# getTrackPositions

Returns updated track positions and position covariance matrix

## Syntax

``position = getTrackPositions(tracks,positionSelector)``
``````[position,positionCovariances] = getTrackPositions(tracks,positionSelector)``````

## Description

example

````position = getTrackPositions(tracks,positionSelector)` returns a matrix of track positions. Each row contains the position of a tracked object.```

example

``````[position,positionCovariances] = getTrackPositions(tracks,positionSelector)``` returns a matrix of track positions.```

## Examples

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Create an extended Kalman filter tracker for 3-D constant-acceleration motion.

`tracker = trackerTOMHT('FilterInitializationFcn',@initcaekf);`

Update the tracker with a single detection and get the tracks output.

```detection = objectDetection(0,[10;-20;4],'ObjectClassID',3); tracks = step(tracker,detection,0)```
```tracks = objectTrack with properties: TrackID: 1 BranchID: 1 SourceIndex: 0 UpdateTime: 0 Age: 1 State: [9x1 double] StateCovariance: [9x9 double] StateParameters: [1x1 struct] ObjectClassID: 3 TrackLogic: 'Score' TrackLogicState: [13.7102 13.7102] IsConfirmed: 1 IsCoasted: 0 IsSelfReported: 1 ObjectAttributes: [1x1 struct] ```

Obtain the position vector from the track state.

```positionSelector = [1 0 0 0 0 0 0 0 0; 0 0 0 1 0 0 0 0 0; 0 0 0 0 0 0 1 0 0]; position = getTrackPositions(tracks, positionSelector)```
```position = 1×3 10.0000 -20.0000 4.0000 ```

Create an extended Kalman filter tracker for 3-D constant-velocity motion.

`tracker = trackerTOMHT('FilterInitializationFcn',@initcvekf);`

Update the tracker with a single detection and get the tracks output.

```detection = objectDetection(0,[10;3;-7],'ObjectClassID',3); tracks = step(tracker,detection,0)```
```tracks = objectTrack with properties: TrackID: 1 BranchID: 1 SourceIndex: 0 UpdateTime: 0 Age: 1 State: [6x1 double] StateCovariance: [6x6 double] StateParameters: [1x1 struct] ObjectClassID: 3 TrackLogic: 'Score' TrackLogicState: [13.7102 13.7102] IsConfirmed: 1 IsCoasted: 0 IsSelfReported: 1 ObjectAttributes: [1x1 struct] ```

Obtain the position vector and position covariance for that track

```positionSelector = [1 0 0 0 0 0; 0 0 1 0 0 0; 0 0 0 0 1 0]; [position,positionCovariance] = getTrackPositions(tracks,positionSelector)```
```position = 1×3 10.0000 3.0000 -7.0000 ```
```positionCovariance = 3×3 1.0000 -0.0000 0 -0.0000 1.0000 -0.0000 0 -0.0000 1.0000 ```

## Input Arguments

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Tracked object, specified as a `struct` array. A track `struct` array is an array of MATLAB® `struct` types containing sufficient information to obtain the track position vector and, optionally, the position covariance matrix. At a minimum, the `struct` must contain a `State` column vector field and a positive-definite `StateCovariance` matrix field. For an example of a track `struct` used by Sensor Fusion and Tracking Toolbox™, examine the output argument, `tracks`, returned by the `step` object function of `trackerGNN`.

Position selector, specified as a D-by-N real-valued matrix of ones and zeros. D is the number of dimensions of the tracker. N is the size of the state vector. Using this matrix, the function extracts track positions from the state vector. Multiply the state vector by position selector matrix returns positions. The same selector is applied to all object tracks.

## Output Arguments

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Positions of tracked objects at last update time, returned as a real-valued M-by-D matrix. D represents the number of position elements. M represents the number of tracks.

Position covariance matrices of tracked objects, returned as a real-valued D-by-D-M array. D represents the number of position elements. M represents the number of tracks. Each D-by-D submatrix is a position covariance matrix for a track.

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### Position Selector for 2-Dimensional Motion

Show the position selection matrix for two-dimensional motion when the state consists of the position and velocity.

`$\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 0& 1& 0\end{array}\right]$`

### Position Selector for 3-Dimensional Motion

Show the position selection matrix for three-dimensional motion when the state consists of the position and velocity.

`$\left[\begin{array}{cccccc}1& 0& 0& 0& 0& 0\\ 0& 0& 1& 0& 0& 0\\ 0& 0& 0& 0& 1& 0\end{array}\right]$`

### Position Selector for 3-Dimensional Motion with Acceleration

Show the position selection matrix for three-dimensional motion when the state consists of the position, velocity, and acceleration.

`$\left[\begin{array}{ccccccccc}1& 0& 0& 0& 0& 0& 0& 0& 0\\ 0& 0& 0& 1& 0& 0& 0& 0& 0\\ 0& 0& 0& 0& 0& 0& 1& 0& 0\end{array}\right]$`

## Extended Capabilities

### C/C++ Code GenerationGenerate C and C++ code using MATLAB® Coder™.

Introduced in R2018b