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58 Chapter 17: Rendering
imported to 3ds Max, the room will measure 244
units long (20’*12+4”).
Tip: Use the Measure Distance tool (page 2–15) to
quickly check dimensions in 3ds Max.
Physically B ased Work flow
Use radiosity (page 3–51) to create ph ysically based
lighting simulations. When doing so, keep in m ind
the followi ng:
• Scene dimensions: Make sure your scenes are
accurately dimensioned, with consistent units
(a light bulb in a room 120 meters high would
look a lot different than it would in a room 120
inches high).
• Lights : Yo u s h o u l d w o r k e x c l u s i v e l y w i t h
Photometric lights (page 2–1301). You should
also ma ke sure that the lig ht intensities are
within a normal range.
• Natural Lighting: To simulate natural light,
you should only use IES sun (page 2–1309) and
IES Sky (page 2–1312).Theseprovideaccurate
photometric representations of sunlight and
skylight based on a specified location, date and
time.
• Materi a l Reflecta nce: You should ensure that
thematerialsyouuseinyourscenehavea
reflectance value (page 2–1430) within the range
of the physical materials they represent. For
example, a painted white wall should have a
maximum reflectance of approxim ately 80%;
however, a pure white color material (RGB:255,
255, 255) would have a reflectance of 100%.
This means that the material reflects 100% of
the energy received.
• Exp osur e Cont r ol : Theexposurecontrolisthe
equivalent of the aperture of a camera. Make
sureyouenabletheexposurecontrolandseta
value that prov ides the final results you desire.
To process radiosity for photometric lights using a
physically based work flow:
1.
Ensure that your geometry is set to a physically
correct scale and that the materials have val id
reflectance values.
2. Place photometric lights in your scene. The
benefitofthisworkflowisthatitallowsyou
to place lights in your scene the same way you
would in the real world. You can create new
photometric lig hts or, using t he asset browser
(page 3–504),draganddroppresetluminaire
objects (page 1–111) from the included librar y.
Yo u c a n a l s o r e f e r t o Common Lamp Values
(page 2–1329).
3. Choose Rendering > Environment to display
the Environment panel (page 3–272).Select
thetypeofexposurecontrolyouwanttouse
(typically Logarithmic (page 3–297)).
4. Click Render Scene to preview the
lighting. At this stage, the radiosity will not be
processed but you can quick ly confirm that the
direct lighting is correct. Adjust the position
of the lig hts if desired.
5. Choose Rendering > Advanced Lighting >
Radiosity. Make sure that Active is turned on.
6. On the Radiosity Parameters rollout, click
Start to process radiosit y. Once the Radiosity
calculation has been completed, you should
see your results in the viewports. The light
levels are stored with the geometry and you
can interactively navigate around the model
without reprocessing the scene.
7. Click Render Scene again. The renderer
will calculate the direct lighting and shadows,
and the radios ity solution (indirect lighting)
will be integrated as a modulated ambient light.