"Ron Parker" <ron### [at] povrayorg> wrote:

> It really can be argued both ways, but those who would argue that the
> density factor should scale with the container have a difficult question
> to answer: how should it scale when the container is scaled nonuniformly?
> 
> 
> 
If you think of media as tiny emitting/absorbing/reflecting particles in the
container's volume (which is what it is supposed to model) there are only
two possible ways to handle scaling the container AFAICS.

The current method is to keep constant the "number of particles" per unit of
volume. Thus if you scale the container, the total number of media particles
in the container changes and thus the apparent opacity changes. Frankly, I
think this is perfecly logical and in no way inferior to the alternative.

The other possible approach, the one which people seem to be talking about
here, is to keep constant the "number of media particles" in the container,
irrespective of scaling. Obviously this only gives the result people expect
if the container is scaled uniformly. Anyway, the correct conversion should
be something like:

Mult=sqrt(3)/vlength(Scale)

where Scale is the scaling vector of the container, and Mult is the
multiplier to be applied to the media density in the scaled container.

Since it only keeps the apparent opacity if the scaling is uniform, I'm not
sure it would be such a good default. People would then probably expect the
opacity to always stay the same, and it would be even harder to explain to
them why this is not the case with non-uniform scaling.

-- 
Margus Ramst

Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg
Home page http://www.hot.ee/margusrt

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