POV-Ray : Newsgroups : povray.beta-test : Question on isosurface polarity keyword behavior. Server Time: 27 Jun 2017 06:59:00 GMT
  Question on isosurface polarity keyword behavior. (Message 1 to 3 of 3)  
From: William F Pokorny
Subject: Question on isosurface polarity keyword behavior.
Date: 8 Jan 2017 18:25:46
Message: <5872842a$1@news.povray.org>
I'm working up a potential pattern example for the distributed scenes 
collection and ran into a surprise where polarity is doing nothing and I 
expected it to. Perhaps I am confused as to intent?

There are two uses of it in the attached, working pattern.pov file. The 
first behaves as I expect, the second does nothing.

Is the second use supposed to work?

Bill P.


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Attachments:
Download 'potential.pov.txt' (4 KB)

From: clipka
Subject: Re: Question on isosurface polarity keyword behavior.
Date: 8 Jan 2017 20:06:39
Message: <58729bcf$1@news.povray.org>
Am 08.01.2017 um 19:25 schrieb William F Pokorny:
> I'm working up a potential pattern example for the distributed scenes
> collection and ran into a surprise where polarity is doing nothing and I
> expected it to. Perhaps I am confused as to intent?
> 
> There are two uses of it in the attached, working pattern.pov file. The
> first behaves as I expect, the second does nothing.
> 
> Is the second use supposed to work?

In the second case, you're not using the actual isosurface, just its
potential.

The "polarity" keyword does /not/ affect the underlying potential, and
hence it also does not affect the resulting potential pattern. It just
affects which portion of the isosurface is considered inside, and which
one is considered outside:

By default, the "inside" of an isosurface is the set of all points
(inside the contained_by shape) where the potential is _smaller_ than
the threshold.

The "inside" of an isosurface with a positive "polarity" setting, on the
other hand, is the set of all points (inside the contained_by shape)
where the potential is _larger_ than the threshold (making the behaviour
consistent with blobs).


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From: William F Pokorny
Subject: Re: Question on isosurface polarity keyword behavior.
Date: 8 Jan 2017 20:39:00
Message: <5872a364$1@news.povray.org>
On 01/08/2017 03:06 PM, clipka wrote:
> Am 08.01.2017 um 19:25 schrieb William F Pokorny:
>
> In the second case, you're not using the actual isosurface, just its
> potential.
>
> The "polarity" keyword does /not/ affect the underlying potential, and
> hence it also does not affect the resulting potential pattern. It just
> affects which portion of the isosurface is considered inside, and which
> one is considered outside:
>
> By default, the "inside" of an isosurface is the set of all points
> (inside the contained_by shape) where the potential is _smaller_ than
> the threshold.
>
> The "inside" of an isosurface with a positive "polarity" setting, on the
> other hand, is the set of all points (inside the contained_by shape)
> where the potential is _larger_ than the threshold (making the behaviour
> consistent with blobs).
>
Thank you Christoph, I was indeed thinking polarity >0 flipped the 
underlying potential.

Bill P.


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