Describe AOI scene
==================

Once [ArUco markers are placed into a scene](aruco_markers_description.md), areas of interest need to be described into the same 3D referential.

In the example scene, each screen is considered as an area of interest more the blue triangle area inside the top screen.

![AOI description](../../img/aoi_description.png)

All AOIs need to be described from same origin than markers in a [right-handed 3D axis](https://robotacademy.net.au/lesson/right-handed-3d-coordinate-frame/) where:

* +X is pointing to the right,
* +Y is pointing to the top,
* +Z is pointing to the backward.

!!! warning
	All AOIs spatial values must be given in **centimeters**.

### Edit OBJ file description

OBJ file format could be exported from most 3D editors.

``` obj
o YellowSquare
v 6.200003 -7.275252 25.246159
v 31.200003 -7.275252 25.246159
v 6.200003 1.275252 1.753843
v 31.200003 1.275252 1.753843
s off
f 1 2 4 3
o GrayRectangle
v 2.500000 2.500000 -0.500000
v 37.500000 2.500000 -0.500000
v 2.500000 27.500000 -0.500000
v 37.500000 27.500000 -0.500000
s off
f 5 6 8 7
o BlueTriangle
v 12.500002 7.500000 -0.500000
v 27.500002 7.500000 -0.500000
v 20.000002 22.500000 -0.500000
s off
f 9 10 11
```

Here are common OBJ file features needed to describe AOIs:  

* Object lines (starting with *o* key) indicate AOI name.
* Vertice lines (starting with *v* key) indicate AOI vertices.
* Face (starting with *f* key) link vertices together.

### Edit JSON file description

JSON file format allows to describe AOIs vertices.

``` json
{
    "YellowSquare": [[6.2, -7.275252, 25.246159], [31.2, -7.275252, 25.246159], [6.2, 1.275252, 1.753843], [31.2, 1.275252, 1.753843]],
    "GrayRectangle": [[2.5, 2.5, -0.5], [37.5, 2.5, -0.5], [2.5, 27.5, -0.5], [37.5, 27.5, -0.5]],
    "BlueTriangle": [[12.5, 7.5, -0.5], [27.5, 7.5, -0.5], [20, 22.5, -0.5]]
}
```