Atmosphere Graph

An Atmosphere Graph describes a planet's whole sky as a node graph: the gas that colours it, the haze and dust in it, the ozone band, low fog, the sun and the cloud layers. You wire nodes together, and a live Sky Preview renders the real atmosphere while you edit. You don't write any code.

One graph drives one atmosphere. Save a graph per planet (AG_Earth, AG_Mars, ...) and swap them to change the look of a world in one step.

Which plugin?

The Atmosphere Graph is part of Metaplanets Creator: Atmosphere (2.1.0 and later). It works on its own, without the terrain plugin, in Unreal Engine 5.6, 5.7 and 5.8. Getting started with the atmosphere actor itself is covered in Adding an Atmosphere.

What you can do with it

• Earth-like skies: blue air, a white horizon, the blue band at twilight, and orange sunsets.
• Other planets: thin, dusty, red-scattering air (Mars); thick nitrogen-methane smog (Titan); hydrogen-helium air; skies tinted by an orange or blue-white star.
• Weather: haze, valley fog with sun shafts, and stacked cloud layers from thin cirrus to cumulonimbus storm decks with rain shafts.
• Alien looks: teal air, violet haze, coloured clouds, a sky that scatters red instead of blue.
• The same sky from the ground to orbit: the preview shows altitudes from 2 m up to 2,000 km, so you can check the limb glow from space and the sky from the surface without leaving the editor.

Create a graph

1. In the Content Browser, right-click and choose Metaplanets → Atmosphere → Atmosphere Graph. Name it with the AG_ prefix, for example AG_MyPlanet.
2. Double-click it. A new graph is not empty: it starts as an Earth starter with Air, Haze, an Absorbing Layer (ozone), a Sun and one Cumulus layer, all wired to the Atmosphere output.
3. Edit nodes and watch the Sky Preview. The graph recompiles automatically 0.2 s after your last change; the Compile button forces it.

The editor

Area	What it does
Graph	The node canvas. Right-click for the node palette (grouped by category). Drag from a pin to list only the nodes that fit it.
Sky Preview	The real atmosphere renderer in a preview world. Pick an altitude (Ground, 3 km, 12 km, 80 km, Orbit) and set Sun elevation, Sun azimuth, View pitch and a fixed Exposure (EV100).
Compiled	Read-only view of the result: planet radius, atmosphere height, ground albedo, every medium, the sun and the cloud layers. Last Compile Message shows an error if the graph didn't compile.
Toolbar	Compile, Copy JSON, Paste JSON.

Pins only connect to pins of the same type (an Air output only goes into an Air input, for example). Float pins have inline number boxes, colour pins have swatches and choice pins have dropdowns. Nodes with many settings hide the advanced ones behind the arrow at the bottom of the node.

The preview has no terrain

The Sky Preview stands on a smooth sphere shaded with the graph's Ground Albedo, looking along the horizon from the pole. It shows exactly how the air, haze and clouds look; place the atmosphere in your level to see it over your planet's terrain.

Use a graph on an atmosphere

Select the Metaplanets Atmosphere Actor, select its AtmosphereComponent, and set Atmosphere Graph (category Atmosphere → Graph) to your asset.

• The graph's air, haze, ozone, fog, sun and planet values replace the component's own settings. They are reapplied every time you edit and recompile the graph, so you can keep the graph editor open next to the level viewport.
• Cloud layers from the graph are created as temporary components (named GraphCloudLayer…). They are rebuilt from the graph when the level loads and are never saved into the level.
• Cloud layers you added by hand stay and render together with the graph's layers. When you switch an existing level over to a graph, untick Enabled on the old hand-placed layers so you don't get both.

With Metaplanets Creator, a sky preset can point at a graph instead. Add this line to the preset's Atmosphere list:

AtmosphereGraph=/Metaplanets/Metaplanets/Sky/AG_Earth.AG_Earth

Node reference

Gases and haze

Air (Rayleigh): the gas itself, scattering short wavelengths more than long ones. This is what makes a clear sky blue and a sunset orange.

Pin	Default	Meaning
Composition	EarthAir	EarthAir, CarbonDioxide, NitrogenMethane or HydrogenHelium. Sets how strongly the gas scatters and its typical scale height (8, 11.1, 40 and 27 km).
Density	1.0	Surface density relative to Earth. Mars is about 0.013, Titan about 4.4, Venus about 65.
ScaleHeight	-1	Height (km) over which the air thins out. -1 uses the composition's typical value.
Tint	white	Per-channel multiplier for stylised skies.

Colored Scattering: an alternative to Air when you want full control of the colour. It plugs into the same Air input.

Pin	Default	Meaning
Strength	13.558	Scattering at 550 nm (green).
WavelengthExponent	4.0	4 = a normal blue sky. 0 = grey, equal at all colours. Negative = red scatters more than blue, so the sky turns warm and the sunset blue (Mars-like).
ScaleHeight	8.0	km.
Tint	white	Per-channel multiplier.

Haze (Mie): aerosols such as dust, smoke and sea salt. Haze whitens the horizon, softens distant terrain and puts a glow around the sun.

Pin	Default	Meaning
Type	EarthAerosol	EarthAerosol, DesertDust, MarsDust, Smoke, VolcanicAsh or Marine. Each type has its own amount, height, glow and colour.
Density	1.0	Multiplier on the type's amount.
HeightScale	1.0	Multiplier on how high the haze reaches.
Absorption	1.0	Multiplier on how much light the particles absorb (darker, browner haze).
Anisotropy	0.0	Added to the type's forward scattering. Higher = a tighter, brighter glow around the sun.
Tint	white	Colour of the scattered light.
AbsorptionTint	white	(advanced) Colour removed by absorption.

Haze type	Character
EarthAerosol	Neutral, low (1.2 km), strong sun glow. The default Earth haze.
DesertDust	Warm beige, reaches 2.5 km, absorbs blue.
MarsDust	Orange-brown, reaches 11 km, strongly absorbs blue.
Smoke	Warm grey-brown, absorbs strongly.
VolcanicAsh	Dense grey, reaches 3 km.
Marine	Bright white sea haze, very low (0.9 km).

Absorbing Layer (Ozone): a band of gas that absorbs light without scattering it. Earth's ozone takes out some red and green, which is why the sky stays deep blue at twilight.

Pin	Default	Meaning
PeakAltitude	25 km	Centre of the band.
Width	15 km	Half-width of the band.
Strength	1.0	0–3.
Tint	white	Per-channel multiplier on the absorbed colours.

Ground Fog: low valley fog and mist, with sun shafts through it.

Pin	Default	Meaning
Density	0.03	Fog at ground level (per km).
ScaleHeight	0.35 km	How quickly it thins with height.
Albedo	(0.75, 0.82, 0.9)	Fog colour.
Anisotropy	0.35	Forward scattering. Higher = stronger sun shafts when looking toward the sun.

Unconnected means off

A medium that isn't wired to the output is switched off: no Air node means no blue sky, no Haze node means a perfectly clear horizon, no Ground Fog node means no fog. Leave a node out on purpose for airless or clear worlds.

Light

Sun: the star's disk and colour.

Pin	Default	Meaning
Illuminance	25	Brightness of the sun used by the Sky Preview and by atmospheres that don't follow a directional light.
AngularRadius	0.268°	Size of the disk. Earth 0.268, Mars 0.18. A close red dwarf might be 1–2.
Color	(1, 0.97, 0.91)	Connect a Star Color node here to set it by temperature.

Star Color (Temperature): a black-body colour from a temperature in Kelvin (1,000–40,000). The Sun is 5,778 K, a red dwarf about 3,000 K and a blue giant about 15,000 K.

In a level, the sky follows your directional light

By default the atmosphere is lit by the level's Directional Light (its intensity and colour), so the sky, clouds and terrain always share one sun. The graph's Sun Illuminance and Color are used in the Sky Preview, and in a level only when Use Sun Light Intensity is turned off on the AtmosphereComponent or there is no directional light. To get a star's colour in a level, set the same colour on the directional light.

Clouds

One node per cloud type, plus Cloud Stack to combine them. Each cloud node outputs one layer; see Clouds: shapes & layers for what every setting does and ready-made recipes.

Node	Default band	Look
Cumulus Clouds	1.5–5 km	Rounded fair-weather clouds.
Stratocumulus Clouds	0.8–2.2 km	Low, flat, lumpy sheets.
Cumulonimbus (Storm) Clouds	1.2–12 km	Towering storm cells with anvils.
Nimbostratus (Rain) Clouds	0.6–4 km	Thick grey rain decks with rain shafts.
Cirrus Clouds	8–11 km	High, thin, wispy ice clouds.
Cloud Stack		Combines any number of layers into one Clouds wire.

A graph can have up to 8 cloud layers.

Values

Node	Use
Float	A number you can wire into several pins.
Color	A colour you can wire into several pins.
Math	Multiply, Add, Subtract, Divide, Min, Max or Power of two numbers.
Color x Float	Scale a colour's brightness.
Color Mix	Blend between two colours (Alpha 0 = A, 1 = B).

Use them to drive several nodes from one control. For example, wire one Color into the Haze Tint and the Ground Fog Albedo so dust and fog always match.

Output

Atmosphere: exactly one per graph.

Pin	Default	Meaning
PlanetRadius	-1	km. -1 keeps the radius set on the actor (recommended when the atmosphere sits on a Metaplanets planet).
AtmosphereHeight	100 km	Top of the atmosphere. Raise it for thick, tall atmospheres (Titan-like: 300–400).
GroundAlbedo	0.4	How much light the ground bounces back into the air. Tint it to match the planet (rusty for Mars).
Air, Haze, Absorber, Fog, Sun, Clouds		Inputs from the nodes above. Clouds takes several wires.

Example skies

These graphs ship as assets in /Metaplanets/Metaplanets/Sky (with Metaplanets Creator) and as JSON in the plugin's Docs/examples/atmosphere folder. Paste the JSON into a new graph with Paste JSON.

Graph	Recipe
AG_Earth	Air, Haze, Ozone, Ground Fog and Sun at their defaults. Cumulus (Coverage 0.38) and Cirrus (0.25) in a Cloud Stack.
AG_Mars	Colored Scattering with Strength 3.2, WavelengthExponent -2.5, ScaleHeight 11.1, so the sky scatters red. Haze MarsDust at Density 0.3. Ground Fog tinted (0.85, 0.6, 0.4). Sun AngularRadius 0.18. No ozone. One thin Cirrus ice layer at 15–24 km, Density 0.008, bluish white. Output: AtmosphereHeight 120, rusty GroundAlbedo (0.45, 0.28, 0.16).
AG_HazyMoon	Titan-like. Air NitrogenMethane, Density 1.2, ScaleHeight 20, amber tint. Haze Smoke with HeightScale 8. Ozone band moved up to 60 km, 40 km wide, tinted to absorb red. Star Color 4,600 K into a large sun (AngularRadius 1.2). A warm Stratocumulus deck lifted to 8–14 km. AtmosphereHeight 400.
AG_Storm	Default Air and Ozone. Haze Density 2.4, HeightScale 1.4, cool tint. Thick Ground Fog (Density 0.09, ScaleHeight 0.5, Anisotropy 0.5). Cumulonimbus (Coverage 0.42) under Stratocumulus (0.55).
AG_Alien	Colored Scattering with WavelengthExponent 1.6 and a teal tint (0.35, 1.0, 0.78). Marine haze tinted violet. Strong ozone band tinted magenta. Star Color 9,500 K (blue-white). Cumulus and Cirrus with coloured MediumAlbedo.
AG_Canopy	A clear forest day: default Air and Ozone, light Haze (Density 0.45), faint low fog (Density 0.008) with strong sun shafts (Anisotropy 0.6), Cumulus 0.3 and Cirrus 0.2.

Haze Density raised to 7: the horizon goes milky and the sun glow spreads. Haze is the quickest way to make a world feel humid, dusty or polluted.

Copy-paste JSON

This is AG_Earth. Copy it, open a new Atmosphere Graph and press Paste JSON:

{
  "format": "MetaplanetsAtmosphereGraph/1",
  "nodes": [
    { "id": "air",   "type": "Air",            "pos": [-460, -320] },
    { "id": "haze",  "type": "Haze",           "pos": [-460, -120] },
    { "id": "ozone", "type": "AbsorbingLayer", "pos": [-460, 90] },
    { "id": "fog",   "type": "GroundFog",      "pos": [-460, 270] },
    { "id": "sun",   "type": "Sun",            "pos": [-460, 460] },
    { "id": "cu",    "type": "CloudCumulus",   "pos": [-900, -340], "values": { "Coverage": 0.38 } },
    { "id": "ci",    "type": "CloudCirrus",    "pos": [-900, 380], "values": { "Coverage": 0.25 } },
    { "id": "stack", "type": "CloudStack",     "pos": [-460, 640] },
    { "id": "out",   "type": "AtmosphereOutput", "pos": [60, 0] }
  ],
  "links": [
    { "from": "air.Air",        "to": "out.Air" },
    { "from": "haze.Haze",      "to": "out.Haze" },
    { "from": "ozone.Absorber", "to": "out.Absorber" },
    { "from": "fog.Fog",        "to": "out.Fog" },
    { "from": "sun.Sun",        "to": "out.Sun" },
    { "from": "cu.Clouds",      "to": "stack.Layers" },
    { "from": "ci.Clouds",      "to": "stack.Layers" },
    { "from": "stack.Clouds",   "to": "out.Clouds" }
  ]
}

And a Mars-like sky with Colored Scattering, dust and one high ice layer wired straight into the output:

{
  "format": "MetaplanetsAtmosphereGraph/1",
  "nodes": [
    { "id": "air",  "type": "ColoredScattering", "values": { "Strength": 3.2, "WavelengthExponent": -2.5, "ScaleHeight": 11.1 } },
    { "id": "haze", "type": "Haze", "values": { "Type": "MarsDust", "Density": 0.3 } },
    { "id": "fog",  "type": "GroundFog", "values": { "Density": 0.02, "ScaleHeight": 0.6, "Albedo": [0.85, 0.6, 0.4], "Anisotropy": 0.4 } },
    { "id": "sun",  "type": "Sun", "values": { "AngularRadius": 0.18 } },
    { "id": "ice",  "type": "CloudCirrus", "values": { "AltitudeInnerKm": 15, "AltitudeOuterKm": 24, "Coverage": 0.2, "Density": 0.008, "MediumAlbedo": [0.85, 0.92, 1.0] } },
    { "id": "out",  "type": "AtmosphereOutput", "values": { "AtmosphereHeight": 120, "GroundAlbedo": [0.45, 0.28, 0.16] } }
  ],
  "links": [
    { "from": "air.Air",    "to": "out.Air" },
    { "from": "haze.Haze",  "to": "out.Haze" },
    { "from": "fog.Fog",    "to": "out.Fog" },
    { "from": "sun.Sun",    "to": "out.Sun" },
    { "from": "ice.Clouds", "to": "out.Clouds" }
  ]
}

JSON format details

• pos is optional. id can be any string; links refer to pins as "<id>.<Pin>".
• Values are numbers, colours as [r, g, b] (or [r, g, b, a]), option names as strings ("MarsDust"), and true / false for on/off pins.
• Missing values use the pin default, out-of-range numbers are clamped, and an unknown option falls back to the first one. An unknown node type fails the paste.
• Copy JSON writes every value as a string and uses generated ids. It looks different from hand-written JSON, but both paste back the same.

Building graphs from the command line

To build many skies from files (for example in a build script), compile JSON into assets headlessly:

UnrealEditor-Cmd MyProject.uproject -run=MetaplanetsAtmosphereGraph -json=C:/Skies/AG_Desert.json -out=/Game/Skies/AG_Desert -dump

-dump prints the compiled result to the log. Exit codes: 1 usage or file error, 2 bad JSON, 3 compile failed, 4 save failed.

Tips for a believable sky

• Air, haze and fog set the planet's character far more than clouds do. Get the clear sky right first, then add clouds.
• Thin air (Density below 0.1) makes a dark sky and a sharp, small sun glow; thick air (above 3) makes a bright, washed-out sky and short views.
• To make a warmer or colder planet, change the star, not just the tints. A Star Color of 4,000–4,600 K warms everything, sky and terrain, consistently.
• Match GroundAlbedo to your terrain's average colour. It changes the colour of the haze near the ground.
• Check every sky at Ground, 12 km and Orbit, and at low sun elevations (0–10°). That is where scattering problems show.

Troubleshooting

Message or symptom	Fix
the graph has no Atmosphere output node	Add the Atmosphere output node.
'Node.Pin' expects A, got B	A wire connects mismatched types. Reconnect it.
the graph has a cycle through 'X'	Remove the loop between value nodes.
The sky has no colour	Nothing is wired into Air.
The sun colour in the level doesn't match the preview	The atmosphere follows the directional light. Set the colour there (see the note under Light).
Clouds sit inside mountains	Cloud altitudes are measured above sea level. Raise the layer's band on mountainous worlds.