A generated body's figure, from the twenty-five that have been measured.
The numbers below are not invented. data/shapes/manifest.json holds
published shape models of everything from a 13 m rock to Vesta, and the
distribution across them is:
min median max
b / a 0.43 0.74 0.99
c / b 0.71 0.87 1.00
rms(r) about the fitted 0.023 0.090 0.61
ellipsoid, over the meanThe third row is the residual after the ellipsoid is taken out, which is
what BodyFigure.irregularity means — the elongation is already carried by
the two rows above it, and measuring the roughness against a sphere would
count it twice.
The one clear trend is the threshold: the two bodies above 200 km — Vesta
and Proteus — have a/c of 1.21 and 1.09, and everything below it is scattered
from 1.05 (Mathilde, a ball) to 2.89 (Eros, a banana) with no strong size
dependence inside the range. So the model is a threshold plus a spread, not
a formula: elongation is switched on below ROUNDING_RADIUS and ramps with
how far below, and within that it is a wide draw, because that is what the
measurements say. A tidy monotonic function of radius would fit the data
worse and look more scientific, which is the wrong trade.
Returns null for a body gravity has rounded — the caller keeps its spheroid, including its rotational flattening, which is a different and real effect.
- rngRng
- Undocumented
- meanRadiusnumber
- Undocumented