The three thresholds, resolved against a lens.
billboard follows the optics; sphere and surface do not, and that is
not an oversight. They are claims about representation — "a disk with a
terminator on it" and "close enough that the ground is the picture" — and a
player who narrows the lens to a telephoto has not moved closer to the
planet. Only the point-to-billboard step is a statement about pixels.
This is an injectable that earns it: the lens is the one caller with a reason
to construct a set of its own, and every caller without one gets
LOD_THRESHOLDS below. An injectable nobody but the default constructs is a
parameter charged to every signature it threads through, which is what the
shape of selectLod, placeAt and buildScene is guarding against.