Workshop 9 Notes

COMPUTER AIDED ARCHITECTURAL DESIGN
Workshop 9 Notes, Week of October 12, 2020

Environment Settings, Sun, Sky, HDRI Images

There are a number of options availble for determining the the general atmosphere assocaited with rendering, light and shadows studies. Some documentation used to develop this tutorial are published on line in the vV-Ray for Rhino manual published on-line at:

https://docs.chaosgroup.com/display/VNFR/Lights

For more general on-line tutorials and reference materials on V-Ray see https://docs.chaosgroup.com/display/VNFR

PART 1. Caustics, Indirect Caustics and Materials.

1. Begin with 3 solid objects located on a V-Ray infinite plane and a V-Ray sun developed in Rhino similar to the methods illustrated in tutorial 8. Change the perspective view to an eye-level camera position so that the far edge of the infinite plane is visible in the view as a horizon line.

basic setup

2. Within the V-Ray Asset Editor, go to the "Environment" tab, select the checker-box icon adjacent to "Reflection/refraction (background), and add a "sky" as per the techniques used in workshop 6 . Set the "Sky Model" to "Preetham et. al. and set "Turbity to 2.0.
text sky preetham model

3. Do a test rendering in V-Ray and use the "Levels" option in the V-Ray frame buffer to adjust light balance.

initial rendering without materials assigned to objects

4. Now turn on the GI Skylight.

GI Skylight on

5. Select the checker box and then select the Sky option with the Preetham et. all. simlulation again similar to the method of workshop 6.

Add Preetham et. al. Sky to GI Skylight

6. Re-render the same view and note that the tone of the materials is a little warmer.

Add GI Skylight and re-render

7. Now, similarly again to workshop 6, activate the switch on "Refection", select the checker box, and add the Preetham et. al simulated Sun to it.

add reflection sky

8. Now create a neutral gray Generic material, name it "material_1" and apply it to the objects and ground plane.

add material 1

9. Re-render the same view and note the higher contrast range of the result.

add neutral gray material

9. Now go to the "Caustics" tab, and select the check-box for "Caustics" to turn caustics on.

turn on caustics

5. Do another test rendering in V-Ray. Given the lack of transparent surfaces there's very little difference if any between the two renderings.

rendering with caustics on

6. However, with the V-Ray materials editor create a light gray "generic " material named "reflection_1". Set the reflection color to white and and apply it to the three solid objects.

create plastic 1

7. Re-render the same perspective view with caustics on and note the basic similarity in terms of the overall lighting and the casted shadows to the earlier renderings but for the less flat appearance of the solid objects with a subtle hint of blue on the edge of the sphere and cone..

render relfection_1

8. Now, however, within the V-Ray Options dialog box, turn off the "on" check-box for "GI (Skylight)" and :Reflection"

GI off

9. Re-render the image and note the higher contrast in comparison to the image under step 7. Here, the overall rendering appears warmer and the contrast range is about the same. The contribution of the Sky illumination has been lowered and the proportion of direct sun color temperature to color appears to have been increased.

render GI Off

10. Turn back on the check boxes for "GI (Skylight)" and" Reflection", but also turn on the option for "Ambient Occlusion" on the right under "Global Ilumination" in the dialog box below.

ambient occlusions on

11. Re-render and note the higher contrast range on the sphere comparison with the images under steps 7 and 11. The overall impact appears to be slighlty softer and more diffuse. with still a hint of warm sun color temperature.

ambient occusion rendering

12. Create a V-Ray material named "glass_2" with a light-gray color for diffuse color, reflection color, refraction color and fog, per the techniques explored in workshop 7.

create glass 1

13. Apply "glass_1" to the sphere and re-render with "GI (Skylight)" and "Reflection" switched to off.

render glass with caustics off

14. Switch back on"GI (Skylight)" and "Reflection" and render again The rendering as a whole appears less flat. Note for example the greater difference in contrast between the shadows cast by the box and those cast by the sphere, and notice too the slighlty improved sharpness of the relflection on the cube and on the sphere

glass with caustics and GI on

15. Change the fog and reflection colors of "glass_1" to white and re-render.

$adjust refraction and fog$

Note that appart from the transparency of the sphere the overall intereflection of light is significantly changed.

$render adjusted fog and refraction$

16. Within the V-Ray option editor, go to the "Environment" tab, set the GI (Skylight) color to yellow, change the intensity to 4.0 and switch of the check-box for the Preetham et. al. simulatio on the right.

set gi skylight color to yellow

15. Re-render the image for a more distincly yellow tint to the overall rendering of surfaces.

rendered yellow skylight

Part II. Exploring texSky properties.

1. Return to the "Background", "GI(Skylight)" and "Background" skies, and reset the "Sky Model" to "CIE Clear".

change to CIE Clear

2. Set the color of the "GI (skylight)" back to the color black at inensity of 1. Re-render and note the difference with the last rendering of Part 1 with respect to the more solid blue color and less diffuse appearance of the background sky.

rendered CIE clear

3. Within the "Environment" tab, change the colors of the "Background", "GI (skylight)" and "Reflection" to dark gray at intensity 2.

adjust color to gray

Return to the properties of the"GI (skylight)" sky and modify the following properties:

Water Vaper = 4.0
Turbidity = 4.0.
Ozone = 0.55

This automatically adjusts the properties for "Background" and "Reflection" tp the same values.

readjust tex sky

4. Re-render the model and the result is diffuse but a flatter we obtained with the Preetham sky at the end of part 1.

adjusted turbidity, watervape and ozeon

5. Restore the GI (skylight) color back to black at intensity 1 for slighlty higher contrast.

restore GI skylight to black

6. Modify the sun position manually by selecting the sun directly from the model space and then going to the properties tab on the right hand side select the "Change Sun Angle" option .

change sun angle tool

That is, set the sunlight for morning, mid-day and late afternoon, and re-render accordingly:


morning	mid-day	late afternoon

Morning rendering with color adjusted via the "Color corrections" dialog box:

Mid-day rendeing with color adjusted via the "Color corrections" dialog box:

mid day rendering

Late afternoon rendering with color adjusted via the "Color corrections" dialog box:

7. Adjust the sunlight to approximate early afternoon.

Early Afternoon Sun Setting

8. Return to the CIE Sky, and change the turbidity to values of 2, 5 and 8 and also rendering in turn for each value respectively:

Turbidity = 2.0:

Turbidity = 4.0:

Turbidity = 8.0:

Part III: Viewing the Sun.

1. Return to the V-Ray Asset Editor,, Select the Light Iconr, and reset the "Sun Light " size to 7.0. Note that this more direclty accesses the same properties for "Background", "GI(Skylight)" and "Reflection" skies

Set Sim Size to 7

2. Change the Sun Azimuth to 220 and the Altitude to 20, and rotate the view so as to look in the approximate direction of the Sun, and render. This may take a number of trial renderings to pinpoint the location of the sunin the perspective view. Right-click on the view name "Perspective" in the upper-half hand corner fo the view, hold down the right-mouse button continuously and select the "Set Camera/Adjust Lens Length and Dolly" tool to adjust the view. Use this tool in combination with with the "Pan" tool to help find the appropriate adjustment of the view so the the sun will be visible within it.

view sun turbitity 8

3. Restore the Turbidity to 2.0 and re-render the same view.

sun with turbidity reset to 2.0

Part V: HDR Environmental Sky

Select an HDR ski from the classes\ARCH2710-Mark-FAL2020\examples\HDRSampleSkies, or download the entire folder, and place it in same folder as your Rhino 3dm file. A number of copyright free HDR skies are available on web sites for a fee and some are available without charge. These examples were obtained from the web site http://http://www.cgskies.com/ and subject to terms of restricted use for educational purposes. See the cgskies web site for copyright restrictions.

hdri sky

1. Go Back to the "V-Ray Asset Editor" and switch off the Environmental Overrides for "Background" , "GI(Skylight", "and "Refraction"

turn off overrides

2. Select the V-Ray lights tab and select the "Dome" light as well

lights tab

The "Dome" light is the fourth from the right-hand side:

dome light icon

Place the dome-light in the center of the model space and concurrently select the HDRI sky file. The dome light will orient the HDRI sky to the 3D model such that A rendering will produce the level of background illumination and lighting needed. However, the sky photo may include the sun itself. In this case, it may be necessary rotate the dome so that the sun is appropriately oriented to the model (e.g., placed along the negative y-axis).

place dome light

Optionally, select "Open" to return to Rhino. Using the scale tool, adjust the scale facor for the dome to a size that surrounds the model (500 was used in this case).

adjust scale dome light

3. Within the "V-Ray Asset Editor" select the "Dome Light" and adjust the scalar value for intensity to 1000.

edit dome light

Note that a more accurate approach is to specify the itensity in Lumens or Watts which is one of the pull down options. under "Units".

setting in watts

4. Change perspective as appropriate to establish a greater area of sky within the view, re-render, post-processing the result through the" Color corrections" dialog box as needed to obtain the appropriate exposure. See below renderings at 1000 scalar (center) and 14400 watts (right) with light levels adjusted in rendering.