8

1088 Glossary
squaremeterorcandelaspersquareinch. The
candela was orig inal ly defined as the luminous
intensity emitted by a single wax candle.
Finally, luminous intensity i s the light energy per
unit time emitted by a point source in a particular
direction. The unit of measure of luminous
intensity is the candela. Luminous intensity is
used to describe the directional distribution of a
light source, that is, to specif y how the luminous
intensity of a light source varies as a function of
the outgoing direction.
Because3dsMaxworkswiththesephysicallybased
photometric values, it can accurately simulate
real-world lighting and materials.
Photon M a p
A photon map™ is a technique to generate the
indirect illumination effects of
caustics (page
3–91)
and global illuminat ion (page 3–92) when
you render with the
mental ray renderer (page
3–77)
.Whenitcalculatesindirectillumination,
the mental ray renderer traces photons emitted
from a light. The photon is traced through the
scene, b e ing reflected or transmitted by objects,
until it strikes a diffuse surface. When it strikes a
surface, the photon is stored in the photon map.
Generating photon maps is time-consuming. To
improve performance, you must explicitly specify:
• Which lights emit photons for indirect
illumination.
• Which objects can generate caustics or global
illumination.
• Which objects can receive caustics or global
illumination.
The settings for generating and receiving caustics
are on the Object Properties dialog >
mental ray
Panel (page 1–121)
.
The photon map stores photons only for objects
that can receive caustics, global il lumination, or
both.
To further reduce the time required to generate a
photon map, photons are limited by trace depth
controls. Trace depth limits the number of times a
photon can be reflected, refracted, or both.
Inanimations,anotherwaytosavetimeistoreuse
the photon-map file. If lighting doesn’t change
over the course of an animation, calculate and
savethephoton-mapfileforthefirstframe,then
choose the Use Existing option for rendering
subsequent f r ames.
The mental ray renderer saves photon maps
as
PMAP files (page 3–1089) .Photonmap
controls are on the Render Scene Dialog >
Indirect Illumination panel >
Caustics And Global
Illuminat ion rollout (page 3–104)
.
PHY Files
Yo u c a n s a v e Phys ique (page 2–927) data to a
Physique (PHY) file. This saves data common to
allobjectsthatshareagivenPhysiquemodifier.
Later, you can reload the PHY file, either to restore
the data that belongs to a particular skin or portion
of skin, or to transfer the Ph ysique of one skin (or
portionofit)toadifferentone.
Physique
Physique (page 2–927) is a modifier that, when
applied to a mesh, allows the movements of
an underlying skeleton to seamlessly move the
mesh like bones and muscle under a human skin.
Physique will work on any point-based object,
including geometric primitives, editable meshes,
patch-based objects, NURBS, and FFD space
warps. It will attach to any skeleton structure,