Project AOI into camera frame
=============================

Once [ArUcoScene pose is estimated](pose_estimation.md) and [AOI are described](aoi_description.md), AOI can be projected into [ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) frame.

![AOI projection](../../img/aruco_camera_aoi_projection.png)

## Add ArLayer to ArUcoScene to load AOI

The [ArLayer](../../argaze.md/#argaze.ArFeatures.ArLayer) class allows to load areas of interest description. An [ArUcoScene](../../argaze.md/#argaze.ArUcoMarkers.ArUcoScene) instance can contains multiples [ArLayers](../../argaze.md/#argaze.ArFeatures.ArLayer).

Here is the previous extract where one layer is added to the [ArUcoScene](../../argaze.md/#argaze.ArUcoMarkers.ArUcoScene) configuration:

```json
{
    "name": "My FullHD camera",
    "size": [1920, 1080],
    ...
    "scenes": {
        "MyScene" : {
            "aruco_markers_group": {
                ...
            },
            "layers": {
                "MyLayer": {
                    "aoi_scene": {
                        "YellowSquare": [[6.2, -7.275252, 25.246159], [31.2, -7.275252, 25.246159], [31.2, 1.275252, 1.753843], [6.2, 1.275252, 1.753843]],
                        "GrayRectangle": [[2.5, 2.5, -0.5], [37.5, 2.5, -0.5], [37.5, 27.5, -0.5], [2.5, 27.5, -0.5]],
                        "BlueTriangle": [[12.5, 7.5, -0.5], [27.5, 7.5, -0.5], [20, 22.5, -0.5]]
                    }
                }
            } 
        }
    }
    ...
}
```

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 3D [AreaOfInterest](../../argaze.md/#argaze.AreaOfInterest.AOIFeatures.AreaOfInterest) registered by name.

## Add ArLayer to ArUcoCamera to project AOI

Here is the previous extract where one layer is added to the [ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) and displayed:

```json
{
    "name": "My FullHD camera",
    "size": [1920, 1080],
    ...
    "scenes": {
        "MyScene" : {
            "aruco_markers_group": {
                ...
            },
            "layers": {
                 "MyLayer": {
                    "aoi_scene": {
                        ...
                    }
                } 
            } 
        }
    },
    "layers": {
        "MyLayer": {}
    }
    ...
    "image_parameters": {
        ...
        "draw_layers": {
            "MyLayer": {
                "draw_aoi_scene": {
                    "draw_aoi": {
                        "color": [255, 255, 255],
                        "border_size": 1
                    }
                }
            }
        }
    }
}
```

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.

!!! warning "Layer name policy"

    An [ArUcoScene](../../argaze.md/#argaze.ArUcoMarkers.ArUcoScene) layer is projected into [an ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) layer, **provided they have the same name**.

!!! note

    [ArUcoScene](../../argaze.md/#argaze.ArUcoMarkers.ArUcoScene) layers are projected into their dedicated [ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) layers when calling the [ArUcoCamera.watch](../../argaze.md/#argaze.ArFeatures.ArCamera.watch) method.

## Add AOI analysis

When a scene layer is projected into a camera layer, it means that the 3D [ArLayer.aoi_scene](../../argaze.md/#argaze.ArFeatures.ArLayer.aoi_scene) description of the scene becomes the 2D camera's [ArLayer.aoi_scene](../../argaze.md/#argaze.ArFeatures.ArLayer.aoi_scene) description of the camera.

Therefore, it means that [ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) benefits from all the services described in [AOI analysis pipeline section](../gaze_analysis_pipeline/aoi_analysis.md).

Here is the previous extract where AOI matcher, AOI scan path and AOI scan path analyzers are added to the [ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) layer:

```json
{
    "name": "My FullHD camera",
    "size": [1920, 1080],
    ...
    "scenes": {
        "MyScene" : {
            "aruco_markers_group": {
                ...
            },
            "layers": {
                 "MyLayer": {
                    "aoi_scene": {
                        ...
                    }
                } 
            } 
        }
    },
    "layers": {
        "MyLayer": {
            "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
                }
            }
        }
    }
    ...
}
```

!!! warning

    Adding scan path and scan path analyzers to an [ArUcoCamera](../../argaze.md/#argaze.ArUcoMarkers.ArUcoCamera) layer doesn't make sense if the camera is moving.