©BBB3viz

This page describes the use of V-Ray's physically accurate sun and sky system.

 

Overview


The VRaySun and VRaySky are special features which are provided by the V-Ray renderer. Developed to work together, the VRaySun and VRaySky reproduce the real-life Sun and Sky environment of the Earth. Both are coded so that they change their appearance depending on the direction of the VRaySun. Refer to the VRaySky page for more details about the texture.

The V-Ray Sun and Sky are based largely on the model presented in [ 1 ]. For a more complete list of references, please see the References and links section.

 

UI Path: ||Create menu|| > Lights > V-Ray...

 

||V-Ray Toolbar|| > V-Ray Sun button > Click and drag in a viewport

 

||V-Ray menu|| > Create > Lights > V-Ray Sun


||Create menu|| > Lights > V-Ray > V-Ray Sun > Click and drag in a viewport


||Command panel|| > Create tab > Lights > Choose V-Ray from dropdown > VRaySun > click and drag in a viewport

 


Image courtesy of Tamas Medve

 

 


 

Example: Direction of the VRaySun Light


This example demonstrates the effect of the sun direction. The Sun is positioned such as its rays hit the ground at certain degrees. Note how in addition to the scene brightness, the sun position also changes the appearance of the sky and the sun light color. 

 

5 degrees

25 degrees

45 degrees

90 degrees

5
90

 


Sun Parameters


You can also specify the VRaySun as the sun type inside a 3ds Max Daylight system.

Enabled – Turns on and off the sun light.

Intensity multiplier1 – An intensity multiplier for the VRaySun. Since the sun is very bright by default, you can use this parameter to reduce its effect. 

Size multiplier – Controls the visible size of the sun. This affects the appearance of the sun disc as seen by the camera and reflections, as well as the blurriness of the sun shadows. For more information, see The Size Multiplier Parameter example below.

Filter color – Changes the color of the sun and depends on the Color mode parameter.

Color mode – Affects the way the color in the Filter color parameter affects the color of the sun.

filter – Shifts the hue of the V-Ray Sun and Sky system towards the color specified in the Filter color field. 
direct
 – Sets the color of the V-Ray Sun to match the color in the Filter Color parameter. In this case the intensity of the light does not depend on the V-Ray Sun's position in the sky and is controlled through the intensity multiplier. 
override
 – Sets the color of the V-Ray Sun to match the color in the Filter Color parameter but the intensity of the light still depends on the V-Ray Sun's position in the sky.

 

 

 


 

Example: The Size Multiplier Parameter


This example demonstrates the effect of the Size multiplier parameter. Notice how changes in this parameter affect both the visible sun size and the shadow softness (however overall illumination strength remains the same).

Enabled: on, Turbidity: 3.0, Intensity multiplier: 0.01 

 

Size multiplier is 4.0

Size multiplier is 10.0

Size multiplier is 40.0

4
40

 


Sky Parameters


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

Hosek et al. – The VRaySky procedural texture is generated based on the Hosek et al. method.
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 cloudy sky.
PRG Clear Sky - The VRaySky procedural texture is generated based on the PRG Clear Sky method which has enhanced sunrise and sunset sky.

Ground albedo – Changes the color of the ground.

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

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).

Turbidity – Determines the amount of dust in the air and affects the color of the sun and sky. Smaller values produce a clear and blue sky and sun as you get in the country, while larger values make them yellow and orange as, for example, in a big city. For more information, see The Turbidity Parameter example below.

Ozone – Affects the color of the sun light. Available in the range between 0.0 and 1.0. Smaller values make the sunlight more yellow, larger values make it blue. For more information, see The Ozone Value example below.  

 

 

 


 

Example: The Turbidity Parameter


This example demonstrates the effect of the Turbidity parameter. Generally, this controls the amount of dust particles in the air. Notice how larger values cause the sun and the sky to become yellowish while smaller values make the sky clear.

Enabled: on, Intensity multiplier: 0.01, Size multiplier: 1.0 

 

Turbidity is 2.0

Turbidity is 4.0

Turbidity is 8.0

2
8

 

 


 

Example: Ozone Value

 

The Ozone parameter affects only the color of the light emitted by the sun. Higher values cause the color mapping mode to change. This example demonstrates the looks achieved with several different color mapping modes. See also the section on Color mapping for more details.

Enabled: on, Turbidity: 2.0, Intensity multiplier: 1.0, Size multiplier: 1.0. 

 

Ozone: 0.0

Ozone: 0.5

Ozone: 1.0

 

 

Options


Exclude – Excludes objects from illumination/shadow casting for the sun light.

Invisible – When enabled, makes the sun invisible, both to the camera and to reflections. This is useful to prevent bright speckles on glossy surfaces where a ray with low probability hits the extremely bright sun disk.

Affect diffuse – Determines whether the VRaySun is affecting the diffuse properties of the materials.

Affect specular – Determines whether the VRaySun is affecting the specular of the materials. The multiplier controls the suns contribution to specular reflections.

Affect atmospherics2 – Specifies whether the light influences the atmospheric effects in the scene. The value determines the amount of involvement.

Cast atmospheric shadows – When enabled, the atmospheric effects in the scene cast shadows.

 

 

Sampling


Shadow bias – Moves the shadow toward or away from the shadow-casting object (or objects). Higher values move the shadow toward the object(s), while lower values move it away. If this value is too extreme, shadows can "leak" through places they shouldn't or "detach" from an object. Other effects from extreme values include moire patterns, out-of-place dark areas on surfaces, and shadows not appearing at all in the rendering. For more information, see The Shadow Bias example below.  

Photon emit radius – Determines the radius of the area where photons would be shot. This area is represented by the green cylinder around the Sun's ray vector. This parameter has effect when photons are used in caustics. See the Photon Emission Radius example for more information.

 

 

 


 

Example: Shadow Bias


Enabled: on, Turbidity: 2.0, Intensity multiplier: 1.0, Size multiplier: 1.0. Notice how the shadows move towards the center of the render, that is towards the shadow casting object when the value is higher. 

 

Shadow Bias 0.0

Shadow Bias 7.0

Shadow Bias 15.0

Shadow Bias 30.0

 

 


 

Example: VRay Sun and Sky with Different Color Mapping Types

 

In addition to the parameters of the sun and sky, their appearance also depends on the selected color mapping mode. This example demonstrates the looks achieved with several different color mapping modes. See also the section on Color mapping for more details.

Enabled:  on,  Height Z:  800,  Turbidity:  3.0, Intensity multiplier: 0.01,  Size multiplier: 1.0

 

Color mapping: Exponential

Color mapping: HSV exponential

Color mapping: Intensity exponential

 

 

Clouds


Clouds on – Enables the cloud system.

Ground shadows – When disabled, the entire scene is covered by a single shadow or fully illuminated depending on whether the sun is blocked by a cloud at the current camera position. This is useful for smaller scenes and speeds up the rendering process. When enabled, V-Ray calculates the shadows precisely at every point of the scene. This provides a lot more definition to the shadows but may slow down the rendering process. It is helpful in larger scenes where the effect of the clouds is more visible. See the Clouds shadows example below.

Density – Controls the density of the cumulus and stratus types of clouds. A value of 1 fills up the sky with clouds. See the Clouds Density example below.

Density multiplier – A multiplier to the Density parameter. The larger the value, the darker the sky becomes at the horizon. Setting a value of 0 results in no clouds, regardless of the Density value.

Variety – Controls the variety of the cumulus and stratus types of clouds. See the Clouds Variety example below.

Seed – Generates a random value, based on the given number, to change the pattern of the clouds and the Contrails.

Cirrus amount – The maximum value of 1 fills the sky with cirrus clouds. Decreasing the value, lowers the presence of such clouds. When set to 0, the cirrus clouds are completely gone. See the Cirrus Amount example below.

Offset X (m) – Moves the cloud system by X axis. See the Clouds Offset example below.

Offset Y (m) – Moves the cloud system by Y axis. See the Clouds Offset example below.

Height (m) – Clouds position in height. See the Clouds Height example below.

Thickness (m) – Lower values make the cumulus and stratus types of clouds thin and sheer/lucent, while higher values make them full and heavy. See the Clouds Thickness example below.

Phase X (%) – Controls the phase by X axis, can be used to fine-tweak the cumulus and stratus clouds appearance. The appearance of the clouds loops at 0, 100, 200, etc. This parameter can be animated to resemble natural clouds appearance. See the How to add and animate clouds, without an HDRI example below.

Phase Y (%) – Controls the phase by Y axis, can be used to fine-tweak the cumulus and stratus clouds appearance. The appearance of the clouds loops at 0, 100, 200, etc. This parameter can be animated to resemble natural clouds appearance. See the How to add and animate clouds, without an HDRI example below.

Enable contrails – When enabled, plane contrails are simulated in the sky.

Number of contrails – Determines the number of contrails generated. See the Number of Contrails example below for more information.

Contrails strength – Determines the opacity of the contrails. Lower values create less opaque trails, which look older. See the Contrails Strength example below for more information.

Contrails distortion – Determines the amount of distortion in the contrails. See the Contrails Distortion example below for more details.

Contrails offset X/Y (m) – Offsets the contrails by a given value, according to the X or Y axis. See the Contrails Offset example below for more information.

Contrails time – Determines how far the contrails progress along the sky. See the Contrails time animation below for more details.

 

 


 

Example: How to add and animate clouds, without an HDRI

 

 

 


 

 

Example: Clouds Density

 

The Density parameter controls the amount of clouds in the sky. The higher the value, the higher the amount of clouds appearing in the render. 

Density = 0

Density = 0.4

Density = 0.8

Move the slider to see the example renders.

 

Example: Clouds Variety

 

This example shows the effect of the Variety parameter on the clouds' distribution and look.

Variety = 0

Variety = 0.5

Variety = 1

Move the slider to see the example renders.

 


 

Example: Clouds Shadows

 

 

This examples shows the effect of the Ground Shadows option.

 

off
on

 

 


 

Example: Cirrus Amount

 

This example shows how increasing the Cirrus Amount increases the appearance of the cirrus clouds in the render.

Cirrus amount = 0

Cirrus amount = 0.5

Cirrus amount = 1

Move the slider to see the example renders.

 

Example: Clouds Height

 

This example shows how the clouds change their position in the sky with increasing the Height value. 

Height = 500

Height = 1000

Height = 1500

Move the slider to see the example renders.

 


 

Example: Clouds Thickness

 

The Thickness parameter specifies how full the clouds are. Smaller values make them thinner and sheerer, while higher values make them look heavy. 

Thickness = 200

Thickness = 500

Thickness = 800

Move the slider to see the example renders.

 

Example: Clouds Offset

 

The following example demonstrates how changing the Offset X and Offset Y parameters affects the appearance of the clouds.

No offset

Offset X = -250, Offset Y = 0

Offset X = -250, Offset Y = 500

Move the slider to see the example renders.

 


Example: Number of Contrails

 

Note that the contrails are spread randomly across the sky. In most cases, the camera does not capture all of the contrails.

Number of contrails 5

Number of contrails 20

Number of contrails 40

5
40

Move the slider to see the example renders.

 

Example: Contrails Strength

 

This example shows how the strength parameter makes the contrails more visible and prominent in the sky.

Contrails strength 0.1

Contrails strength 0.5

Contrails strength 1.0

0.1
1.0

Move the slider to see the example renders.

 


Example: Contrails Distortion

 

The Contrails distortion parameter is used to achieve some variety in the trace line. Move the slider to see the example renders.

Contrails distortion 0.1

Contrails distortion 0.5

Contrails distortion 1.0

0.1
1.0

 

Example: Contrails Offset

 

The Contrails offset option introduces an offset along the X or Y direction in the sky. Move the slider to see the example renders.

Contrails offset X 0, Y 0

Contrails offset X 5000, Y 0

Contrails offset X 0, Y 5000

 


Example: Contrails Time

 

The frames in this animation show the Contrails time parameter with values ranging between 0 and 2.0, with a step of 0.2.

 

 

 

 

Notes


  1. By default, the VRaySun and VRaySky are very bright. In the real world, the average solar irradiance is about 1000 W/m^2 (see the references below). Since the image output in V-Ray is in W/m^2/sr, you will typically find that the average RGB values produces by the sun and the sky are about 200.0-300.0 units. This is quite correct from a physical point of view, but is not enough for a nice image. You can either use Color mapping to bring these values to a smaller range (which is the preferred way) or you can use the Sun intensity multiplier to make the sun and sky less bright. Using the VRayPhysicalCamera with suitable values also produces a correct result without changing the sun and sky parameters.
  2. The Affect atmospherics option has no effect on VRayAerialPerspective as this atmospheric effect only simulates volumetric appearance.

 


Here is a list of links and references about the V-Ray Sun and Sky implementation, as well as general information about the illumination of the Sun.

[1] A.J. Preetham, P. Shirley, and B. Smits, A Practical Analytic Model for Daylight, SIGGRAPH 1999, Computer Graphics Proceedings;
An online version can be found at http://www.cs.utah.edu/~shirley/papers/sunsky/ (Please note that this link is no longer valid)
This paper includes source code examples and is the base for the VRaySun and VRaySky plugins.

[2] R. H. B. Exell, The intensity of solar radiation, 2000
This page is available at http://www.jgsee.kmutt.ac.th/exell/IntensitySolarRad.pdf (Please note that this link is no longer valid).
This document contains information about the average intensity of the solar radiation, as well as some specific measurements.

[3] R. Cahalan, Sun & Earth Radiation
This page can be found at  http://climate.gsfc.nasa.gov/static/cahalan/Radiation/ (Please note that this link is no longer valid).
These pages contain a list of accurate solar irradiances across a large portion of the electromagnetic spectrum.

[4] D. Robinson-Boonstra, Venus Transit: Activity 3, Sun & Earth Day 2004
This document can be found online at 
http://sunearth.gsfc.nasa.gov/sunearthday/2004/2004images/VT_Activity3.pdf  (Please note that this link is no longer valid).
Among other things, this document gives the distance from the Sun to the Earth and the size of the Sun derived from astronomic observations.

[5] Hosek L, et al, An Analytic Model for Full Spectral Sky-Dome Radiance
This document can be found online at
http://cgg.mff.cuni.cz/projects/SkylightModelling/HosekWilkie_SkylightModel_SIGGRAPH2012_Preprint_lowres.pdf
Describes the Hosek sky model used by the VRaySun and VRaySky