The box, in ECEF metres.
[west, south, east, north] in degrees.
Expands all eight corners rather than taking centre-plus-radius. An OBB is oriented: a radius would inflate a long thin tileset — a transport corridor, a coastline, a river survey — into a square many times its true area, and a footprint that says "on screen" when the data is 20 km away defeats the purpose of having one.
No antimeridian handling: a box spanning ±180° comes back as effectively the whole world, which is the safe direction to be wrong in (over-inclusive means "load it", never "skip it"), and the datasets that genuinely straddle it are planet-scale anyway.
The geographic bounds of an ECEF oriented bounding box.