William F Pokorny <ano### [at] anonymousorg> wrote:
>
> ...forgive me for using your scene as a lesson in how the
> POV-Ray pattern mechanisms work. Magic is fine until it acts against
> what you want to do.

Ha! Yes, certain values for the spline produce completely bland media. I have
since been trying to 'tease-out' an understanding of the spline's behavior, to
get *somewhat* more expected results.

>
> What you are seeing is the default wave modification code acting on the
> function values - before being using in a default map....
> [snip]

Thanks for the analysis. I'm not sure I understand the fine points yet, but as I
do more tests, things are becoming a bit clearer. And I completely forgot about
using my own color_map for the media; that adds even more 'art-like'
possibilities!

Yes, I finally started to realize that the color gradations and repetitions I
was seeing were due to a default 'ramp wave' behavior. As an experiment, I tried
triangle_wave and sine_wave instead (in the media density)-- which produce
additional interesting effects.

Meanwhile in official POV-ray, I have come up with at least two visually-based
'explanations' (rules?) about the spline/media interactions, that I am 99% sure
about:

1) The spline's index values correspond to the position and extent of 'blocks'
or 3-D cubes of media behavior-- with the blocks' patterns based in some way on
the vector values at those indices. I am still not sure *how* the vector values
are being interpreted though.

2) As the individual vector values go past 1.0, they start to produce what looks
like an increasing 'frequency' of the ramp wave behavior. This is sort of like
what Bald Eagle mentioned as being 'concentric shells'.

I am curious to know if this 'fits in' with your own analysis.

For the attached image examples-- and using an orthographic camera-- I modified
some of the scene values to produce a clearer understanding of what's going on.
The first image uses my original 3-D spline values; the second is a different
2-D variation.

(BTW, I also ran a moving-camera animation of my original scene; I might post
that to p.b.animations, just as an interesting if odd visual experiment.)

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