`dunes`¶

Wind-blown dunes added to the terrain: isolated barchans or domes, or fields of transverse, barchanoid or linear crests, with slip faces and optional ripples on them.

Key	Type	Default	Range	Unit	Description
`shape`	one of `barchan`, `dome`, `transverse`, `barchanoid`, `linear`	`"barchan"`			The kind of dune.
`wind_azimuth`	number	`0.0`		rad	Direction the wind blows toward, in radians counter-clockwise from +x (local east of the anchor on a body); slip faces face it.
`azimuth_spread`	number	`0.0`	[0, inf)	rad	Largest difference of each barchan or dome's wind from the azimuth, in radians.
`slip_face_angle`	number	`0.5585053606381855`	(0, 1.5708)	rad	Slope of the lee slip faces, in radians: the sand's angle of repose.
`stoss_slope`	number	`0.17453292519943295`	(0, 1.5708)	rad	Mean slope of the windward faces, in radians; below the slip face angle.
`stoss_exponent`	number	`3.0`	(0, inf)		Exponent alpha of the cos^alpha windward profile of dunes; higher is blunter.
`dome_exponent`	number	`1.8`	(0, inf)		Exponent alpha of the cos^alpha profile of domes.
`spacing`	number	`800.0`	(0, inf)	m	Barchans and domes: side of the lattice cells, each holding at most one dune, in metres.
`density`	number	`0.5`	[0, 1]		Barchans and domes: chance a cell holds a dune, from 0 to 1.
`width`	number	`400.0`	(0, inf)	m	Barchans and domes: mean width, horn to horn, in metres.
`width_spread`	number	`0.3`	[0, 1)		Barchans and domes: each width varies from (1 - spread) to (1 + spread) times the mean, spread in [0, 1).
`min_width`	number	`200.0`	[0, inf)	m	Barchans: width in metres below which a dune is a dome without a slip face, blending into barchans up to 1.5 times it.
`height_ratio`	number	`0.06666666666666667`	(0, inf)		Barchans and domes: height over width.
`horn_length`	number	`9.1`	[0, inf)		Barchans: how far the horns reach downwind of the crest, in dune heights.
`dome_length`	number	`2.0`	(0, inf)		Domes: length along the wind over width.
`wavelength`	number	`550.0`	(0, inf)	m	Transverse, barchanoid and linear dunes: crest-to-crest spacing, in metres.
`height`	number	`20.0`	[0, inf)	m	Transverse, barchanoid and linear dunes: crest height, in metres.
`sinuosity`	number	`0.3`	[0, inf)		Transverse, barchanoid and linear dunes: how far a crest wanders along its length, in wavelengths.
`defects`	number	`0.3`	[0, 1]		Transverse, barchanoid and linear dunes: share of the height that varies along crests, lowering and ending some, from 0 to 1.
`defect_density`	number	`0.0`	[0, inf)	1/m	Transverse, barchanoid and linear dunes: pairs of crest ends per metre of crest, so crests break into segments about 1 / defect_density long; 0 for none. Olympia Undae: 0.0027 (Ewing et al. 2010).
`flank_slope`	number	`0.3490658503988659`	(0, 1.5708)	rad	Linear dunes: mean slope of both flanks, in radians.
`seed`	integer	`1`			Seed of the dunes and ripples; changing it gives a different layout of the same statistics.
`anchor_x`	number	`0.0`			On a body, the longitude in degrees of the point whose tangent frame the dunes are laid out in; they are true to scale near it and absent on the far hemisphere.
`anchor_y`	number	`0.0`			On a body, the latitude in degrees of the anchor.

fade: How dunes too fine for the sample spacing fade out, by samples across their width or wavelength.

Key	Type	Default	Range	Description
`start_samples`	number	`2.0`	[0, inf)	Samples across a feature's diameter up to which it is left out entirely.
`end_samples`	number	`4.0`	(0, inf)	Samples across a feature's diameter from which it is applied in full; it fades in between the two counts.
`shape`	one of `linear`, `smoothstep`, `smootherstep`, `gaussian`	`"smoothstep"`		Curve of the fade between the start and end sample counts.

ripples: Ripples superposed on the dunes.

Key	Type	Default	Range	Unit	Description
`wavelength`	number	`0.0`	[0, inf)	m	Crest-to-crest spacing of the ripples on flat sand, in metres; 0 gives no ripples.
`height`	number	`0.0`	[0, inf)	m	Trough-to-crest height of the ripples on flat sand, in metres.
`lee_fraction`	number	`0.5`	(0, 1)		Share of a ripple wavelength the lee face takes, in (0, 1): 0.5 is symmetric, lower values give a steeper lee face.
`sinuosity`	number	`0.3`	[0, inf)		How far a ripple crest wanders along its length, in wavelengths.
`slope_coupling`	number	`1.0`	[0, inf)		How strongly the dune's slope turns and tightens the ripples: they shorten on steep lee faces and turn on the flanks; 0 keeps them straight across the wind.
`interdune_cover`	number	`0.0`	[0, 1]		Share of the ripple height kept on the ground between dunes, from 0 to 1.
`defect_density`	number	`0.0`	[0, inf)	1/m	Forked crests (Y-junctions): pairs of crest ends per metre of crest, as measured on dune fields (Ewing et al. 2010); 0 for none. Mars large ripples: 0.099.
`flank_straightening`	number	`0.0`	[0, 1]		How far crests straighten off the stoss, from 0 to 1: 1 keeps the sinuosity on flat sand and stoss slopes and takes it away on flanks and lee slopes, as Martian large ripples do.

fade: How ripples too fine for the sample spacing fade out, by samples per wavelength.

Key	Type	Default	Range	Description
`start_samples`	number	`2.0`	[0, inf)	Samples across a feature's diameter up to which it is left out entirely.
`end_samples`	number	`4.0`	(0, inf)	Samples across a feature's diameter from which it is applied in full; it fades in between the two counts.
`shape`	one of `linear`, `smoothstep`, `smootherstep`, `gaussian`	`"smoothstep"`		Curve of the fade between the start and end sample counts.

grainflows: Grainflows on the slip faces: scarps below the brink and lobes below them; off unless cover is set.

Key	Type	Default	Range	Unit	Description
`cover`	number	`0.0`	[0, 1]		Chance, from 0 to 1, that each lattice cell of the slip faces holds a grainflow; 0 for none.
`min_scarp_width`	number	`0.5`	(0, inf)	m	Narrowest scarp, in metres.
`max_scarp_width`	number	`0.5`	(0, inf)	m	Widest scarp, in metres.
`min_scarp_length`	number	`1.0`	(0, inf)	m	Shortest scarp downslope, in metres.
`max_scarp_length`	number	`1.0`	(0, inf)	m	Longest scarp downslope, in metres.
`min_lobe_width`	number	`0.5`	(0, inf)	m	Narrowest lobe, in metres.
`max_lobe_width`	number	`0.5`	(0, inf)	m	Widest lobe, in metres.
`min_lobe_length`	number	`3.0`	(0, inf)	m	Shortest lobe downslope, in metres.
`max_lobe_length`	number	`3.0`	(0, inf)	m	Longest lobe downslope, in metres.
`thickness`	number	`0.015`	[0, inf)	m	Depth of a scarp and height of a lobe, in metres.

fade: How grainflows too narrow for the sample spacing fade out, by samples across a lobe.

Key	Type	Default	Range	Description
`start_samples`	number	`2.0`	[0, inf)	Samples across a feature's diameter up to which it is left out entirely.
`end_samples`	number	`4.0`	(0, inf)	Samples across a feature's diameter from which it is applied in full; it fades in between the two counts.
`shape`	one of `linear`, `smoothstep`, `smootherstep`, `gaussian`	`"smoothstep"`		Curve of the fade between the start and end sample counts.

Every key with its default

{
    "type": "dunes",
    "shape": "barchan",
    "wind_azimuth": 0.0,
    "azimuth_spread": 0.0,
    "slip_face_angle": 0.5585053606381855,
    "stoss_slope": 0.17453292519943295,
    "stoss_exponent": 3.0,
    "dome_exponent": 1.8,
    "spacing": 800.0,
    "density": 0.5,
    "width": 400.0,
    "width_spread": 0.3,
    "min_width": 200.0,
    "height_ratio": 0.06666666666666667,
    "horn_length": 9.1,
    "dome_length": 2.0,
    "wavelength": 550.0,
    "height": 20.0,
    "sinuosity": 0.3,
    "defects": 0.3,
    "defect_density": 0.0,
    "flank_slope": 0.3490658503988659,
    "seed": 1,
    "anchor_x": 0.0,
    "anchor_y": 0.0,
    "fade": {
        "start_samples": 2.0,
        "end_samples": 4.0,
        "shape": "smoothstep"
    },
    "ripples": {
        "wavelength": 0.0,
        "height": 0.0,
        "lee_fraction": 0.5,
        "sinuosity": 0.3,
        "slope_coupling": 1.0,
        "interdune_cover": 0.0,
        "defect_density": 0.0,
        "flank_straightening": 0.0,
        "fade": {
            "start_samples": 2.0,
            "end_samples": 4.0,
            "shape": "smoothstep"
        }
    },
    "grainflows": {
        "cover": 0.0,
        "min_scarp_width": 0.5,
        "max_scarp_width": 0.5,
        "min_scarp_length": 1.0,
        "max_scarp_length": 1.0,
        "min_lobe_width": 0.5,
        "max_lobe_width": 0.5,
        "min_lobe_length": 3.0,
        "max_lobe_length": 3.0,
        "thickness": 0.015,
        "fade": {
            "start_samples": 2.0,
            "end_samples": 4.0,
            "shape": "smoothstep"
        }
    }
}

Used in: example_planets_mars_dunes

dunes¶

`dunes`¶