Enumerations

The named values fields choose between.

aging

Value	Meaning
freshness	Blocks wear away with the crater's freshness (current over fresh depth): all when fresh, none at or below the minimum freshness.
age	Blocks wear away with the crater's age as (1 - age / lifetime)^exponent, synthterrain's form.

basis

Value	Meaning
perlin	Improved Perlin gradient noise: smooth, general-purpose relief.
simplex	Simplex gradient noise: smooth relief, an alternative to Perlin.
value	Value noise: random values interpolated over a lattice; blockier than gradient noise.
worley_f1	Cellular noise from the distance to the nearest feature point: cones and basins.
worley_f2	Cellular noise from the distance to the second-nearest feature point.
worley_f2_minus_f1	Cellular noise F2 - F1: ridges along cell borders, like cracked ground.
voronoi	Voronoi cells, each at one random height: flat polygonal plateaus and terraces.

blend

Value	Meaning
add	Adds the layer to the height so far.
max	Keeps the higher of the height so far and the layer.
min	Keeps the lower of the height so far and the layer.
mask	Multiplies the height so far by (layer / amplitude + 1) / 2, so the layer modulates roughness by region.

chronology

Value	Meaning
neukum	Neukum et al. (2001) lunar chronology, for surfaces 0 to 4.6 Gyr old.
ivanov	Ivanov (2001) Martian chronology, for surfaces 0 to 4.6 Gyr old.

compression

Value	Meaning
none	Uncompressed: the largest files.
lzw	Lossless LZW compression, widely supported.
deflate	Lossless Deflate (zlib) compression.
packbits	PackBits run-length compression; read only, so outputs cannot use it.

curve

Value	Meaning
minimum	The model's minimum curve: the fewest boulders.
nominal	The model's nominal curve.
maximum	The model's maximum curve: the most boulders.

datum

Value	Meaning
none	No datum: the crater profile is added onto the terrain everywhere.
plane	Interior cut relative to a least-squares plane over the fit footprint, keeping regional slopes.
mean_height	Interior cut relative to a flat datum at the mean height over the fit footprint.
centre_height	Interior cut relative to a flat datum at the terrain height under the crater centre.

diffusivity

Value	Meaning
matched	The Fassett et al. (2022) diffusivity fitted to the steady-state ages' equilibrium (Trask or Hartmann), so craters wear as that equilibrium expects; Hartmann's for other ages.
fassett_2022_hartmann	Lunar size-dependent diffusivity of Fassett et al. (2022) for the Hartmann equilibrium, 3.6 D^0.87 m^2/Myr with D in km.
fassett_2022_trask	Lunar size-dependent diffusivity of Fassett et al. (2022) for the Trask equilibrium, 3.1 D^1.05 m^2/Myr with D in km.
fassett_thomson_2014	Lunar diffusivity of Fassett and Thomson (2014), 5.5 m^2/Myr for every crater size; it erases craters below a few hundred metres within a small share of their lifetimes.
fassett_thomson_2014_calibration	Fassett and Thomson's (2014) lunar diffusion age against crater age, independent of size; suits kilometre-scale craters.
power_law	A diffusivity of your own, coefficient (D / 1 km)^exponent m^2/Myr, from the power_law settings.

equilibrium

Value	Meaning
trask	Trask (1966) lunar equilibrium, N(>=D) = 10^-1.1 D^-2, as the DSNE uses.
hartmann	Hartmann (1984) lunar equilibrium, N(>=D) = 10^-1.14 D^-1.83 per km^2 with D in km.

format

Value	Meaning
csv	Comma-separated values, one row per item.
json	A JSON document.

fractal

Value	Meaning
fbm	Fractional Brownian motion: a weighted sum of octaves, the general-purpose choice.
ridged	Ridged multifractal: sharp crests from inverted absolute noise, like eroded ridges.
billow	Sum of absolute-value octaves: rounded, puffy forms.
hybrid_multifractal	Hybrid multifractal: smooth lowlands and rough highlands.

kind

Value	Meaning
constant	Always a.
uniform	Uniform between a and b.
normal	Normal with mean a and standard deviation b.
log_normal	Log-normal with median a and standard deviation b of the natural logarithm.

measure

Value	Meaning
scale	The local density over the layer's own; 1 keeps it as the size distribution gives it.
count	Features with diameters in the map's range per area unit, such as boulders per km^2.
areal_fraction	Share of the ground covered by features in the map's range, such as rock abundance.

measure

Value	Meaning
exponent	The cumulative exponent alpha, counts falling as D^-alpha.
mean_diameter	The mean diameter in metres of the features from the reference diameter up, from which alpha = mean / (mean - D0).

model

Value	Meaning
power_law	Rim harmonics with amplitudes falling as a power of the harmonic number, of a given RMS: a simple, configurable spectrum.
du_2024	The fitted rim-crest spectra of fresh lunar craters of Du et al. (2024), from each crater's diameter.

model

Value	Meaning
intercrater	0.0001 D^-1.75457 per m^2 with D in metres: synthetic_moon's "low blockiness".
haworth	0.002 D^-2.6607 per m^2 with D in metres: synthetic_moon's "high blockiness".
viper_specification	0.0003 D^-2.482 per m^2 with D in metres: the VIPER Environmental Specification.

model

Value	Meaning
nearest	One centre per cell of a jittered lattice, each point weighted by its nearest centre only.
thomas	A Thomas cluster process: Poisson-scattered centres whose Gaussian clusters add where they overlap.

morphometry

Value	Meaning
lunar	Fresh lunar craters: Fassett et al. (2022) depth and rim height below 15 km, Pike's (1977) complex crater fits above.
mars	Fresh Martian craters: depth and rim height capped for small craters, Garvin et al.'s (2003) fits for large and complex craters from 7 km.

order

Value	Meaning
oldest_first	Oldest craters first, then larger first: the physical order, so younger craters overprint older ones.
largest_first	Largest craters first, then older first, so smaller craters overprint larger ones.

production

Value	Meaning
neukum	Neukum et al. (2001) lunar production function, valid from 10 m to 300 km.
extended_neukum	The Neukum production function continued below 10 m as a power law of slope -2.85, valid from 2.5 m to 300 km.
ivanov	Ivanov (2001) Martian production function, valid from 15 m to 362 km.

profile

Value	Meaning
smoothstep	Every block inside the rim, falling along a smoothstep to none at the reach.
exponential	Exponential decay outside the rim, a fixed share on the floor and none beyond the reach: synthterrain's crater probability map.

reference

Value	Meaning
none	No parameters: each class present must be given.
mars_pancam	Pancam fits at 753 nm (Johnson et al. 2006a, b, tabulated by Fernando et al. 2013): soil, sand, dust, bedrock (Eagle crater outcrop, Johnson et al. 2006b) and rock.

relief

Value	Meaning
dome	Each boulder's exposed part drawn as a dome: cheap, and enough for small boulders.
shape	The top surface of each boulder's 3D boulder shape drawn into the heights.
none	No rock relief in the heights, only fillets when set, for programs that place every boulder as a model of its own.

resampling

Value	Meaning
nearest	The value of the nearest cell centre: blocky, but never mixes values.
bilinear	Linear in each axis over the four surrounding cells.
cubic	Keys cubic convolution over the sixteen surrounding cells: the smoothest, for upscaling DEMs.

rim

Value	Meaning
original	The published fits, whose interior and exterior meet at 0.98 radii.
at_one_radius	Interior fit extended to 1.0 radii so the rim lies at the stated diameter, as synthterrain's FT_Crater; leaves a small step at the rim.
plateau	A flat rim at the fresh rim height from 0.98 to 1.02 radii, after Fassett et al. (2022), as synthterrain's FTmod_Crater.

shape

Value	Meaning
linear	Straight ramp: continuous, with kinks at both ends.
smoothstep	Cubic 3t^2 - 2t^3: continuous slope across the transition.
smootherstep	Quintic 6t^5 - 15t^4 + 10t^3: continuous slope and curvature, the smoothest join.
gaussian	Gaussian falloff with sigma a third of the band, rescaled to end at zero.

shape

Value	Meaning
barchan	Isolated crescents with a slip face and horns downwind; domes below min_width.
dome	Isolated rounded heaps without a slip face.
transverse	Continuous crests across the wind, each with a slip face.
barchanoid	Transverse crests bent into linked crescents, as where sand supply rises.
linear	Symmetric crests along the wind, as under two winds on scarce sand.

solid

Value	Meaning
icosahedron	Boulders start from an icosahedron, twenty triangles on the unit sphere: rounder shapes.
cube	Boulders start from a cube: blocky shapes.
pyramid	Boulders start from a square-based pyramid.
prism	Boulders start from a triangular prism, a wedge.
tetrahedron	Boulders start from a regular tetrahedron: angular shapes.

terrain

Value	Meaning
rough_mare	Moore's rough mare crater distribution: 10^-1 D^-2 per m^2 below 100 m, 10 D^-3 above.
smooth_mare	Moore's smooth mare crater distribution: 10^-1 D^-2 per m^2 below 40 m, then D^-3, D^-1.68 from 100 m and D^-3 from 200 m.
uplands	Moore's uplands crater distribution: 10^-1 D^-2 per m^2 below 1 km, 10^2 D^-3 above.
heavily_cratered	Moore's heavily cratered distribution: 10^-1 D^-2 per m^2 up to 10 km.