Autodesk LIGHTSCAPE, Manual

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Introduction 1
2
Lightscape
specific photometric files directly from lighting
manufacturers. You can also specify natural daylight
simply by indicating the location, date, and time of
day.
Interactivity
The result of a radiosity solution is not just a single
image but a full 3D representation of the light distri-
bution in an environment. Because the lighting is
precalculated, Lightscape can display specific views
of a fully rendered model much faster than with
traditional computer graphics techniques. With
faster hardware, it is often possible to move interac-
tively through rendered environments. High-quality
walkthrough animations for film or video can be
generated in a fraction of the time required with
other professional animation systems.
Progressive Refinement
Unlike other techniques, a Lightscape solution
provides instant visual feedback, which continues to
improve in quality over time. At any stage in the
process, you can alter a surface material or lighting
parameter and the system will compensate and
display the results without starting the process over.
The progressive refinement radiosity algorithms
implemented in Lightscape give you precise control
over the quality of visualization required to perform
any given design or production task.
Computer Graphics Rendering
This section provides an overview of computer
graphics rendering and a conceptual understanding
of the techniques available with Lightscape. This
information will help you decide which technique is
most suitable for the visualization task you want to
perform.
A 3D model contains geometric data defined in rela-
tionship to a 3D Cartesian coordinate system. This
system is sometimes referred to as
world space . The
model may also contain other information about the
material of each object and the lighting. The image
on a computer monitor is made up of a large number
of illuminated dots called
pixels . The task in creating
a computer graphics image of a geometric model is
to determine the color for each pixel on the screen
(screen space) based on the model information and a
specific viewpoint.
The color of any specific point on a surface in a
model is a function of the physical material proper-
ties of that surface and the light that illuminates it.
Two general
shading algorithms —local illumination
and global illumination—are used to describe how
surfaces reflect and transmit light.
Local Illumination
Local illumination algorithms describe how indi-
vidual surfaces reflect or transmit light. Given a
description of light arriving at a surface, these math-
ematical algorithms predict the intensity, spectral
character (color), and distribution of the light
leaving that surface. The next task is to determine
where the light arriving at the surface originates. A
simple rendering algorithm considers only the light
coming directly from the light sources themselves in
the shading.
Global Illumination
In considering more accurate images, however, it is
important to take into account not only the light
sources themselves, but also how all the surfaces and
objects in the environment interact with the light.
For example, some surfaces block light, casting
shadows on other surfaces; some surfaces are shiny,
in which case we see in them the reflections of other
surfaces; some surfaces are transparent, in which