uds-fog-and-atmosphere

name	uds-fog-and-atmosphere
description	Configure fog, volumetric fog, dust, and atmospheric coloring in Ultra Dynamic Sky. Covers Fog Density (base + cloud/fog/dust contributions, height falloff, start distance), Fog Color (and the `Support Sky Atmosphere Affecting Height Fog` project setting), Volumetric Fog with light scattering, the Global Volumetric Material (3D noise, ground fog, water-level fog), Dust, the Sky Atmosphere settings (Rayleigh scattering, absorption, overcast luminance), and Simplified Color mode for cheaper sky shading. Use whenever the user mentions UDS fog, height fog, volumetric fog, atmospheric scattering, sky color tinting, dust/sand haze, ground fog, fog below water, or sees a "hard line where fog suddenly starts" issue.
metadata	{"asset":"Ultra Dynamic Sky (marketplace)","category":"atmosphere","source-docs":"https://www.ultradynamicsky.com/Documentation/V9/9-5"}

UDS fog and atmosphere

UDS owns three air-shading systems — height fog, volumetric fog, and the global volumetric material — plus a sky-coloring layer with two backends. This skill covers each and the interactions between them.

System	Category	What it does	Cost
Height fog (density)	Fog Density	Distance-based opacity, height falloff, start distance	Cheap
Height fog (color)	Fog Color	Tint of the height fog (overridden by Sky Atmosphere by default)	Cheap
Volumetric Fog	Volumetric Fog	3D fog receiving local light, scatters	Expensive
Global Volumetric Material	Volumetric Fog	3D noise extinction, ground fog, underwater extinction	Adds cost on top of Volumetric Fog
Dust	Dust	Imitates dust/smoke/particulates in the air (affects fog density + color)	Cheap
Sky Atmosphere	Sky Atmosphere	Realistic atmospheric scattering (default Color Mode)	Costlier than Simplified
Simplified Color	Simplified Color	LUT-based sky coloring with adjustable color values	Cheap

When to use this skill

• Tuning how thick fog gets with cloud coverage / weather / dust.
• Making fog look different per weather (cloudy, foggy, dusty).
• Enabling volumetric fog and dealing with its cost.
• Adding ground fog or 3D noise variation to the fog.
• Setting up underwater fog tinting/extinction.
• Picking between Sky Atmosphere and Simplified Color for sky shading.
• Tuning sunset/twilight color, Rayleigh scattering, or overcast luminance.
• Diagnosing a hard fog line, sky flickering black, or pixelated volumetric fog.

Fog Density

Category: Fog Density. Derives the height fog component's density, falloff, and start distance from inputs like Cloud Coverage, Fog, and Dust Amount.

Output	How it's derived
Density	Base value + contributions added for Cloud Coverage, Fog, Dust Amount
Height Falloff	Base value + separate falloffs for cloudy / foggy / dusty (used directly, not summed)
Start Distance	Derived from current density. A start distance at low density + a density value at which start distance reduces to 0 (fog right up to the camera)

Increasing Cloud Coverage / Fog / Dust automatically thickens distance fog. For different moods per weather, tune the per-state contributions in this category.

Fog Color

Category: Fog Color. The project setting Support Sky Atmosphere Affecting Height Fog is what determines whether these settings are actually used.

Project setting state	Result
Enabled (typical default, recommended)	Height fog colors come directly from the sky atmosphere. Most Fog Color settings on UDS are ignored.
Disabled	Fog uses Fog Color settings only. Use for full direct control.

This dependency disappears entirely if Color Mode = Simplified Color — Simplified Color doesn't enable the sky atmosphere, so all Fog Color settings are live.

Path Tracer distance fog

Render Height Fog In Path Tracer Using Post Process (in Fog Color category, on by default). Lets the path tracer approximate distant height fog via post process — the path tracer otherwise lacks native height fog support. See uds-cinematics-rendering.

Volumetric Fog

Unreal's volumetric fog renders advanced fog nearby the camera that receives/scatters light from local sources and supports variable color/extinction via volumetric materials. Enable from the Volumetric Fog category.

Setting	Effect
Enable	Master toggle
Overall extinction	How dense the volumetric fog is
Distance from camera	How far volumetric fog renders
Volumetric Scattering Intensity (sun + moon)	How brightly each light source lights the volumetric fog

Performance and scalability

Volumetric Fog is expensive. Notes:

Fact	Consequence
Volumetric Fog is a renderer feature	Scalability comes from the Shadow Quality group
Default scalability for Low and Medium disables volumetric fog	Many users won't see it on their hardware unless quality is High+
UDS's Global Volumetric Material adds cost on top	Cost increases noticeably with global material on

Global Volumetric Material

Also in Volumetric Fog category. Adds global controls of extinction and color.

Feature	What it adds
Texture-based 3D noise	Variation to the fog extinction
Weather Mask brush masking	Mask volumetric fog where Weather Mask Brush / Projection Box actors are placed. See udw-material-and-screen-effects.
Ground fog	Additional extinction directly above distance fields. Requires project setting that generates mesh distance fields.
Underwater extinction + albedo	Applied below the water level set in Water Level category. See uds-modifiers-configs-state.

Dust

Category: Dust. Imitates dust/smoke/particulates in the air.

Variable	Effect
Dust Amount	Affects fog density, height falloff, fog color
Dust Color	Color used for fog when Dust Amount = 1
Density-specific settings	In the Fog Density category

If UDW is in the scene, UDW takes control of Dust Amount as part of weather state.

Sky Atmosphere

When Color Mode = Sky Atmosphere (default), main sky color comes from the Sky Atmosphere category.

Setting	Drives
Rayleigh Scattering (day / night / dawn-dusk)	Main sky color. Adjustable per time band.
Sunset/Sunrise, Twilight	The sky atmosphere component's Absorption setting. Use for stronger colored sunsets, altered twilight tone.
Sky Atmosphere Overcast Luminance	Scales intensity of all sky colors when Cloud Coverage is high

Simplified Color

When Color Mode = Simplified Color, main sky color comes from the Simplified Color category. Cheaper at the material level than Sky Atmosphere, more directly tweakable.

Setting	Drives
Color variables (base sky, light/dark cloud)	2D Dynamic Clouds and Static Clouds cloud colors. (Volumetric cloud color is in the Volumetric Clouds category.)
Directional Intensity (float curve)	How directional light intensity dims as it nears the horizon
Directional Light Scattering (color curve)	How directional light color is filtered as it nears the horizon
Sun / Moon atmosphere LUT textures	Volume textures sampled by the sky material to derive atmospheric colors from camera vector and sun/moon orientation

The LUT textures are involved to author from scratch. For tweaks, prefer doing color transforms on the included textures.

Runtime / Blueprint control

// Active properties — set directly, cache picks up:
UDS.Fog          = 0.4    // (use UDW instead if present)
UDS.CloudCoverage = 0.7
UDS.DustAmount   = 0.2

// Volumetric fog enable / extinction / distance — many are static:
UDS.bEnableVolumetricFog = true
UDS.CallStaticPropertiesVolumetricFog()   // apply

If a runtime change has no effect, look for the matching Static Properties - <Category> function and call it. Last-resort full refresh: Hard Reset Cache. See uds-performance-mobile-troubleshooting.

Performance

Lever	Effect
Use Color Mode = Simplified Color	Skips Sky Atmosphere; cheaper sky material
Disable Volumetric Fog	Big win — Volumetric Fog is expensive
Disable Global Volumetric Material	Saves the cost added on top of Volumetric Fog
Disable Ground Fog feature	Avoid the distance-field tracing cost

Gotchas

• Hard line where fog/atmosphere suddenly starts — sky atmosphere position is wrong relative to the scene. Place UDS at ground level so the camera is never significantly below the UDS actor.
• Sky color flickers black when moving the camera — engine bug; camera dipped below the sky atmosphere "ground". Select the Sky Atmosphere component on UDS (in the top components list) and move it down below the lowest point the camera can reach.
• Volumetric fog pixelated / low quality — that's project scalability. Volumetric fog's scalability cvars are in the Shadow Quality group. UDS doesn't override them.
• Volumetric fog completely invisible — default Low/Medium engine scalability disables volumetric fog entirely. Check scalability settings.
• Fog Color changes have no effect — Support Sky Atmosphere Affecting Height Fog project setting is on, so fog colors come from the sky atmosphere. Either disable the project setting or switch Color Mode to Simplified Color.
• Dust Amount ignored on UDS — UDW is in the scene; UDW's weather state owns it.
• Ground Fog feature has no effect — project setting to generate mesh distance fields is off. Enable it.

References & source material

Docs (Ultra Dynamic Sky 9.5):

• Fog Density
• Fog Color
• Volumetric Fog (incl. Global Volumetric Material)
• Dust
• Sky Atmosphere
• Simplified Color
• Common Issues — General Rendering

Related skills: uds-setup-and-modes, uds-clouds, uds-modifiers-configs-state (water level), uds-cinematics-rendering, udw-particles-lightning-wind-sounds (UDW Dust flows into UDS Dust Amount), udw-material-and-screen-effects (Weather Mask masking applies to Global Volumetric Material).