Autodesk 24000-000000-9860 - Revit Architecture - PC, User Manual

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Indirect illumination
Indirect illumination simulates the interaction of light with the environment by bouncing light off surfaces,
including surfaces that are not directly exposed to a light source. If you increase the precision of indirect
illumination and the number of bounces, you can improve the smaller, subtle effects of lighting, and the
amount of light in a scene. However, increasing the amount of indirect illumination also increases the time
required to render the image. (In the Render Quality Settings dialog, use the Indirect Illumination options.
See
Render Quality Settings on page 1163.)
Section boxes and light groups
When you use section boxes to limit the geometry being rendered, you can significantly reduce the amount
of time required to render an image. (See
Defining the View Area to Render on page 1161.) You can also use
light groups to turn off lighting fixtures, thus reducing the number of lights that will impact the rendered
image. (See
Light Groups on page 1134. Remember, however, that lights that are not within the view can still
have a significant impact on the quality of the rendered image.) Section boxes exclude lights that are clipped.
When planned carefully and with forethought, the combined use of section boxes and light groups can
greatly reduce the amount of time required to render an image.
Render Performance and Materials
Materials simulate various effects such as reflections and textures. You specify the render appearance for
each material using the Materials dialog. (See
Changing the Render Appearance of a Material on page 465.)
When mental ray renders materials, its performance depends on the effects being simulated. In fact,
complicated render appearances for materials can slow down the rendering process more than complicated
geometry in the building model.
When preparing to render an image, consider the following.
How Colors and Patterns Affect Render Performance
The complexity and size of a color or pattern affect render speed. More complex patterns require the rendering
engine to calculate more samples so it can capture the details. The rendering engine works best when it can
identify areas of similar surface treatment and cam estimate appearances over large homogeneous areas.
For example, a smooth monochrome surface renders more quickly than a smooth patterned surface. A
large-scale pattern renders more quickly than a dense, intricate pattern. A detailed, perforated surface renders
more slowly than a simple surface.
The material render appearances that require the most time to render are (from slower to slowest): metallic
paint, flecked metal, hammered metal, water, frosted glass, and perforated metal. Slower render times for
these materials are proportional to how much of the scene they cover.
At the draft to medium quality settings, complicated materials may show many artifacts (small inaccuracies
or imperfections in the rendered image). Imperfectly reflective materials (such as wood floors and metal
mullions) appear speckled. These issues can be improved by adjusting the Blurred Reflection Precision value.
(See
Render Quality Settings on page 1163.)
To improve the appearance of patterned surfaces and silhouettes without significantly increasing render
time, adjust the Image Precision (Antialiasing) value. (See
Render Quality Settings on page 1163.) To produce
images with little lighting depth but crisp geometry, use the draft quality setting with a high value for Image
Precision (Antialiasing), such as 6.
1174 | Chapter 17 Rendering