Add a heatmap
=============

Heatmap is an optional [ArFrame](../../argaze.md/#argaze.ArFeatures.ArFrame) pipeline step. It is executed at each new gaze position to update heatmap image.

![Heatmap](../../img/heatmap.png)

## Enable and display ArFrame heatmap

[ArFrame.heatmap](../../argaze.md/#argaze.ArFeatures.ArFrame.heatmap) can be enabled thanks to a dedicated JSON entry.

Here is an extract from the JSON ArFrame configuration file where heatmap is enabled and displayed:

```json
{
    "argaze.ArFeatures.ArFrame": {
        "name": "My FullHD screen",
        "size": [1920, 1080],
        ...
        "heatmap": {
            "size": [320, 180],
            "sigma": 0.025,
            "buffer": 0
        },
        ...
        "image_parameters": {
            ...
            "heatmap_weight": 1
        }
    }
}
```
!!! note
    [ArFrame.heatmap](../../argaze.md/#argaze.ArFeatures.ArFrame.heatmap) is automatically updated each time the [ArFrame.look](../../argaze.md/#argaze.ArFeatures.ArFrame.look) method is called. As explained in [visualization chapter](visualization.md), the resulting image is accessible thanks to [ArFrame.image](../../argaze.md/#argaze.ArFeatures.ArFrame.image) method.

Now, let's understand the meaning of each JSON entry.

### *size*

The heatmap image size in pixel. Higher size implies higher CPU load.

### *sigma*

The gaussian point spreading to draw at each gaze position.

![Point spread](../../img/point_spread.png)

### *buffer* 

The size of point spread images buffer (0 means no buffering) to visualize only last N gaze positions.

### *heatmap_weight*

The weight of heatmap overlay in [ArFrame.image](../../argaze.md/#argaze.ArFeatures.ArFrame.image) between 0 and 1.