Autodesk LIGHTSCAPE, Manual

Page: 168 / 362

Daylight 10
160
Lightscape
not only calculating sunlight, but by calculating this
“skylight” as well.
The sky is modeled as a dome of infinite radii placed
around the scene. Skylight computes the illumina-
tion of a point in the scene with reference to all
directions around that point where the sky is visible.
The sky brightness is not constant over the sky
dome, but rather it changes depending upon the
position of the sun.
Skylight distribution is determined by the geograph-
ical location, time, and sky condition settings.
Using Daylight in Exterior
Models
The natural lighting of exterior scenes is handled
differently than interior scenes. With interior scenes,
very specific information about where natural light
is coming from (such as windows and openings)
may be taken into consideration to provide greater
accuracy and efficiency.
To simulate the effect of daylight on an exterior
scene, the entire sky dome is used when calculating
the illumination contribution from the sky.
Refining Shadows
You can set shadow casting for sunlight and skylight.
If you set these sources to not cast shadows, the
energy is distributed from the source to each surface
in its path as if there were no other surface blocking
it. However, when you disable shadow calculations,
sky illumination levels at a surface are determined by
the surface orientation. For example, all flat roofs in
a model of a city receive the same amount of illumi-
nation, regardless of the building height and the
surrounding buildings.
Typically, the shadows from direct sunlight are
important to your images. The subtle shadows
produced by the sky dome may not be as important,
depending on the level of quality required.
A great deal of processing is dedicated to the calcu-
lation of the shadows cast by the sky dome. If
shadows are not important in your model, you can
disable them and save substantial amounts of
processing time. However, the results will not be as
realistic.
Adjusting Shadow Accuracy
The illumination contribution from the sky is
computed by separating the sky dome into several
small sectors, which are treated as individual light
sources, and adding these sources together to get the
overall result. A higher accuracy setting results in a
greater number of sky sectors and slows down the
computation time.
To enable shadows cast by the sun and sky:
1.
Choose Light | Daylight.
The Daylight Setup dialog appears.
Room illuminated by sunlight and
skylight. Illumination around the windows
is greater than when only sunlight is used.