POV-Ray : Newsgroups : povray.bugreports : "mandel" as function in isosurface has unexpected results : [solved] "mandel" as function in isosurface has unexpected results Server Time
28 Mar 2023 16:37:21 EDT (-0400)
  [solved] "mandel" as function in isosurface has unexpected results  
From: Lars Rohwedder
Date: 16 Dec 2022 02:27:29
Message: <639c1de1@news.povray.org>
>> According to the documentation of isosurface, all points with
>> function value  < threshold are "inside" the isosurface object.
> Wellll...... it's an isoSURFACE, so there really is no inside, unless
> (IIRC) for csg you use all_intesections
>> The "mandel" pattern is "low" (near zero) far away from the
>> Mandelbrot set, increases slowly near the border of the set and is
>> 1 inside the "apple shape" set itself (with default values for
>> "interior" and "exterior".
> Can you cite that with a link, or is that your working hypothesis?


See the explanations for "interior" and "exterior" types 0 and 1.
A default color map is not mentioned there at all, hence I did not know
about that. :-/

>> So I had expected that a formula like 0.9 - mandel would give the
>> What went wrong here?
> Part of what's going wrong is that mandel is a POV-Ray pattern that
> has a built in color map.   And that wreaks hell with everything
> right from the beginning.

I see. It should be mentioned in the documentation of the mandel
pattern. :-/

> I'd say try using:
> #declare Mandel = function { pigment {mandel 1000 exterior 1, 1
> color_map {[0 rgb 0] [1 rgb 1]}}}
> But you're having more success than I am.

Thank you a lot! Changing the color map into a stupid black-to-white
ramp solves the problem.

See attached .pov files and renderings.

> Maybe you post your full scene as an attachment, and someone can
> figure this out.

I did it in my original posting.

Thanks again and enjoy the renderings (or use them as inspirations for
own "weird christmas tree" ideas. ;-)

Lars R.

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Download 'mandel.pov.txt' (2 KB) Download 'mandel.png' (145 KB) Download 'mandel2.pov.txt' (2 KB) Download 'mandel2.png' (201 KB)

Preview of image 'mandel.png'

Preview of image 'mandel2.png'


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