How much of a pixel a body's diameter covers where it stops being a point.
A third of one, which is deliberately sub-pixel: a star is always smaller than a pixel and must still draw, so the threshold's job is to decide when a point cloud stops being an honest description rather than when something becomes resolvable.
Stated as a fraction of the pixel angle rather than as a constant, because a
constant can only be right at one lens: at the flight lens over the baseline
this is 1.97e-4 of angular radius, at 20° it is 5.44e-5 — a third of it — and
with the zoom channel racked out it is 6.8e-6. The arithmetic is easy to get
wrong by an order of magnitude — a pixel at 60° over 1080 px is atan(1/935),
1.07 mrad, not the 0.2 mrad it is tempting to call one.