# mergeDetections

## Syntax

## Description

merges detections sharing the same cluster labels. By default, the function merges
detections in the same cluster using a Gaussian mixture merging algorithm. The function
assumes that all detections in the same cluster share the same `clusteredDetections`

= mergeDetections(`detections`

,`clusterIndex`

)`Time`

,
`SensorIndex`

, `ObjectClassID`

,
`MeasurementParameters`

, and `ObjectAttributes`

properties or fields.

specifies the function used to merge the detections in addition to the input arguments from
the previous syntax.`clusteredDetections`

= mergeDetections(___,MergingFcn=`mergeFcn`

)

## Examples

### Merge Detections to Generate Clustered Detections

Generate two clusters of detections with two false alarms.

rng(2021) % For repeatable results x1 = [5; 5; 0] + randn(3,4); % Four detections in cluster one x2 = [5; -5; 0] + randn(3,4); % Four detections in cluster two xFalse = 30*randn(3,2); % Two false alarms x = [x1 x2 xFalse];

Format these detections into a cell array of `objectDetection`

objects.

detections = repmat({objectDetection(0,[0; 0; 0])},10,1); for i = 1:10 detections{i}.Measurement = x(:,i); end

Define the cluster indices according to the previously defined scenario. You can typically obtain the cluster indices by applying a clustering algorithm on the detections.

clusterIndex = [1; 1; 1; 1; 2; 2; 2; 2; 3; 4];

Use the `mergeDetections`

function to merge the detections.

clusteredDetections = mergeDetections(detections,clusterIndex);

Visualize the results in a theater plot.

% Create a theaterPlot object. tp = theaterPlot; % Create two detection plotters, one for unclustered detections and one for % clustered detections. detPlotterUn = detectionPlotter(tp,DisplayName="Unclustered Detections", ... MarkerFaceColor="b",MarkerEdgeColor="b"); detPlotterC = detectionPlotter(tp,DisplayName="Clustered Detections", ... MarkerFaceColor="r",MarkerEdgeColor="r"); % Concatenate measurements and covariances for unclustered detections detArray = [detections{:}]; xUn = horzcat(detArray.Measurement)'; PUn = cat(3,detArray.MeasurementNoise); % Concatenate measurements and covariance for clustered detections clusteredDetArray = [clusteredDetections{:}]; xC = horzcat(clusteredDetArray.Measurement)'; PC = cat(3,clusteredDetArray.MeasurementNoise); % Plot all unclustered and clustered detections plotDetection(detPlotterUn,xUn,PUn); plotDetection(detPlotterC,xC,PC);

## Input Arguments

`detections`

— Object detections

*N*-element array of `objectDetection`

objects | *N*-element cell array of `objectDetection`

objects | *N*-element array of structures

Object detections, specified as an *N*-element array of `objectDetection`

(Sensor Fusion and Tracking Toolbox) objects, *N*-element cell array of
`objectDetection`

objects, or an *N*-element array of
structures whose field names are the same as the property names of the
`objectDetection`

object. *N* is the number of
detections. You can create `detections`

directly, or you can obtain
`detections`

from the outputs of sensor objects such as `fusionRadarSensor`

(Sensor Fusion and Tracking Toolbox), `irSensor`

(Sensor Fusion and Tracking Toolbox), and
`sonarSensor`

(Sensor Fusion and Tracking Toolbox).

`clusterIndex`

— Cluster indices

*N*-element vector of positive integers

Cluster indices, specified as an *N*-element vector of positive
integers, where *N* is the number of detections specified in the
`detections`

input. Each element is the cluster index of the
corresponding detection in the `detections`

input. For example, if
`clusterIndex(i)=k`

, then the `i`

th detection from
the `detections`

input belongs to cluster `k`

.

`mergeFcn`

— Function to merge detections

function handle

Function to merge detections, specified as a function handle. You must use one of these syntaxes to define the function:

Syntax with detection input and output:

detectionOut = mergeFcn(detectionsIn)

where:

`detectionsIn`

is specified as a cell array of`objectDetection`

(Sensor Fusion and Tracking Toolbox) objects (in the same cluster).`detectionOut`

is returned as an`objectDetection`

object.

Syntax with state mean and covariance input and output:

[mergedMean,mergedCovariance] = mergeFcn(means,covariances)

where:

`means`

is specified as an*M*-by-*Q*matrix, representing measurements in the cluster.*M*is the size of each measurement and*Q*is the number of measurements in the cluster.`covariances`

is specified an*M*-by-*M*-by-*Q*matrix, representing the uncertainty covariance matrices corresponding to`means`

.*M*is the size of each measurement and*Q*is the number of measurements in the cluster.`mergedMean`

is returned a*P*-by-1 vector, representing the merged measurement. Note that the size of the merged measurement (*P*) can be different from the size of the input measurement (*M*). This enables you to merge detections into parameterized forms, such as rectangular or cuboid detections.`mergedCovariance`

is returned as a*P*-by-*P*matrix, representing the uncertainty covariance in the merged measurement.*P*is the size of the merged mean.

**Tip**

You can use built-in functions, such as `fusecovint`

(Sensor Fusion and Tracking Toolbox), `fusecovunion`

(Sensor Fusion and Tracking Toolbox), and `fusexcov`

(Sensor Fusion and Tracking Toolbox), as the merging function.

**Example: **`@mergeFcn`

## Output Arguments

`clusteredDetections`

— Clustered detections

*M*-element cell array of `objectDetection`

objects

Clustered detections, returned as an *M*-element cell array of
`objectDetection`

(Sensor Fusion and Tracking Toolbox) objects, where
*M* is the number of unique cluster indices specified in the
`clusterIndex`

input.

## Extended Capabilities

### C/C++ Code Generation

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

The function supports

*non-dynamic memory allocation*code generation. For details, see Generate Code with Strict Single-Precision and Non-Dynamic Memory Allocation (Sensor Fusion and Tracking Toolbox).The function supports

*strict single-precision*code generation. For details, see Generate Code with Strict Single-Precision and Non-Dynamic Memory Allocation (Sensor Fusion and Tracking Toolbox).

## Version History

**Introduced in R2021b**

### R2022b: Specify measurement means and covariances inputs

When you specify the `MergingFcn`

name-value argument, you can now
also specify measurement means and covariances as inputs to the merging function.
Previously, you could use only `objectDetection`

objects or its equivalent structures as
inputs.

## See Also

`clusterDBSCAN`

| `objectDetection`

(Sensor Fusion and Tracking Toolbox)

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