secondaries

Secondary craters around the craters of the last crater layer before this one, after Singer et al. (2020).

Key	Type	Default	Range	Unit	Description
seed	integer	0			Seed the secondaries are drawn with; changing it gives a different field of the same statistics.
onset_count	number, optional	null	(0, inf)		Secondaries at least count_fraction primary diameters across, in an area the size of the primary at the onset range. Required: the sources give sizes, not numbers.
count_fraction	number	0.01	(0, inf)		Size, as a fraction of the primary's diameter, from which the onset count counts secondaries.
size_slope	number	4.0	(0, inf)		Cumulative size slope of the secondaries, their number falling as d^-slope; higher values give relatively more small secondaries.
min_diameter	number	1.0	(0, inf)	m	Smallest secondary generated, in metres.
max_diameter	number, optional	null	(0, inf)	m	Largest secondary generated, in metres; unset has no limit beyond Singer et al.'s largest secondary at each range.
outer_range	number, optional	null	(0, inf)		How far secondaries reach, in primary diameters from its centre; unset uses the longest typical ray of Elliott et al. (2018).
min_primary_diameter	number	0.0	[0, inf)	m	Smallest primary crater, in metres, that throws secondaries.
max_primary_diameter	number, optional	null	[0, inf)	m	Largest primary crater, in metres, that throws secondaries; unset has no upper limit.
min_age_gyr	number	0.0	[0, inf)	Gyr	Youngest primary, in Gyr, that throws secondaries.
max_age_gyr	number, optional	null	[0, inf)	Gyr	Oldest primary, in Gyr, that throws secondaries; unset has no upper limit.
manual	boolean	true			Lets manual primary craters throw secondaries too; otherwise only generated ones do.
cell_size_factor	number	16.0	(0, inf)		Side of the polar cells secondaries are drawn in, as a multiple of each size band's largest diameter.
depth_ratio	number	0.11	(0, inf)		Depth over diameter every secondary is given, with no wear by age; lower values give shallower secondaries.
morphometry	one of lunar, mars	"lunar"			Published fits whose fresh crater rim the secondaries are shaped with.

rays: Secondaries gathered into rays and clumped along them; off by default.

Key	Type	Default	Range	Unit	Description
enabled	boolean	false			Gathers secondaries into their primary's rays and clumps them along each ray, as radial chains and clusters; off spreads them evenly.
share	number	0.7	[0, 1]		Share of secondaries in rays, from 0 to 1; the rest stay spread evenly. Illustrative.
min_half_angle_degrees	number	2.0	(0, 90)	deg	Narrowest half width of a ray, in degrees from 0 to 90 excluded, so rays widen with range beyond their width near the primary. Illustrative.
clustering	number	0.8	[0, 1]		How strongly secondaries clump along a ray, from 0 for evenly along it to 1 for only in clumps. Illustrative.
cluster_spacing	number	0.15	(0, inf)		Typical spacing of clumps along a ray, in natural log of range; positive, smaller values give shorter, more frequent clumps. Illustrative.

layout: The rays; give a crater albedo layer's rays the same layout for bright rays over the secondaries.

Key	Type	Default	Range	Unit	Description
seed	integer	0			Seed of the rays' directions; layers with the same layout share the same rays.

count: Number of rays of a crater, drawn per crater and rounded; 0 to 64.

Key	Type	Default	Range	Unit	Description
kind	one of constant, uniform, normal, log_normal	"constant"			Kind of distribution the value is drawn from.
a	number	0.0			The constant value, the uniform's lower bound, the normal's mean or the log-normal's median.
b	number	0.0			The uniform's upper bound, or the standard deviation (of the natural logarithm for a log-normal); unused for a constant.
min	number, optional	null			Lower bound drawn values are clamped to; unset leaves them unbounded below.
max	number, optional	null			Upper bound drawn values are clamped to; unset leaves them unbounded above, which normal and log-normal kinds do not allow.

width_degrees: Angle in degrees a ray spans 2 radii from the centre, drawn per ray, within (0, 180).

Key	Type	Default	Range	Unit	Description
kind	one of constant, uniform, normal, log_normal	"constant"			Kind of distribution the value is drawn from.
a	number	0.0			The constant value, the uniform's lower bound, the normal's mean or the log-normal's median.
b	number	0.0			The uniform's upper bound, or the standard deviation (of the natural logarithm for a log-normal); unused for a constant.
min	number, optional	null			Lower bound drawn values are clamped to; unset leaves them unbounded below.
max	number, optional	null			Upper bound drawn values are clamped to; unset leaves them unbounded above, which normal and log-normal kinds do not allow.

shapes: Secondaries stretched toward their primary; round by default.

Key	Type	Default	Range	Unit	Description
elongated_share	number	0.0	[0, 1]		Share of secondaries, from 0 to 1, stretched along the line back to their primary; 0 keeps them round.

ellipticity: Long over short axis of an elongated secondary near the primary, drawn per secondary; at least 1, falling to 1 at the outer range.

Key	Type	Default	Range	Unit	Description
kind	one of constant, uniform, normal, log_normal	"constant"			Kind of distribution the value is drawn from.
a	number	0.0			The constant value, the uniform's lower bound, the normal's mean or the log-normal's median.
b	number	0.0			The uniform's upper bound, or the standard deviation (of the natural logarithm for a log-normal); unused for a constant.
min	number, optional	null			Lower bound drawn values are clamped to; unset leaves them unbounded below.
max	number, optional	null			Upper bound drawn values are clamped to; unset leaves them unbounded above, which normal and log-normal kinds do not allow.

Every key with its default

{
    "type": "secondaries",
    "seed": 0,
    "onset_count": null,
    "count_fraction": 0.01,
    "size_slope": 4.0,
    "min_diameter": 1.0,
    "max_diameter": null,
    "outer_range": null,
    "min_primary_diameter": 0.0,
    "max_primary_diameter": null,
    "min_age_gyr": 0.0,
    "max_age_gyr": null,
    "manual": true,
    "cell_size_factor": 16.0,
    "rays": {
        "enabled": false,
        "layout": {
            "seed": 0,
            "count": {
                "kind": "normal",
                "a": 10.7,
                "b": 3.1,
                "min": 6.0,
                "max": 20.0
            },
            "width_degrees": {
                "kind": "normal",
                "a": 22.0,
                "b": 8.3,
                "min": 5.4,
                "max": 38.6
            }
        },
        "share": 0.7,
        "min_half_angle_degrees": 2.0,
        "clustering": 0.8,
        "cluster_spacing": 0.15
    },
    "shapes": {
        "elongated_share": 0.0,
        "ellipticity": {
            "kind": "uniform",
            "a": 1.2,
            "b": 1.8,
            "min": null,
            "max": null
        }
    },
    "depth_ratio": 0.11,
    "morphometry": "lunar"
}

Used in: example_craters_secondaries, example_craters_secondary_rays