r-tree how to calculate minimum bounding rectangles of non leaf nodes

Question

I have many building footprints and want to store them in a r-tree structure.I want to understand that in a r-tree structure leaf nodes are minimum bounding rectangles (MBR) of real objects, in my case building footprints. But I could not understand how MBRs of non leaf nodes can be calculated and I want to know how can it be done (In the picture Green boxes). I suppose there are many possible solution but I just want to know only one of them.

Answer 1

The bounding boxes of inner nodes are computed exactly the same way as for leaf nodes.

You need the minimum and maximum in each axis.