"Kirk Andrews" <kir### [at] tektonartcom> wrote:
> Using media in the water multiplied render times by ten--I am wondering if I
> could not get a sufficiently similar effect by using a ground fog translated
> below the water surface...?

Yes, media will tend to do that...

I don't think ground fog will do what you want for a few reasons.  First you
need to limit it to below the water surface.  Ground fog in POV doesn't have a
sharp upper limit, but rather continues to decrease as you go up.  I suppose
you could manipulate the properties so that it is virtually invisible above the
water surface.  Otherwise, you need to make the air above "solid" so that the
fog doesn't seep into it, this presents ior issues, plus having your camera
inside a non-hollow object.  Fog doesn't simulate the scattering effect that
gives tropical water it's colour.  It really neither scatters light nor absorbs
it, it just colours it.  Given this fact and the problems above, if you simply
want coloured water, use the interior attenuation instead (fade_distance etc).
You could also use just absorption media instead if you want a varying density
of the attenuation effects (this is a lot faster than scattering media).  If
you want actual added colour and not just absorption, use the negative filter
effect I stated before, or add emission media.  This will add colour to the
water without necessarily making it darker (even can make it brighter).  This
is a quick fix to simulate the real scattering effects, however, because it
isn't determined by it's actual interaction with light, it will appear
everywhere in the water giving it a glowing (or radioactive?) appearance.

You need to evaluate what effect you want, and which simulates it best in
cordination with acceptable render times.

-tgq

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