Provides a two dimensional variant of the three dimensional *AABBTree* object.

Methods of this object are equivalent to those of the *AABBTree* except for obvious changes such as extents being defined with 4 values instead of 6.

This is true also for methods such as *getVisibleNodes* for which the planes are defined
now using 3 values for the normal and distance instead of 4 and
for *getSphereOverlappingNodes* (renamed as getCircleOverlappingNodes
for BoxTree) which takes 2 values to define center of the circle, instead of 3 defining the center of a sphere.

**Required scripts**

The BoxTree object requires:

```
/*{{ javascript("jslib/boxtree.js") }}*/
```