Enable AOI analysis
===================

Once [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) is [configured](configuration_and_execution.md) and [2D AOI are described](aoi_2d_description.md), fixation can be matched with AOI to build an AOI scan path before analyzing it. 

![Layer](../../img/ar_layer.png)

## Add ArLayer to ArFrame JSON configuration file

The [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) class defines a space where to make matching of fixations with AOI and inside which those matchings need to be analyzed.

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" : {
			    "GeoSector": [[860, 160], [1380, 100], [1660, 400], [1380, 740], [1440, 960], [920, 920], [680, 800], [640, 560]],
			    "LeftPanel": {
			        "Rectangle": {
			            "x": 0,
			            "y": 0,
			            "width": 350,
			            "height": 1080
			        }
			    },
			    "CircularWidget": {
			        "Circle": {
			            "cx": 1800,
			            "cy": 120,
			            "radius": 80
			        }
			    }
        	},
        	"aoi_matcher": {
                "argaze.GazeAnalysis.DeviationCircleCoverage.AOIMatcher": {
                    "coverage_threshold": 0.5
                }
            },
        	"aoi_scan_path": {
        		"duration_max": 30000
        	},
			"aoi_scan_path_analyzers": {
				"argaze.GazeAnalysis.Basic.AOIScanPathAnalyzer": {},
				"argaze.GazeAnalysis.TransitionMatrix.AOIScanPathAnalyzer": {},
				"argaze.GazeAnalysis.NGram.AOIScanPathAnalyzer": {
					"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.

### *layers*

An [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) instance can contains multiples [ArLayers](../../argaze.md/#argaze.ArFeatures.ArLayer) stored by name.

### MyLayer

The name of an [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer). Basically useful for visualisation purpose.

### *aoi_scene*

The set of 2D AOI into the layer as defined at [2D AOI description chapter](aoi_2d_description.md).

![AOI scene](../../img/aoi_2d_description.png)

### *aoi_matcher*

The first [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) pipeline step aims to make match identified gaze movement with a layer's AOI.

![AOI matcher](../../img/aoi_matcher.png)

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](../../argaze.md/#argaze.GazeFeatures.AOIScanPath) and [AOIScanPathAnalyzers](../../argaze.md/#argaze.GazeFeatures.AOIScanPathAnalyzer) 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.

![AOI scan path](../../img/aoi_scan_path.png)

Once 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](../../argaze.md/#argaze.GazeFeatures.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.