VRay for SketchUp Manual
Sun and Sky
The V-Ray Sun and Sky are based off
of research to accurately depict the sun and sky, which allows for easy
recreation of the Sun and Sky. They are intended to work together as well as
react to the angle and direction of the sun. In order to access to the sun
location, in the main menu click "Windows", select "Model Info", then select
"Location". This will allow you to select a location of the sun. You might
control the time and the day in the "Shadow Setting".
Using the Sun with the
V-Ray Physical Camera
In order to properly use the sun, it is a necessity that it be used in
conjunction with the Physical Camera. The Sun itself is extremely bright, and in
order to maintain the characteristics of the model, the sun must be kept close
to its correct intensity. To counteract the intense brightness of the sun it is
important to create a proper exposure of a scene with the physical camera. Using
the physical camera will also help accurately capture the correct colors of the
sky as well.
The properties of the sun in V-Ray for SketchUp are controlled in conjunction
with the Physical Sky properties under the Texture Editor for GI(Skylight) under
Environment render options. Here you will find many different controls which
change the appearance and affect of the sun. For right now we will maintain the
Exposing Your Scene with
the Physical Camera
Since the best way to make use of the Sun is to also use the physical camera,
access the V-Ray Options and in the Camera rollout enable the Physical Camera.
To determine the correct exposure you will need to do a quick render of the
image. If your image is too bright, or overexposed, then you will need to adjust
the F-stop, shutter speed, or ISO value to compensate. It maybe helpful to view
the color values in Float format, as this will help you determine the true
brightness of your image. This can be viewed by right-clicking and holding
anywhere in the frame.
The image below was rendered using the V-Ray Sun and the Physical Camera.
This image used the following values to achieve the correct exposure: F-Stop=
16, Shutter Speed= 300, ISO= 200.
|If you do not want to use the physical
camera it will be necessary to decrease the intensity of the sun by a
significant amount, however, the sun and sky may not act in the way it
Adding the V-Ray Sky
In V-Ray for SkechUp the Sky is added in the environment rollout of the V-Ray
options, click on the "m" next to GI parameters. You must have Indirect
Illumination enabled to access this, so enable it if you have not already.
Clicking the "m" should bring up the texture editor, and under Type select Sky.
At the top you will notice the option to select a light source, the SketchUp sun
is selected by default and VRay knows where the sun direction is coming from.
Lastly, there is an option next to the button that says Override Sun's
Parameters. This allows separate settings for the Sun and the Sky, but for
simplicity and continuity it is recommended to have this unchecked. Now go ahead
and repeat this process for the background. If we render again we'll notice that
our white ground plane has a slightly blue hue to it. This is due to the
influence of the sky on our scene.
of Day and the Sun’s appearance
Now that we have added the sun and sky, let’s see how the sun reacts to
changing the time of day. In order to change the position of the sun, simply
adjust the time of year and day using SketchUp Shadow Settings. (You can adjust
the location through SketchUp Model info). Now the appearance of the scene has
completely changed sole based on the position of our sun. This allows users the
flexibility to worry only about the time of day rather than adjusting the
appearance and intensity of the sun and the background.
Changing the Sun’s
Appearance with Turbidity
Although the time and position of the sun will have the most affect on the
appearance of the Sun and Sky, there are several other controls that will be
helpful in adjusting their appearance. Turbidity essentially changes the amount
of dust that is in the air. Values on the lower end or the spectrum will create
a very clear blue sky as you would see in the country side. Having larger values
will make the sky slightly yellow or orangish as you would see in the city.
Think of turbidity almost as a control for the haziness of the sky.
Changing the Sun’s Appearance with Ozone
The other useful parameter in adjusting the sun is Ozone. Ozone changes the
color of the sun itself from a slightly yellow tone to a slightly blue tone.
This can be very useful for fine adjustments to the appearance of the sun.
Gamma Correction and the
V-Ray Sun and Sky
Due to the physical nature of the sun and sky model it is intended to be
rendered using a gamma corrected linear workflow. Gamma correction compensates
for a monitor’s tendency to display mid-tones darker than they actually are.
Most programs embed the correction for this into the image, but because of the
nature of how V-Ray processes color information it does not correct for this.
Ultimately the result is that the VRay Sky will appear too dark if it is not
corrected for display on our monitors. Also if the image is not gamma corrected
the influence of the sky will not be accurate either. Needless to say, gamma
correction is very important, extremely so when using the V-Ray Sun and Sky.
The image on the left is has no gamma correction. This causes the sky to be
dark and its colors to be inaccurate. The image on the right has been gamma
corrected, which brightens the sky as well as having colors which accurately
represent the sky’s influence.
In order to gamma correct images both the inputs (textures and colors) and
output need to be adjusted. This is very quick and simple to do with V-Ray as
well as not impeding on workflow. In Global Switches, there is a section in the
bottom right corner containing the controls for gamma correction. To adjust the
inputs check Correct RGB and Correct LDR Textures. To adjust the output change
the Gamma value from 1 to 2.2