Quick guide to media (using Moray's material editor)

Moray, being made for POV 3.1, doesn't have the new
sampling methods for media, so that won't be covered.

Moray's material editor allows you to create materials
with a tree-like interface, with the parts having their
value boxes.

The [interior] section has the IOR, Caustics, and Fade
values, and one (or more) [media].

The [media] is composed of Intervals (default is 10,
lowering it speeds up media calculation), Sampling
(default is min 1, max 1, increasing them slows down
media calculations).  Next are Confidence, Variance,
and Ratio.  Low confidence and high variance are
fast but not realistic, high confidence and low
variance are incredibly slow but realistic.  Ratio
I have no freakin' idea what it's for, or what effect
it has on the media.  I have it set at 0.5 in most of
my stuff.  Increasing intervals also increases 'realism'.

The Scattering portion is where things get tricky,
especially if you camera is inside the scattering media.
Type of scattering is 1 (isotropic), 2 (mie hazy), 3
(mie murky), 4 (rayleigh), 5 (henyey-greenstein).  It
does make a difference which one you pick as to the
appearance of your media-filled object.  H-G scattering
has an eccentricity value.  There is also an Extinction
value, which gives a fog-like effect.

The [emission color] is the colour the media adds to
light passing through it, [absorbtion color] is sub-
tracted from the light passing through, and scattering
colour is the colour applied to the beam of light
itself.  [density] is the pattern of 'particulate
matter' in the scattering media; these are AFAICT
wildly unprecdictable if you change from one to another
if the camera is inside the media, but have the same
values in all other sections.  Spherical works best
in most cases, but cylindrical or planar can also have
predictable results.  (Planar can be funky at times tho,
but in a good way).  The density can be transformed and
noisified and warped, but, again, do so without a goal.

When the camera is inside the media, most of the values
for emission, absorbtion, and scattering produce useless
results.

Moray's Material Editor is a good way for coarse tuning
of media, since it renders a simple primitive against
an optional floor/wall, so you don't need to spend 5
hours rendering a scene only to discover you want to
change this or that value in the media.

So it is said, so it is written.  Amen.
-- 
Tim Cook
http://empyrean.scifi-fantasy.com
mirror: http://personal.lig.bellsouth.net/lig/z/9/z993126

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