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56 Chapter 17: Rendering
distribution. As with any statistical sampling
process, the greater the number of r ays u sed in
the approximation, the greater the accuracy of
the solution. During the initial quality stage,
the overall appearance of the lighting level of
thesceneisestablished. Theresultscanbe
interactively displayed in shaded viewports.
The initial quality stage performs repeated
passes, which are shown in the dialog’s progress
bar.
2. Refi ne Iterations (All Objects) and Refine
Iterations (Selected Objects)
Because of the random nature of the sampling
during the initial quality stage, some of the
smallersurfacesormeshelementsinthescene
mightmissbeinghitbyenoughrays(orany
rays at all). These sma ll surfaces remain dark,
and result in t he appearance of “variance” or
dark spots. To alleviate these art ifac ts, the
Refine stage “regathers light” at every surface
element.
You can perform the Refine stage for the entire
scene, or for selected objects in the scene.
3. Regathering
Even after the Refine stage, it is still possible
for visual artifacts to appea r in a scene because
of the topology of the original model. These
artifacts sometimes appear as shadow or light
“leaks.” To eliminate e ven these mo del-based
artifacts, a third, optional refinement stage
knownasPixelRegatheringoccursatthe
time of image rendering. This involves a final
“regather” process for each pixel of the image.
Regathering can add a considerable amount of
time to the rendering of a final image, but it also
produces the most detailed and ar tifact-f ree
images possible.
One benefit of using Regathering is that it
means the initial modeling and mesh resolution
don’t need to be nearly as “refined” or “tig ht”
as would otherwise be required.
R a dios it y Workf lows
The following sections describe how to set up a
scene for us e with radiosity.
Set Units Cor rectly B efor e Processi ng
Radiosity
For i mported geometry, you must m ake sure that
units are consistent in your scene b efore processing
radiosity(forexample,awallis8feethigh,not8
kilometers high). Units in 3ds Max must match
the units of the model because the radiosity engine
always uses an inverse s quare fal loff for lights.
Therefore, distance is crucial.
To make sure your units are setup correctly, use the
Units Setup dialog (page 3–891) .TheSceneUnit
is the most important unit in this dialog. This is
the unit that 3ds Max uses for its calculations. The
DisplayUnitisjustatoolthatletsyoucustomize
how units are displayed in the user interface.
Thefollowingtwoscenariosshowhowtosetunit
scales after importing geometry that has been
created using different units than what is cur rently
set in 3ds Max:
Example 1: You import a table that was created in
AutoCAD using metric scale. The table is 9 units
long, which corresponds to an actual length of
90 centimeters. When the table is imported into
3ds Max, it will measure 9 scene units. Therefore,
in the Units Setup dialog, you must set Scene Unit
Scale to 1 Unit= 10 centimeters. Your table is now
the correct units because it is 90 cent imeters long
in 3ds Max model.
Example 2: You have an AutoCAD model that
wascreatedusingArchitecturalUnits.Themodel
is a room measuring 20’-4” long. In AutoCAD,
Architectural Units are stored as inches. Therefore,
before importing the model to 3ds Max, make sure
to set the Scene Unit Scale to 1 Unit=1 inch. Once