# Orbit Follower

Orbit location of interest using UAV

**Library:**UAV Toolbox / Algorithms

## Description

The Orbit Follower block generates course and yaw controls for following a
circular orbit around a location of interest based on the unmanned aerial vehicle's (UAV's)
current pose. Select a **UAV type** of fixed-wing or multirotor UAVs. You can
specify any orbit center location, orbit radius, and turn direction. A lookahead distance,
**LookaheadDistance**, is used for tuning the path tracking and generating
the **LookaheadPoint** output.

## Ports

### Input

`Pose`

— Current UAV pose

`[x y z course]`

vector

Current UAV pose, specified as an `[x y z course]`

vector.
`[x y z]`

is the UAV's position in NED coordinates
(north-east-down) specified in meters. `course`

is the angle between
ground velocity and north direction in radians per second.

**Example: **
`[1,1,-10,pi/4]`

**Data Types: **`single`

| `double`

`Center`

— Center of orbit

`[x y z]`

vector

Center of orbit, specified as an `[x y z]`

vector. ```
[x y
z]
```

is the orbit center position in NED coordinates (north-east-down)
specified in meters.

**Example: **
`[5,5,-10]`

**Data Types: **`single`

| `double`

`Radius`

— Radius of orbit

positive scalar

Radius of orbit, specified as a positive scalar in meters.

**Example: **
`5`

**Data Types: **`single`

| `double`

`TurnDirection`

— Direction of orbit

scalar

Direction of orbit, specified as a scalar. Positive values indicate a clockwise
turn as viewed from above. Negative values indicate a counter-clockwise turn. A value
of `0`

automatically determines the value based on the input to
**Pose**.

**Example: **
`-1`

**Data Types: **`single`

| `double`

`LookaheadDistance`

— Lookahead distance for tracking orbit

positive scalar

Lookahead distance for tracking the orbit, specified as a positive scalar. Tuning this value helps adjust how tightly the UAV follows the orbit circle. Smaller values improve tracking, but can lead to oscillations in the path.

**Example: **
`2`

**Data Types: **`single`

| `double`

`ResetNumTurns`

— Reset for counting turns

numeric signal

Reset for counting turns, specified as a numeric signal. Any rising signal
triggers a reset of the **NumTurns** output.

**Example: **
`2`

#### Dependencies

To enable this input, select `rising`

for **External
reset**.

**Data Types: **`single`

| `double`

### Output

`LookaheadPoint`

— Lookahead point on path

`[x y z]`

position vector

Lookahead point on path, returned as an `[x y z]`

position vector
in meters.

**Data Types: **`double`

`DesiredCourse`

— Desired course

numeric scalar

Desired course, returned as numeric scalar in radians in the range of
`[-pi, pi]`

. The UAV course is the angle of direction of the
velocity vector relative to north measured in radians. For fixed-wing type UAV, the
values of desired course and desired yaw are equal.

**Data Types: **`double`

`DesiredYaw`

— Desired yaw

numeric scalar

Desired yaw, returned as numeric scalar in radians in the range of ```
[-pi,
pi]
```

. The UAV yaw is the forward direction of the UAV (regardless of the
velocity vector) relative to north measured in radians. For fixed-wing type UAV, the
values of desired course and desired yaw are equal.

**Data Types: **`double`

`OrbitRadiusFlag`

— Orbit radius flag

`0`

(default) | `1`

Orbit radius flag, returned as `0`

or `1`

.
`0`

indicates orbit radius is not saturated, `1`

indicates orbit radius is saturated to minimum orbit radius value specified.

**Data Types: **`uint8`

`LookaheadDistFlag`

— Lookahead distance flag

`0`

(default) | `1`

Lookahead distance flag, returned as `0`

or `1`

.
`0`

indicates lookahead distance is not saturated,
`1`

indicates lookahead distance is saturated to minimum lookahead
distance value specified.

**Data Types: **`uint8`

`CrossTrackError`

— Cross track error from UAV position to path

positive numeric scalar

Cross track error from UAV position to path, returned as a positive numeric scalar in meters. The error measures the perpendicular distance from the UAV position to the closest point on the path.

#### Dependencies

This port is only visible if **Show CrossTrackError output
port** is checked.

**Data Types: **`double`

`NumTurns`

— Number of times the UAV has completed the orbit

numeric scalar

Number of times the UAV has completed the orbit, returned as a numeric scalar. As
the UAV circles the center point, this value increases or decreases based on the
specified **Turn Direction**. Decimal values indicate partial
completion of a circle. If the UAV cross track error exceeds the lookahead distance,
the number of turns is not updated.

**NumTurns** is reset whenever **Center**,
**Radius**, or **TurnDirection** are changed. You
can also use the **ResetNumTurns** input.

#### Dependencies

This port is only visible if **Show NumTurns output port** is
checked.

## Parameters

`UAV type`

— Type of UAV

`fixed-wing`

(default) | `multirotor`

Type of UAV, specified as either `fixed-wing`

or
`multirotor`

.

This parameter is non-tunable.

`Minimum orbit radius (m)`

— Minimum orbit radius

`1`

(default) | positive numeric scalar

Minimum orbit radius, specified as a positive numeric scalar in meters.

When input to the orbit **Radius** port is less than the minimum
orbit radius, the **OrbitRadiusFlag** is returned as
`1`

and the orbit radius value is specified as the value of minimum
orbit radius.

This parameter is non-tunable.

`Minimum lookahead distance (m)`

— Minimum lookahead distance

`0.1`

(default) | positive numeric scalar

Minimum lookahead distance, specified as a positive numeric scalar in meters.

When input to the **LookaheadDistance** port is less than the
minimum lookahead distance, the **LookaheadDistFlag** is returned as
`1`

and the lookahead distance value is specified as the value of
minimum lookahead distance.

This parameter is non-tunable.

`External reset`

— Reset trigger source

`none`

(default) | `rising`

Select `rising`

to enable the **ResetNumTurns**
block input.

This parameter is non-tunable.

`Show CrossTrackError output port`

— Output cross track error

`off`

(default) | `on`

Output cross track error from the **CrossTrackError** port.

This parameter is non-tunable.

`Show NumTurns output port`

— Output UAV waypoint status

`off`

(default) | `on`

Output UAV waypoint status from the **Status** port.

This parameter is non-tunable.

## Extended Capabilities

### C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

**Introduced in R2019a**

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