler callback. 06:59.270 --> 07:04.580 So this one, and also in this case it receives a request and response message as. 07:04.580 --> 07:05.480 These two are. 07:05.480 --> 07:07.790 Callback function of a service server. 07:08.630 --> 07:12.990 Before moving on to define the logic of the two callback functions. 07:13.010 --> 07:18.200 As you might remember, we have to define the communication interface that the two services use. 07:18.230 --> 07:25.820 That is how the request and response messages are structured for the interaction with these two servers. 07:26.150 --> 07:33.080 We can define these interfaces as we did in the previous lessons in the Arduino bot messages package. 07:33.080 --> 07:38.210 So this package in which we are inserting all the two message interfaces. 07:38.210 --> 07:44.640 And so in the SRV folder in which we have already created the add two interface. 07:44.660 --> 07:54.320 Let's create a new file and let's call this one angular two quaternion dot. 07:56.480 --> 08:02.480 And here let's start by defining the request message of the server. 08:02.480 --> 08:05.630 So the client will send this request message. 08:05.630 --> 08:08.590 And this should contain three Euler angles. 08:08.720 --> 08:12.650 So the three Euler angles that we want to convert into a quaternion. 08:12.650 --> 08:16.060 And so all of these three are decimal numbers. 08:16.070 --> 08:18.500 So let's use float 64. 08:18.710 --> 08:20.150 And these are the roll. 08:23.490 --> 08:24.210 The pitch. 08:26.450 --> 08:28.820 And the yo angles. 08:29.150 --> 08:31.930 And then let's also define the response message. 08:31.940 --> 08:34.310 So let's separate with three dashes. 08:35.390 --> 08:37.790 Let's define the response message. 08:37.790 --> 08:40.730 And this one will contain the converted quaternion. 08:40.730 --> 08:46.310 So this should contain the four elements of the quaternion that are the result of the conversion. 08:46.310 --> 08:48.950 And also these four are decimal numbers. 08:49.220 --> 08:51.950 So let's still use float 64. 08:51.950 --> 08:55.640 And let's call this 1XY. 08:59.960 --> 09:00.470 That. 09:02.050 --> 09:02.740 N.W.. 09:03.190 --> 09:11.110 And so this is what we need for the service user to quaternion to convert the Euler angles that we receive 09:11.110 --> 09:15.280 in input in the quaternion that we want to provide as output. 09:15.400 --> 09:17.440 Let's create also the second interface. 09:17.440 --> 09:21.550 So the one for the communication with the quaternion to Euler service. 09:21.550 --> 09:22.270 So still. 09:22.270 --> 09:30.070 Here let's create a new file called quaternion to user dot serve. 09:30.550 --> 09:33.400 And here in the request message. 09:36.920 --> 09:42.890 And this contains the four elements of the quaternion that we want to convert into Euler angles. 09:43.040 --> 09:51.650 So we can, for example, copy the response message of the Euler to quaternion and paste it here. 09:52.040 --> 09:54.770 Then let's also define the response message. 09:57.480 --> 10:02.600 And this should contain the three Euler angles that are the result of the conversion. 10:02.610 --> 10:07.890 So once again let's copy the three Euler angles. 10:07.890 --> 10:09.330 So roll, pitch and yaw. 10:09.810 --> 10:16.770 And with this we have finished with the definition of these two message interfaces with the two service 10:16.770 --> 10:17.400 server. 10:17.880 --> 10:23.060 Finally, we need to make these messages recognized and compiled in Ros two. 10:23.070 --> 10:26.430 And so we need to add them to the cmake list dot. 10:26.430 --> 10:29.880 TXT file of the Arduino bot messages package. 10:29.880 --> 10:35.090 So here what we have already defined the add two service. 10:35.100 --> 10:39.900 Let's define a new service that is the Euler. 10:40.910 --> 10:41.330 To. 10:43.940 --> 10:56.510 quaternion.sv and then another service that is the quaternion to euler.sv. 10:57.050 --> 10:58.790 Let's save this file. 10:59.210 --> 11:06.920 And now before using these two interfaces within our angle conversion service, let's open a new terminal. 11:07.560 --> 11:15.930 And let's go to the workspace and let's build it so that the new interfaces are also built and compiled 11:15.930 --> 11:17.940 and are recognized in Ros two. 11:17.970 --> 11:20.940 And so we can start using them in our nodes. 11:20.940 --> 11:23.670 So in our angle conversion node. 11:23.820 --> 11:27.600 So once this is done we can go back to Visual Studio Code. 11:27.600 --> 11:30.470 And here we can start using the interfaces. 11:30.480 --> 11:37.650 So this time still from the Arduino but messages package from the SRB folder instead of the Arduino. 11:37.830 --> 11:49.590 Let's import the Euler to quaternion and also the quaternion to Euler. 11:50.400 --> 11:52.020 Let's use the first one. 11:52.020 --> 11:54.630 So the Euler to quaternion interface. 11:54.630 --> 11:58.710 In order to define the interface with the first service server. 11:58.710 --> 12:01.710 So the one that we called Euler to quaternion. 12:01.710 --> 12:05.520 And then let's use the second one to define the second interface. 12:05.670 --> 12:10.110 So here the one with the service quaternion to Euler. 12:10.650 --> 12:14.010 Now we can proceed to define the two callback functions. 12:14.010 --> 12:18.090 So the one that will contain the logic for the orientation conversion. 12:18.770 --> 12:24.800 Let's start with the logic for the conversion between Euler angles into a quaternion. 12:24.920 --> 12:31.400 So in the Euler to quaternion callback function, let's first print a message in the terminal. 12:32.210 --> 12:46.730 So with the get logger function, let's print an informative message that says requested to convert 12:47.570 --> 12:53.510 to Euler angles, and then let's print the value of the Euler angle that was requested. 12:53.540 --> 12:56.510 So overall this is a floating number. 12:56.550 --> 12:58.670 Then pitch. 13:00.800 --> 13:01.670 Then you. 13:05.730 --> 13:08.670 And we want to convert this one into a. 13:10.840 --> 13:11.290 Quaternion. 13:12.080 --> 13:19.340 And so let's print then the value of the angles roll pitch and yaw that we want to convert. 13:19.340 --> 13:24.010 And so we can access to these values within the request message. 13:24.020 --> 13:25.880 So let's take the roll. 13:27.080 --> 13:31.460 Then still from the request message, let's take the pitch. 13:33.740 --> 13:37.700 And the you to perform the actual conversion. 13:37.730 --> 13:43.220 We can use a package available in Ros two called TF transformations. 13:43.700 --> 13:51.230 However, we first need to install it in our system and so to do so let's open a new terminal and let's 13:51.230 --> 14:00.170 execute the command sudo apt get install ros followed by the Ros two version that you are using. 14:00.170 --> 14:05.930 So in my case it is humble followed by the name of the package that is the TF. 14:08.360 --> 14:12.920 Train transformations. 14:13.130 --> 14:14.870 So let's press enter. 14:21.180 --> 14:26.850 And this is installing the transformation module for Roscoe Ambel. 14:27.330 --> 14:33.090 Then let's also install another Python library that is called transforms 3D. 14:33.480 --> 14:35.730 And we can install this one with pip. 14:35.730 --> 14:40.980 So the Python package manager with sudo pip three. 14:41.010 --> 14:45.450 Since we are using Python three and let's install. 14:47.840 --> 14:49.220 Transforms. 14:50.650 --> 14:51.090 3D. 14:52.210 --> 14:55.380 Now we can go back to the angles converter node. 14:55.390 --> 14:57.250 So let's close the terminal. 14:57.430 --> 15:02.290 And now we can start using these modules that we have just installed. 15:02.530 --> 15:15.820 So from the TF transformations module let's import the quaternion from Euler function. 15:15.820 --> 15:17.440 And let's use this function. 15:17.440 --> 15:22.270 So the quaternion from Euler within the Euler to quaternion callback. 15:22.270 --> 15:23.590 So here. 15:24.190 --> 15:26.740 So let's call this function. 15:26.740 --> 15:30.910 And this function takes as input the three Euler angles. 15:30.910 --> 15:34.420 So the three variables that we received in the request message. 15:34.420 --> 15:42.170 So request roll request pitch and request your. 15:43.650 --> 15:50.610 This is your story, and it returns the four coefficient of the quaternion, which we can store directly 15:50.610 --> 15:55.500 in the x, y, z and w variables of the response message. 15:55.650 --> 15:59.700 So let's store this one within the response message. 15:59.700 --> 16:05.130 So let's store the x variable then the y variable. 16:06.260 --> 16:12.500 Then the z variable and then the w, so the four coefficients of the quaternion. 16:12.590 --> 16:16.970 Let's finally print also another message in the console in the terminal. 16:20.420 --> 16:32.360 So an informative message that says corresponding quaternion and then the four values so x. 16:35.020 --> 16:35.800 Then why? 16:40.220 --> 16:41.030 Then it. 16:44.310 --> 16:45.710 And then we have W. 16:48.200 --> 16:54.200 And let's finally return also the response message to the client that requested the execution of this 16:54.200 --> 16:54.680 service. 16:54.680 --> 16:58.160 So let's return the response. 16:58.370 --> 17:01.160 Let's continue with the second callback function. 17:01.160 --> 17:03.860 So the quaternion to Euler callbacks. 17:04.070 --> 17:08.600 And here again let's start by printing an informative message in the terminal. 17:10.090 --> 17:22.780 So get longer and let's print an informative message that says requested to convert and then quaternion 17:22.780 --> 17:25.630 followed by the four coefficient of the quaternion. 17:25.900 --> 17:29.710 And so let's print the x the y. 17:32.260 --> 17:33.190 The z. 17:35.300 --> 17:37.730 And the W of the quaternion. 17:38.300 --> 17:42.590 Here we forgot also at the end of the string that we need to print. 17:43.860 --> 17:44.520 All of these. 17:44.520 --> 17:46.830 So we need to print all of these variables. 17:48.510 --> 17:49.110 Okay. 17:49.110 --> 17:51.810 And we need to do the same also here. 17:52.020 --> 17:54.870 So here we need also to print the four coefficient. 17:54.870 --> 18:00.030 But as this is the callback function for the quaternion to Euler service. 18:00.060 --> 18:04.590 Now the four coefficient of the quaternion are in the request message. 18:04.680 --> 18:10.410 So here let's print the four coefficients of the quaternion that are in the request message. 18:10.680 --> 18:19.320 And so let's print the x component, then the y component, then the z component. 18:19.530 --> 18:22.310 And finally also the w component. 18:22.320 --> 18:29.010 And now in order to perform the conversion from a quaternion to Euler angles, we can use another function 18:29.010 --> 18:32.100 still from the tf transformations library. 18:32.100 --> 18:36.450 And this one is called Euler from quaternion. 18:36.450 --> 18:43.230 So let's import this function and let's use it here within the quaternion to Euler callback function. 18:43.230 --> 18:50.160 So let's use the Euler from quaternion function and this one receives as input a vector with the four 18:50.160 --> 18:51.750 components of the quaternion. 18:51.750 --> 18:52.140 And. 18:52.140 --> 18:56.940 So let's pass a vector and the four component are defined here. 18:56.940 --> 18:59.940 So those that are in the request message. 18:59.940 --> 19:06.630 So we can paste it here also in the list that we are passing to the Euler from quaternion function. 19:06.750 --> 19:11.310 And also this function returns the corresponding three Euler angles. 19:11.310 --> 19:17.790 So we can store the three Euler angles that this function returns directly in the response message. 19:17.940 --> 19:30.750 So let's store the role in the response role and then also the pitch and also the yo. 19:30.960 --> 19:37.620 So we are storing the output of this function directly within the response message that the service 19:37.620 --> 19:39.240 server will return. 19:39.450 --> 19:43.050 And now let's print another informative message in the terminal. 19:43.050 --> 19:55.260 So actually we can paste this one here in order to print the corresponding user angles. 19:55.260 --> 19:57.090 And so we want to print the role. 19:59.260 --> 20:03.990 The pitch and also the yo. 20:04.000 --> 20:06.850 So the converted values. 20:07.090 --> 20:12.820 And so now we can print the converted values that we have stored here in the response message. 20:12.820 --> 20:15.910 So let's print those three values. 20:17.320 --> 20:20.020 And finally with this we can return. 20:20.620 --> 20:23.020 So let's return the result. 20:23.050 --> 20:25.720 The response of the service server. 20:26.050 --> 20:30.460 With this we have completed the implementation of the angle converter node. 20:30.460 --> 20:34.810 And now we can proceed to use its functionalities within the main function. 20:34.810 --> 20:37.180 So here that we have already defined. 20:37.330 --> 20:41.470 Here we only need to change the name of the class that we want to instantiate. 20:41.470 --> 20:44.720 That is called angles converter. 20:44.740 --> 20:51.910 Let's also change the name here of the variable into angles converter. 20:51.940 --> 20:53.740 Let's make it spin. 20:54.190 --> 20:58.630 And also let's destroy the node whenever we press Ctrl c. 20:59.380 --> 21:05.620 Now let's save this file and we need to inform the compiler about the existence of this Python node 21:05.620 --> 21:09.880 so that it can be compiled and converted into an executable. 21:10.240 --> 21:17.380 Since we are using CMake as a build type for the Arduino utils package, we need to follow a slightly 21:17.380 --> 21:24.910 different approach for the installation of a node using the Cmakelists.txt file, where we can install 21:24.910 --> 21:27.700 both Python and C plus plus node. 21:27.910 --> 21:34.780 So let's open this file, and let's start by declaring the dependencies that we used in our Python node. 21:34.810 --> 21:39.190 So here where there is the find package instruction. 21:39.190 --> 21:42.190 Let's copy this instruction and let's paste it. 21:42.340 --> 21:48.070 And we are using the RTL Pi library for our Python node. 21:48.160 --> 21:50.920 Also let's paste it again. 21:50.920 --> 21:59.830 And we are using also the Arduino but messages package from which we use the interfaces to quaternion 21:59.830 --> 22:06.820 and quaternion to Euler to talk with the service servers, and then to declare that the Arduino utils 22:06.820 --> 22:09.400 package contains some Python nodes. 22:09.550 --> 22:10.720 We need to use. 22:10.720 --> 22:17.410 So here after the find package we need to insert an amend python. 22:20.080 --> 22:24.070 Install package instruction. 22:24.070 --> 22:30.460 And so we use the name of the package which contains these Python nodes, which is also contained in 22:30.460 --> 22:31.630 the variable. 22:33.430 --> 22:35.980 Project name. 22:36.640 --> 22:39.710 And now we can finally install our Python node. 22:39.730 --> 22:46.710 So after the Python install package let's use the install instruction. 22:46.750 --> 22:48.670 And so let's install a new program. 22:50.530 --> 22:57.400 So programs and here are the script that we want to install is in the Arduino utils sub folder. 22:57.400 --> 23:02.200 So is in this folder that has the same name as the package itself. 23:02.200 --> 23:08.470 And so let's still using the variable project name. 23:08.560 --> 23:13.690 And then we need to declare the name of the script that is the angle. 23:16.550 --> 23:17.630 Conversion. 23:18.700 --> 23:21.760 Dot pi and we want to install this one. 23:21.760 --> 23:28.000 So in the destination of the executable will be the lib folder. 23:28.000 --> 23:31.300 And inside the Arduino board utils sub folder. 23:31.300 --> 23:39.400 So still as this has the same name of the package, let's use the variable project name. 23:40.250 --> 23:44.180 So with this also the file cmake list is done. 23:44.570 --> 23:47.460 Then as we are installing a Python node. 23:47.480 --> 23:48.620 So this one. 23:48.620 --> 23:53.030 Let's also insert the dependency from the build type. 23:53.570 --> 23:56.750 Here I meant cmake python. 23:57.110 --> 24:01.220 So let's add the cmake python. 24:02.180 --> 24:04.580 In order to build Python nodes. 24:05.430 --> 24:09.790 And with this our cmakelists.txt file is ready. 24:09.810 --> 24:13.020 So we have defined all the dependencies. 24:13.020 --> 24:18.120 And also we have defined how the build tool should build and install our Python node. 24:18.490 --> 24:24.960 And so now we can move on and declare also the dependencies that we used in the package dot XML file. 24:25.140 --> 24:28.320 So here let's add a dependency. 24:28.320 --> 24:36.270 So another build tool dependency from the CMake Python that we are going to need to build our Python 24:36.270 --> 24:36.660 node. 24:36.660 --> 24:42.270 And then let's add a dependency from the Rql py library. 24:42.840 --> 24:50.820 Then let's also add another dependency on the Arduino bot messages. 24:51.540 --> 24:57.690 With this we have completed the creation of our node, and so we have instructed the compiler on how 24:57.690 --> 24:59.550 it should make it an executable. 24:59.550 --> 25:03.270 And also we have defined the dependencies that this node needs. 25:03.390 --> 25:07.920 Now we can finally build our workspace and see how this node works. 25:08.070 --> 25:09.810 So let's open a new terminal. 25:10.770 --> 25:16.380 Let's go into the workspace and let's build it with the command called build. 25:16.590 --> 25:18.570 So the build is successful. 25:18.600 --> 25:21.660 This means that we have now an executable for our nodes. 25:21.660 --> 25:23.160 And so let's start them. 25:24.180 --> 25:26.970 So let's open a new window of the terminal here. 25:26.970 --> 25:28.530 Let's search the workspace. 25:28.650 --> 25:32.610 So the file setup dot bash that is in the install folder. 25:32.610 --> 25:35.190 And let's run the node for the angle conversion. 25:35.190 --> 25:45.540 So Ross to run and from the Arduino boot utils package let's start the angle conversion dot pi node. 25:45.570 --> 25:47.580 So let's press enter. 25:47.580 --> 25:53.640 And upon the node start up we can already see that it informs us that the angle conversion services 25:53.640 --> 25:59.310 are correctly running, and so they are ready to process new conversion requests. 25:59.520 --> 26:02.760 We can verify also this by opening a new terminal. 26:02.760 --> 26:09.060 And so if we launch the Command Ross queue service list. 26:09.060 --> 26:14.070 So we get a list of all the services that are currently available in Ross queue. 26:14.070 --> 26:20.550 And apart from the one that were automatically created by the initialization of the Ross to node, we 26:20.550 --> 26:26.220 can see that there are the two services that we called earlier to quaternion and also quaternion to 26:26.250 --> 26:26.730 Euler. 26:27.480 --> 26:30.600 Let's try to send a request to these services. 26:30.600 --> 26:36.360 And to do so we need to source the workspace, which contains the definition of the message interface 26:36.360 --> 26:38.940 that we need to use in order to contact the server. 26:38.940 --> 26:41.400 So in order to send a request to this server. 26:41.670 --> 26:46.440 And so let's use the command Ros2 service call. 26:46.710 --> 26:51.660 And let's for example call the user to quaternion. 26:51.690 --> 26:58.770 We can see that pressing tab twice we get the autocompletion of Ros two that says that this service. 26:58.770 --> 27:03.570 So the user to quaternion requests an interface of this type. 27:03.570 --> 27:09.690 So an interface of type user to quaternion as defined in the Arduino bot messages. 27:09.690 --> 27:11.520 So let's use this interface. 27:11.520 --> 27:13.920 Then let's press again tab twice. 27:13.950 --> 27:15.750 Let's use the double quotes. 27:15.750 --> 27:17.580 Then again let's press tab. 27:17.580 --> 27:20.970 And let's type role and then tab again. 27:20.970 --> 27:24.420 And now we can see that the message is autocompleted. 27:24.570 --> 27:27.420 So now we can send our request. 27:27.420 --> 27:33.540 So basically we can ask the service server to convert a certain Euler angles. 27:33.540 --> 27:36.510 So roll pitch into a quaternion. 27:36.810 --> 27:45.570 For example let's set the roll angle so this 1 to -0.5. 27:45.690 --> 27:49.230 And then let's set the pitch to zero. 27:49.230 --> 27:53.880 And for example let's set this 1 to 1.5. 27:54.510 --> 27:56.340 Let's press enter. 27:56.910 --> 28:00.720 And here we can see that there is an error in our Python script. 28:00.990 --> 28:09.300 So if we go back to the angle conversion actually here we see that we are missing a percentage sign. 28:10.060 --> 28:11.560 And we don't need the comb. 28:11.590 --> 28:12.220 Actually. 28:13.130 --> 28:18.260 Okay, so now we can go back and build again our workspace. 28:19.060 --> 28:20.590 Let's launch again a word note. 28:22.520 --> 28:25.430 And let's send again the request message. 28:25.430 --> 28:28.030 And now the request is successful. 28:28.040 --> 28:35.320 And so we can see that actually the service server response with the corresponding quaternion coefficients. 28:35.330 --> 28:41.540 So these ones that are the result of the conversion between these angles. 28:41.540 --> 28:45.050 So these roll pitch and the into a quaternion. 28:45.050 --> 28:51.260 And also we can see that the client that is this one is receiving the correct response. 28:51.260 --> 28:54.980 So is receiving the four coefficients of the quaternion. 28:55.710 --> 28:58.330 Now let's try to call the second service. 28:58.350 --> 29:02.580 So with the Ros two service call. 29:02.880 --> 29:05.880 And now let's call the quaternion to Euler. 29:06.450 --> 29:13.800 Again we can press tab twice to see that this service is using the quaternion two user interface as 29:13.800 --> 29:15.780 defined in the Arduino board messages. 29:16.440 --> 29:18.060 So let's use this interface. 29:18.060 --> 29:20.010 Then let's use the double quotes. 29:20.040 --> 29:21.600 Let's press tab twice. 29:21.600 --> 29:24.750 Then let's type x and again tab. 29:24.870 --> 29:32.270 And now we get an empty prototype of the request message that this quaternion to Euler service is accepting. 29:32.310 --> 29:37.800 And so now we need to set the quaternion that we want to convert into Euler angles. 29:38.010 --> 29:41.550 For example let's ask to convert the unit quaternion. 29:41.550 --> 29:48.420 So basically the quaternion that has all the components set to zero except for the last one which corresponds 29:48.420 --> 29:49.270 to one. 29:49.290 --> 29:56.610 So let's press enter and we can see that here we have the corresponding Euler angles that corresponds 29:56.610 --> 29:59.580 to this unitary quaternion rotation. 29:59.580 --> 30:05.040 And so this basically indicates that both the service servers are correctly running.