# getTrackPositions

Returns updated track positions and position covariance matrix

## 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 = 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 = 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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Object tracks, specified as an array of objectTrack objects or an array of structures containing sufficient information to obtain the track position information. At a minimum, these structures must contain a State column vector field and a positive-definite StateCovariance matrix field. For a sample track structure, see toStruct.

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.

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

## Version History

Introduced in R2018b