WEBVTT 00:00.080 --> 00:03.620 We are now in step number five for this final project. 00:03.620 --> 00:08.960 And while the project is actually working, you just saw that the turtle is actually catching all the 00:08.960 --> 00:10.190 other turtles. 00:10.190 --> 00:13.430 Now we are going to improve that project and in this step. 00:13.430 --> 00:14.840 So it's not going to be that long. 00:14.840 --> 00:20.990 We're going to choose to target the closest turtle instead of the first turtle in the list. 00:21.020 --> 00:21.320 Okay. 00:21.350 --> 00:28.670 And first I'm going to show you with the I can increase the frequency here in the turtle spawner. 00:28.700 --> 00:35.030 Let's say instead of two seconds between each turtle I'm going to put 0.5 okay. 00:35.060 --> 00:37.250 So I'm going to spawn a lot more turtles. 00:37.250 --> 00:41.330 And let's see what's going to be the behavior of the master turtle. 00:42.470 --> 00:48.770 So now I start the turtle sim node I start the controller again. 00:49.070 --> 00:53.090 Let's put turtle here and I start the spawner. 00:53.660 --> 00:57.230 So it's going to spawn turtle quite fast. 00:57.230 --> 01:05.510 And well, as you can see, the turtle is just going through all of the other target turtles, but in 01:05.510 --> 01:07.380 the order in which they appeared. 01:07.620 --> 01:09.420 Which is the order of the list. 01:09.630 --> 01:10.050 All right. 01:10.080 --> 01:17.280 We could improve that a lot by saying that we just try to go to the nearest turtle instead of the first 01:17.280 --> 01:18.450 turtle in the list. 01:18.510 --> 01:19.290 All right. 01:19.650 --> 01:22.020 So let's do that in the code. 01:22.650 --> 01:24.510 And where do we do this. 01:24.540 --> 01:27.000 Actually there is nothing to do in the turtle spawner. 01:27.030 --> 01:27.330 Okay. 01:27.360 --> 01:34.170 This node is just spawning turtles and killing turtles and also publishing the current list of alive 01:34.200 --> 01:34.950 turtles. 01:34.950 --> 01:38.670 So this is in the turtle controller. 01:38.670 --> 01:46.170 When we receive the list of alive turtles here, you can see we decide to chase the first one. 01:46.170 --> 01:52.350 But what we could do instead is to actually compute the distance for each turtle and find the nearest 01:52.350 --> 01:54.390 one, and just go to the nearest one. 01:54.390 --> 01:56.550 And actually here I'm going to give the choice. 01:56.550 --> 02:07.170 I'm going to create a variable called self dot catch closest turtle first. 02:09.090 --> 02:10.980 By default it's going to be true. 02:12.120 --> 02:23.440 And here I'm going to say if self catch closes total first we do something I'm going to put pass and 02:23.440 --> 02:29.290 then else we go to the first one okay. 02:29.320 --> 02:35.860 And then we can maybe put that as a parameter so that the user, when we actually run that node we can 02:35.860 --> 02:41.500 choose do we want to catch the closest total first or just follow the order of the list. 02:41.530 --> 02:41.830 All right. 02:41.860 --> 02:43.240 So I keep both options. 02:43.240 --> 02:48.280 Now to find the closest total we're going to receive a list of turtles. 02:48.280 --> 02:49.840 We just go through the list. 02:49.870 --> 02:55.960 We compute the distance for each turtle compared to where we are right now using the current pose. 02:55.960 --> 03:00.850 And we just say that the turtle to catch is the one with the smallest distance. 03:01.180 --> 03:10.990 So here as a helper variables, I'm just going to create the closest turtle initialized to none. 03:10.990 --> 03:18.790 And then I'm going to create closest turtle distance. 03:20.270 --> 03:23.690 And then I do for turtle in. 03:24.740 --> 03:27.020 So message turtles. 03:27.050 --> 03:28.370 Okay, that's the list. 03:28.880 --> 03:29.690 And we are in this. 03:29.720 --> 03:32.450 If so, we know that we have at least one element. 03:32.450 --> 03:34.640 So for each turtle what do I do. 03:34.670 --> 03:36.710 I will compute the distance. 03:36.740 --> 03:49.790 To compute the distance I need to first get the distance x which is well the turtle we get here x minus 03:49.790 --> 03:54.020 self dot pose dot x. 03:54.140 --> 03:54.740 Okay. 03:54.770 --> 03:56.840 It's the same thing we do here basically. 03:56.840 --> 04:06.290 And then distance y is going to be turtle dot y minus self pose y. 04:06.410 --> 04:07.520 And we can do. 04:07.550 --> 04:11.570 Actually I'm just going to take that line because it's going to be the exact same. 04:11.600 --> 04:20.780 The distance is the square root of the distance x multiplied by itself plus the distance y multiplied 04:20.780 --> 04:22.040 by itself. 04:22.610 --> 04:30.750 So with this we have the distance between the turtle so that turtle in the array and our current pose. 04:30.750 --> 04:33.090 So the pose of the master turtle. 04:33.120 --> 04:33.720 Then I'm going to do. 04:33.750 --> 04:38.940 If the closest turtle is well is none. 04:39.090 --> 04:51.300 If it's not initialized or if the distance is lower than the closest turtle distance, I just say that 04:51.300 --> 05:01.800 the closest turtle is the current one, so the turtle and the closest turtle distance is the current 05:01.800 --> 05:03.450 distance we have computed. 05:03.480 --> 05:03.870 All right. 05:03.870 --> 05:07.200 So the first time we go to the if closest turtle is none. 05:07.200 --> 05:11.220 So it's going to basically save that turtle as the closest turtle. 05:11.220 --> 05:13.620 And we also save the distance. 05:13.620 --> 05:16.980 You see we saved the distance as the closest turtle distance. 05:16.980 --> 05:20.100 And then for the next ones we just compute the new distance. 05:20.100 --> 05:25.230 And if it's shorter we save that turtle as the new closest turtle. 05:25.230 --> 05:27.780 And we also keep the distance for the next time. 05:27.780 --> 05:34.960 So basically after we are done with this for loop, we know that the closest total variable here contains 05:34.960 --> 05:36.850 the closest total. 05:36.850 --> 05:43.630 So we can do self dot total to catch is equal to closest total. 05:43.690 --> 05:44.290 All right. 05:44.290 --> 05:45.040 And that's it. 05:45.040 --> 05:50.290 Because then we just decide to not follow the first one in the list. 05:50.320 --> 05:53.800 We just decide to choose whatever is the closest. 05:54.220 --> 05:55.780 Then we're going to chase it. 05:55.780 --> 06:03.130 And at the end we just call this service catch total is going to remove that total and then send the 06:03.130 --> 06:06.730 new list with just the turtles that are alive. 06:06.730 --> 06:11.620 And one thing that's going to be interesting, and we're going to be able to see that when we test, 06:11.650 --> 06:18.130 is that whenever you receive a new list of turtles, this is going to be computed again. 06:18.130 --> 06:25.390 So if let's say the turtle is the master turtle is currently chasing one turtle, but then one other 06:25.390 --> 06:29.050 turtle is found very close to the master turtle. 06:29.080 --> 06:33.550 Then because we receive a new list, we compute the distances with all turtles. 06:33.550 --> 06:40.790 If that new turtle is closest than the current one we are chasing, we might actually change the target. 06:40.880 --> 06:41.450 Okay. 06:41.480 --> 06:43.880 So let's actually see that with an example. 06:44.090 --> 06:50.510 So now I can start I'm going to change actually the frequency. 06:50.540 --> 06:53.990 Well instead of 0.5 I'm going to use 0.8. 06:54.050 --> 06:57.020 Not to spawn turtles two too fast. 06:58.250 --> 07:00.920 So let's start the turtle sim node. 07:01.910 --> 07:03.650 Let's start the controller. 07:03.650 --> 07:05.570 And let's start the spawner. 07:05.570 --> 07:06.800 And let's see what happens. 07:08.690 --> 07:10.190 So we chased that one. 07:10.460 --> 07:11.210 Okay. 07:11.690 --> 07:12.560 Okay. 07:13.610 --> 07:15.530 And let's wait until. 07:15.920 --> 07:18.680 So maybe the case is going to be soon or not. 07:19.280 --> 07:24.380 But maybe at some point you see okay now we were going to that turtle here. 07:24.380 --> 07:26.450 But then this one spawned. 07:26.450 --> 07:31.760 So the turtle just changed its trajectory to catch that one instead. 07:31.790 --> 07:32.030 Okay. 07:32.060 --> 07:33.410 That's what I was talking about. 07:33.410 --> 07:35.870 And now you can see it's much more smooth. 07:35.900 --> 07:36.110 Okay. 07:36.140 --> 07:37.100 And it makes more sense. 07:37.100 --> 07:38.540 We go to the nearest one. 07:38.720 --> 07:39.020 Okay. 07:39.050 --> 07:40.820 We don't go to the first one on the list. 07:40.850 --> 07:42.230 We go to the nearest one.