How many pixels one grid cell of a patch may cover before it is refined.
Less of a dial than it looks, once the tree is restricted. A balanced quadtree grading from the level underfoot out to the level at the horizon has a floor of its own — standing on Miranda at the flight lens, 408 patches at 32 px and 414 at 24 — and below about sixteen pixels the error predicate starts adding on top of it: 438 at 16, 597 at 8, 720 at 6. So this sits where the two curves meet.
Measured at 16 px, at the flight lens over 1080 display pixels, standing at two meters: 294 patches on Earth, 330 to 438 across the zoo — 1.24 to 1.85 M vertices, which at four vec3 attributes is 60 to 89 MB of vertex buffers, and 2.4 to 3.6 M triangles selected, of which the renderer's own frustum culling draws roughly a third. Packing the four vertex attributes below float32 is worth about half the memory and frustum-culling the selection about half again; both are measured-before-optimized rather than done here.
The near field does not depend on this at all: the patch underfoot is at
maxLevel, where the predicate is switched off, so what this decides is how
fast detail falls away with distance.