Documentation

# environment

Environmental inputs for UAV

## Syntax

``envStruct = environment(uavGuidanceModel)``

## Description

example

``` NoteThis function requires you to install the UAV Library for Robotics System Toolbox™. To install add-ons, use `roboticsAddons` and select the desired add-on. `envStruct = environment(uavGuidanceModel)` returns a structure that captures all the relevant environmental variables for the specified UAV guidance model. Use this function to ensure you have the proper fields for your environmental parameters. Use the environmental inputs as an input to the `derivative` function to get the state time-derivative of the UAV.```

## Examples

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This example shows how to use the `multirotor` guidance model to simulate the change in state of a UAV due to a command input.

Note: To use UAV algorithms, you must install the UAV Library for Robotics System Toolbox®. To install, use `roboticsAddons``.`

Create the multirotor guidance model.

`model = multirotor;`

Create a state structure. Specify the location in world coordinates.

```s = state(model); s(1:3) = [3;2;1];```

Specify a control command, `u`, that specified the roll and thrust of the multirotor.

```u = control(model); u.Roll = pi/12; u.Thrust = 1;```

Create a default environment without wind.

`e = environment(model);`

Compute the time derivative of the state given the current state, control command, and environment.

`sdot = derivative(model,s,u,e);`

Simulate the UAV state using `ode45` integration. The `y` field outputs the fixed-wing UAV states as a 13-by-n matrix.

```simOut = ode45(@(~,x)derivative(model,x,u,e), [0 3], s); size(simOut.y)```
```ans = 1×2 13 3536 ```

Plot the change in roll angle based on the simulation output. The roll angle (the X Euler angle) is the 9th row of the `simOut.y` output.

`plot(simOut.y(9,:))`

Plot the change in the Y and Z positions. With the specified thrust and roll angle, the multirotor should fly over and lose some altitude. A positive value for Z is expected as positive Z is down.

```figure plot(simOut.y(2,:)); hold on plot(simOut.y(3,:)); legend('Y-position','Z-position') hold off```

You can also plot the multirotor trajectory using `plotTransforms`. Create the translation and rotation vectors from the simulated state. Downsample (every 300th element) and transpose the `simOut` elements, and convert the Euler angles to quaternions. Specify the mesh as the `multirotor.stl` file and the positive Z-direction as `"down"`. The displayed view shows the UAV translating in the Y-direction and losing altitude.

```translations = simOut.y(1:3,1:300:end)'; % xyz position rotations = eul2quat(simOut.y(7:9,1:300:end)'); % ZYX Euler plotTransforms(translations,rotations,... 'MeshFilePath','multirotor.stl','InertialZDirection',"down") view([90.00 -0.60])```

This example shows how to use the `fixedwing` guidance model to simulate the change in state of a UAV due to a command input.

Note: To use UAV algorithms, you must install the UAV Library for Robotics System Toolbox®. To install, use `roboticsAddons``.`

Create the fixed-wing guidance model.

`model = fixedwing;`

Set the air speed of the vehicle by modifying the structure from the `state` function.

```s = state(model); s(4) = 5; % 10 m/s```

Specify a control command, `u`, that maintains the air speed and gives a roll angle of `pi/12`.

```u = control(model); u.RollAngle = pi/12; u.AirSpeed = 5;```

Create a default environment without wind.

`e = environment(model);`

Compute the time derivative of the state given the current state, control command, and environment.

`sdot = derivative(model,s,u,e);`

Simulate the UAV state using `ode45` integration. The `y` field outputs the fixed-wing UAV states based on this simulation.

```simOut = ode45(@(~,x)derivative(model,x,u,e), [0 50], s); size(simOut.y)```
```ans = 1×2 8 904 ```

Plot the change in roll angle based on the simulation output. The roll angle is the 7th row of the `simOut.y` output.

`plot(simOut.y(7,:))`

You can also plot the fixed-wing trajectory using `plotTransforms`. Create the translation and rotation vectors from the simulated state. Downsample (every 30th element) and transpose the `simOut` elements, and convert the Euler angles to quaternions. Specify the mesh as the `fixedwing.stl` file and the positive Z-direction as `"down"`. The displayed view shows the UAV making a constant turn based on the constant roll angle.

```downsample = 1:30:size(simOut.y,2); translations = simOut.y(1:3,downsample)'; % xyz-position rotations = eul2quat([simOut.y(5,downsample)',simOut.y(6,downsample)',simOut.y(7,downsample)']); % ZYX Euler plotTransforms(translations,rotations,... 'MeshFilePath','fixedwing.stl','InertialZDirection',"down") hold on plot3(simOut.y(1,:),-simOut.y(2,:),simOut.y(3,:),'--b') % full path xlim([-10.0 10.0]) ylim([-20.0 5.0]) zlim([-0.5 4.00]) view([-45 90]) hold off```

## Input Arguments

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UAV guidance model, specified as a `fixedwing` or `multirotor` object.

## Output Arguments

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Environmental input parameters, returned as a structure.

For fixed-wing UAVs, the fields of the structure are `WindNorth`, `WindEast`,`WindDown`, and `Gravity`. Wind speeds are in meters per second and negative speeds point in the opposite direction. `Gravity` is in meters per second squared (default `9.81`).

For multirotor UAVs, the only element of the structure is `Gravity` (default `9.81`) in meters per second.

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