Workshop 8 Notes

COMPUTER AIDED ARCHITECTURAL DESIGN
Workshop 8 Notes, Week of October 16, 2016

Environment Settings, Sun, and Sky

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:

http://www.vray.com/vray_for_rhino/manual/

See especially sections 23. Environment and Lighting and 33. Sun and Sky. The dialog boxes from the above referenced manual are slightly outdated, but the methods suggested are revisited here with some variation and using a more up-to-date version of the software.

PART 1. Caustics, Indirect Caustics and Materials.

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

basic setup

2. Within the V-Ray Options dialog menu, go to the "Environment" tab, select the button labelled "m" under "Reflection/refraction (background), and add a "texSky" as per the techniques used in workshop 6 . Set the "Sky Model" to "Preetham et. al. Set "Turbity to 2.0.

3. Do a test rendering in V-Ray.

first rendering caustics off

4. 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.

basic render with caustics on

6. However, with the V-Ray materials editor create a white gray "standard" material named "plastic1" with a reflection layer. Set its diffuse color to light gray 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 andthe casted shadows to the earlier renderings but for the solid objects.

rerender with plastic 1

8. Now, however, within the V-Ray Options dialog box, go to the Indirect Illumination(GI) tab, and turn off the "on" check-box.

GI off

9. Re-render the image and note the higher contrast in comparison to the image under step 7.

renderingWithGI off

10. Turn back on Indirect Illumination, but also turn on the option for "Ambient Occlusion".

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 less flat.
ambient occusion rendering

12. Create a V-Ray material named "myGlass" with a light-gray color for diffuse color, for reflection color and for refraction color, per the techniques explored in workshop 8.

my glass

13. Re-render with the check-box for Indirect Illumination off.

render glass with caustics off

13. Returning to the Indirect Illumination(GI) tab, turn back on Caustics as well as Ambient Occlusion and re-render for greater contrast range result. 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.

glass with caustics and GI on

14. Within the V-Ray option editor, go to the "Environment" tab, set the GI Skylight color to yellow, and change the intensity to 4.0.

set gi skylight color to yellow

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

render GI Skylight set to yellow

Part II. Exploring texSky properties.

1. Return to the Reflection/refaction "textSky" map, and reset the "Sky Model" to "CIE Clear" and re-render.

setup texSky

2. 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.

cie clear rerender

3. Within the "Environment" tab, change the GI Skylight color from yellow to dark gray, and then return to the V-Ray texture editor for "texSky" and modify the following properties:

Water Vaper = 4.0
Turbidity = 4.0.
Ozone = 0.55

readjust tex sky

4. Rerender the model and the result is diffuse but a bit flatter than 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 for slighlty higher contrast.

restore GI skylight to black

6. Modify the sun position directly, approximating 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 environmental sky texture, 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: Gamma Correction

Gamma correction can be used to adjust for a display monitor making mid-tones appear darker than they should be.

1. Within the V-Ray Options editor, go to the Color mapping tab and set the Gamma and Input Gamma to 1.5 each:

reset gammat to 1.5

2. Re-render the last image from Part II.

rerender gama 1.5

3. Reset "Gamma" to 2.7 and" Input Gamma" to 2.7 and rerender. After re-adjusting the rendering through the "Color corrections" dialog box, the contrast range seems less flat:

rerender for gama at 207

Part IV: Viewing the Sun.

1. Return to the V-Ray texture editor, and reset the "texSky" size to 7.0.

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.

render sun

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\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 environment tab, and under Global Illumination (GI) select the letter "m" to re-enter the texture editor, change the type texture to "TextBitMap", go to the file load area at the top of the editor, and select one of the HDR files (e.g., CGSkies_0337_free.hdr). In addition, towards the right of the dialg box, adjust the Gamma number in conjunction with repeated selecting the preview button to ensure that the sky is relatively visible in the preview window. For example, in the dialog box box below, the "Gamma" number is set to 4.0. Finally, at the bottom of the dialog box, set the "UVW type" to "UVWGenEnvironment" and the "Mapping Type" to "Spherical":

select HDR file

2. Hit OK to return to the "Envronment" tab of the V-Ray options dialog box, set the intensity of the "Reflection/refraction(background)" to 27.0 or, after making test renderings, adjust the number to whatever intensity will be needed to ensure the visibilty of the sky.

set intensity

3. Similar to step 2, go to GI (skylight) and select the letter "m" to re-enter the texture editor. Change the type texture to "TextBitMap", and use the same settings used under part 2 for Reflection/refraction. Also, similar to step 2, adjacent to the "letter "m" in the "Environment" tab of the V-Ray option editor change the numerical value of 1.0 to 27.0.

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.