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Enable AOI analysis
===================
The [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) class defines a space where to make matching of gaze movements with AOI and inside which those matchings need to be analyzed.
## Add ArLayer to ArFrame JSON configuration file
An [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) instance can contains multiples [ArLayers](../../argaze.md/#argaze.ArFeatures.ArLayer).
Here is an extract from the JSON [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) configuration file with a sample where one layer is added:
```json
{
"name": "My FullHD screen",
"size": [1920, 1080],
...
"layers": {
"MyLayer": {
"aoi_scene" : {
"upper_left_area": [[0, 0], [960, 0], [960, 540], [0, 540]],
"upper_right_area": [[960, 0], [1920, 0], [1920, 540], [960, 540]],
"lower_left_area": [[0, 540], [960, 540], [960, 1080], [0, 1080]],
"lower_right_area": [[960, 540], [1920, 540], [1920, 1080], [960, 1080]]
},
"aoi_matcher": {
"DeviationCircleCoverage": {
"coverage_threshold": 0.5
}
},
"aoi_scan_path": {
"duration_max": 30000
},
"aoi_scan_path_analyzers": {
"Basic": {},
"TransitionMatrix": {},
"NGram": {
"n_min": 3,
"n_max": 5
}
}
}
}
}
```
!!! note
Timestamped gaze movements identified by parent [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) are passed one by one to each [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer). So, the execution of all [ArLayers](../../argaze.md/#argaze.ArFeatures.ArLayer) is done during parent [ArFrame.look](../../argaze.md/#argaze.ArFeatures.ArFrame.look) method call as explained in [previous chapter](configuration_and_execution.md).
Now, let's understand the meaning of each JSON entry.
### "MyLayer"
The name of the [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer). Basically useful for visualisation purpose.
### AOI Scene
The [AOIScene](../../argaze.md/#argaze.AreaOfInterest.AOIFeatures.AOIScene) defines a set of 2D [AreaOfInterest](../../argaze.md/#argaze.AreaOfInterest.AOIFeatures.AreaOfInterest) registered by name.
### AOI Matcher
The first [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) pipeline step aims to make match identified gaze movement with an AOI of the scene.
The matching algorithm can be selected by instantiating a particular AOIMatcher [from GazeAnalysis submodule](pipeline_modules/aoi_matchers.md) or [from another python package](advanced_topics/module_loading.md).
In the example file, the choosen matching algorithm is the [Deviation Circle Coverage](../../argaze.md/#argaze.GazeAnalysis.DeviationCircleCoverage) which has one specific *coverage_threshold* attribute.
!!! warning "Mandatory"
JSON *aoi_matcher* entry is mandatory. Otherwise, the AOIScanPath and AOIScanPathAnalyzers steps are disabled.
### AOI Scan Path
The second [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) pipeline step aims to build a [AOIScanPath](../../argaze.md/#argaze.GazeFeatures.AOIScanPath) defined as a list of [AOIScanSteps](../../argaze.md/#argaze.GazeFeatures.AOIScanStep) made by a set of successive fixations/saccades onto a same AOI.
Once identified gaze movements are matched to AOI, they are automatically appended to the AOIScanPath if required.
The [AOIScanPath.duration_max](../../argaze.md/#argaze.GazeFeatures.AOIScanPath.duration_max) attribute is the duration from which older AOI scan steps are removed each time new AOI scan steps are added.
!!! note "Optional"
JSON *aoi_scan_path* entry is not mandatory. If aoi_scan_path_analyzers entry is not empty, the AOIScanPath step is automatically enabled.
### AOI Scan Path Analyzers
Finally, the last [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) pipeline step consists in passing the previously built [AOIScanPath](../../argaze.md/#argaze.GazeFeatures.AOIScanPath) to each loaded [AOIScanPathAnalyzer](../../argaze.md/#argaze.GazeFeatures.AOIScanPathAnalyzer).
Each analysis algorithm can be selected by instantiating a particular AOIScanPathAnalyzer [from GazeAnalysis submodule](pipeline_modules/aoi_scan_path_analyzers.md) or [from another python package](advanced_topics/module_loading.md).
In the example file, the choosen analysis algorithms are the [Basic](../../argaze.md/#argaze.GazeAnalysis.Basic) module, the [TransitionMatrix](../../argaze.md/#argaze.GazeAnalysis.TransitionMatrix) module and the [NGram](../../argaze.md/#argaze.GazeAnalysis.NGram) module which has two specific *n_min* and *n_max* attributes.
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