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Table of Contents

This page discusses the details of the V-Ray Sky map, which is used within the V-Ray Sun and Sky System.


Overview


The VRaySky texture map is typically used as an environment map to help simulate outdoor lighting. The texture can change its appearance based on the position of the VRaySun, which is normally used in conjunction with the V-Ray Sun and Sky System. The first example on the right is a swatch of the sky map with a visible horizon line and ground. The second render on the right is a chrome shader ball rendered with a sky map as an environment along with sun lighting to demonstrate how the sky is reflected in objects.




V-Ray Sky Parameters


The VRaySky texture map is typically used as an environment map, either in the 3ds Max Environment dialogue, or in one of the slots of the V-Ray Environment rollout and behaves very much like an HDRI environment map. The VRaySky changes its appearance based on the position of the VRaySun.

Specify sun node – Specifies how the VRaySky determines its parameters:

Off – The VRaySky automatically takes its parameters from the active VRaySun that was created last. (In other words, if there are multiple suns in the scene, the most recently created VRaySun that is also enabled is used.) In this case, none of the other parameters of VRaySky are accessible.
On
– A different light source can be chosen. It is recommended to use only direct lights, as the vector for the direction is taken into consideration when computing the appearance of the sky. In that case the VRaySun is no longer controlling the VRaySky and the parameters in the texture map rollout determine the final look of the sky.

Sun light – Specifies which light source is chosen if Specify sun node is On.

Turbidity – Refers to VRaySun parameters.

Ozone – Refers to VRaySun parameters.

Intensity multiplier – Refers to VRaySun parameters.

Sky model – Specifies the procedural model used to generate the VRaySky texture.

Preetham et al. – The VRaySky procedural texture is generated based on the Preetham et al. method.
CIE Clear – The VRaySky procedural texture is generated based on the CIE method for clear sky.
CIE Overcast – The VRaySky procedural texture is generated based on the CIE method for a cloudy sky.
Hosek et al.
– The VRaySky procedural texture is generated based on the Hosek et al. method.
PRG Clear Sky (old) – The V-RaySky procedural texture is generated based on the PRG Clear Sky method which has enhanced sunrise and sunset sky.
PRG Clear Sky – The V-RaySky procedural texture is generated using the PRG Clear Sky method. The updated PRG Clear Sky New allows for rendering the sky at various observer altitudes, up to several kilometers. It also supports rendering of nautical twilight effects with sun positions up to 12 degrees below the horizon. Additionally, it features enhanced turbidity control, enabling the rendering of sky conditions with turbidity values ranging from 1.81 to 4.89. See the PRG Clear Sky New examples below.

The PRG Clear Sky model in scenes created with V-Ray 7 cannot be rendered using previous V-Ray versions. 

Indirect horiz. illum. – Specifies the intensity (in lx) of the illumination on horizontal surfaces coming from the sky.

Ground Albedo – Sets the ground color of the V-Ray Sun and Sky system.

Blend angle – Controls the size of the gradient formed by VRaySky between the horizon and the actual sky.

Horizon offset – Offsets the horizon from the default position (the absolute horizon).

Altitude – Controls the observer's altitude in meters. As the altitude increases, sky clarity improves, and the horizon line becomes less defined.


Max2024_VRay7Beta_VRaySky_parameters




Example: Sky Model Types

The images below show the different sky model types. Default values for VRaySky have been used.


Preetham et al.

CIE Clear

CIE Overcast

Hosek et al.

PRG Clear Sky New





Example: PRG Clear Sky New - Turbidity

In this example, you can see how the amount of dust in the air affects the color of the sun and sky.  Smaller values produce a clear image, while higher values dim the sun and sky. 

Example: PRG Clear Sky New - Nautical twilight effect

This example shows how the sun's position affects the sky, creating a twilight effect. Changing the sun's position could require adjusting the Exposure Value as well.



01_PRGNew_Turbidity-2

Turbidity = 2

02_PRGNew_Turbidity-2x6

Turbidity = 2.6

03_PRGNew_Turbidity-3

Turbidity = 3

04_PRGNew_Turbidity-4

Turbidity = 4

05_PRGNew_Turbidity-5

Turbidity = 5

01_PRGNew_EV10_0deg

Exposure Value = 10; Sun below the horizon = 0°

02_PRGNew_EV10_-2deg

Exposure Value = 10; Sun below the horizon = -2°

03_PRGNew_EV10_-4deg

Exposure Value = 10; Sun below the horizon = -4°





Example: PRG Clear Sky New - Altitude

This example shows how the Altitude values affect the visualization of the sky.  Higher Altitude values result in better sky clarity and a less defined horizon line.


01_PRGNew_Altitude-0

Altitude = 0

02_PRGNew_Altitude-1000

Altitude = 1000

03_PRGNew_Altitude-2000

Altitude = 2000

04_PRGNew_Altitude-10000

Altitude = 10000

05_PRGNew_Altitude-15000

Altitude = 15000



Notes


  • Some parameters are hidden from the VRaySky's UI - Sun size multiplier, Sun filter color, and Sun invisible. They are still available in the VRaySun's parameters.
  • V-Ray 7 introduces the PRG Clear Sky New model, which is similar to the old PRG Clear Sky. The old PRG Clear Sky is loaded for scenes containing suns and skies created with previous V-ray versions. The new Sky model is also available in the dropdown menu for old scenes.
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