On 2/26/22 22:18, Kenneth wrote:
> 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.)
> 

I'm interested in seeing the animation.

I like too your images. You dug much deeper into what the actual values 
back from the function (spline) were in relation to image than did I. I 
thought only about the rough ranges of values.

Rules look good to me(1).

Bill P.

(1) - Lesser quirks and detail to be had - especially in the official 
POV-Ray code - but another day...

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