corners

Where the overlay's image corners land, with the box's <rotation> applied.

KML's rotation is degrees counter-clockwise about the box centre. The rotation happens in a locally-scaled frame — longitude offsets shrunk by cos(latitude) — so a rotated box keeps its shape on the ground instead of shearing with latitude. Exact enough for the tile-sized overlays this feature exists for; a continent-sized rotated overlay would drift, and nothing exports one.