A level-of-detail ring selected by cell centre must overlap its neighbour by more than one cell

Fact

Concentric level-of-detail rings are usually built by generating each level's grid and keeping the cells whose centre falls between an inner and an outer radius. A centre inside the boundary keeps a cell whose far half sticks out past it, and a centre outside drops a cell whose near half should have been drawn. The uncovered band is therefore up to half a cell wide on each side — and the coarse level's cell is the large one.

So the overlap between two rings has to be measured in the coarser level's cells, not as a percentage of the radius. A 6% overlap at a 3600 m boundary is 216 m, while the ring outside it has 1100 m cells: guaranteed gaps. Start each ring at previousRadius - cell * 1.2 and the wedges close.

Why it matters

What shows through the gap is the background, and a sky or haze colour drawn in a thin sliver below the horizon does not read as a hole. It reads as water, as a cloud shadow, or as a lit field, so the bug is investigated as a colour or sorting problem in the terrain rather than as missing geometry.

The gaps also move with the camera, because each level snaps its grid to a different multiple, which makes them look like flicker rather than absence.

How to apply

• Derive the inner radius from the cell size: inner = prevRadius - cell * 1.2.
• Let the rings overlap and settle the tie deliberately — push the coarse ring back in the depth sort so the finer quads always paint last.
• Test it without rendering: sweep the radius and assert that some level's [inner, outer] band, widened by its own cell size, contains every value.