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Been playing with isosurfaces in 3.5 and I am wondering
if the attached image is a bug or not. It happens using
f_noise3d and with f_noise_generator using generator 0 or 1.
Using f_noise_generator with a generator of 2 does not produce
the problem.
.pov source posted on povray.scenes.text-files
Pete
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Attachments:
Download 'iso35_01.jpg' (14 KB)
Preview of image 'iso35_01.jpg'
![iso35_01.jpg](/povray.binaries.images/attachment/%3C3bbce60b.1409922%40localhost%3E/iso35_01.jpg?ttop=443840&toff=10350&preview=1)
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In article <3bbce60b.1409922@localhost>, PeterC@nym.alias.net.almost
says...
> Been playing with isosurfaces in 3.5 and I am wondering
> if the attached image is a bug or not.
This is a typical problem resulting from an insufficient max_gradient.
Not a bug.
Lutz-Peter
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From: Christoph Hormann
Subject: Re: is this a bug? (~14k) - iso35_01.jpg (1/1)
Date: 5 Oct 2001 02:20:42
Message: <3BBD520F.DA8D9449@gmx.de>
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nospam wrote:
>
> Been playing with isosurfaces in 3.5 and I am wondering
> if the attached image is a bug or not. It happens using
> f_noise3d and with f_noise_generator using generator 0 or 1.
> Using f_noise_generator with a generator of 2 does not produce
> the problem.
> .pov source posted on povray.scenes.text-files
>
Sorry, but sometimes i wonder why we put much work into the documentation
if it's not read.
Reading the corresponding chapters from the docs when working on a new
feature is really a good idea, nearly everytime i read a chapter i
recognize something new or what i forgot.
Christoph
--
Christoph Hormann <chr### [at] gmx de>
IsoWood include, radiosity tutorial, TransSkin and other
things on: http://www.schunter.etc.tu-bs.de/~chris/
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hmmm looks like a silhouette of a phoenix
nospam wrote:
> Been playing with isosurfaces in 3.5 and I am wondering
> if the attached image is a bug or not. It happens using
> f_noise3d and with f_noise_generator using generator 0 or 1.
> Using f_noise_generator with a generator of 2 does not produce
> the problem.
> .pov source posted on povray.scenes.text-files
>
> Pete
>
> [Image]
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http://www.students.tut.fi/~warp/povVFAQ/languageVFAQ.html#isosurfacebug
--
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}// - Warp -
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From: Marc-Hendrik Bremer
Subject: Re: is this a bug? (~14k) - iso35_01.jpg (1/1)
Date: 5 Oct 2001 12:02:18
Message: <3bbdd98a@news.povray.org>
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Warp schrieb in Nachricht <3bbdba92@news.povray.org>...
>http://www.students.tut.fi/~warp/povVFAQ/languageVFAQ.html#isosurfacebug
>
Wouldn't it be good to mention "accuracy" in this VFAQ-Answer, too?
Marc-Hendrik
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From: Christoph Hormann
Subject: Re: is this a bug? (~14k) - iso35_01.jpg (1/1)
Date: 5 Oct 2001 12:53:27
Message: <3BBDE65F.62377969@gmx.de>
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Marc-Hendrik Bremer wrote:
>
> Wouldn't it be good to mention "accuracy" in this VFAQ-Answer, too?
>
For what reason? I don't remember many people having problems with that,
and the meaning is pretty self explanatory.
Christoph
--
Christoph Hormann <chr### [at] gmx de>
IsoWood include, radiosity tutorial, TransSkin and other
things on: http://www.schunter.etc.tu-bs.de/~chris/
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From: Marc-Hendrik Bremer
Subject: Re: is this a bug? (~14k) - iso35_01.jpg (1/1)
Date: 5 Oct 2001 14:07:12
Message: <3bbdf6d0@news.povray.org>
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Christoph Hormann schrieb in Nachricht <3BBDE65F.62377969@gmx.de>...
>Marc-Hendrik Bremer wrote:
>>
>> Wouldn't it be good to mention "accuracy" in this VFAQ-Answer, too?
>>
>
>For what reason? I don't remember many people having problems with that,
>and the meaning is pretty self explanatory.
Because in my opinion those artefacts are not always caused by an inaccurate
max_gradient. Esp. those where big parts are missing or disappearing seems
to me more like an inaccurate accuracy then a max_gradient problem (which
are those black spots like in the scene the thread started with). I may be
wrong in this, but that's how I experienced it in the past.
In addition max_gradient and accuracy seems not to be independent if I
remember an article of the original isosurface-patch writer some weeks ago
correct (unfortunately it was in one of those "Hey folks!"-threats and I
can't find it). While max-gradient seems to determine the "step-width" of
the algorithm, accuracy tells when to stop to look for an ray-intersection.
Is this wrong?
Of course, max-gradient is far more often the problem, which leads to those
artefacts.
Marc-Hendrik
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From: Christoph Hormann
Subject: Re: is this a bug? (~14k) - iso35_01.jpg (1/1)
Date: 5 Oct 2001 15:17:35
Message: <3BBE0827.BE2E41F3@gmx.de>
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Marc-Hendrik Bremer wrote:
>
> Because in my opinion those artefacts are not always caused by an inaccurate
> max_gradient. Esp. those where big parts are missing or disappearing seems
> to me more like an inaccurate accuracy then a max_gradient problem (which
> are those black spots like in the scene the thread started with). I may be
> wrong in this, but that's how I experienced it in the past.
Accuracy just influences how small details are visible, lower values lead
to more detailed surfaces and usually require higher max_gradient. Just
try it, the default value of 0.001 is quite low, if you use for example
0.1 on a RMF function isosurface, you will get a not very detailed
surface.
Christoph
--
Christoph Hormann <chr### [at] gmx de>
IsoWood include, radiosity tutorial, TransSkin and other
things on: http://www.schunter.etc.tu-bs.de/~chris/
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From: Marc-Hendrik Bremer
Subject: Re: is this a bug? (~14k) - iso35_01.jpg (1/1)
Date: 5 Oct 2001 16:27:24
Message: <3bbe17ac@news.povray.org>
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Christoph Hormann schrieb in Nachricht <3BBE0827.BE2E41F3@gmx.de>...
>Accuracy just influences how small details are visible, lower values lead
>to more detailed surfaces and usually require higher max_gradient. Just
>try it, the default value of 0.001 is quite low, if you use for example
>0.1 on a RMF function isosurface, you will get a not very detailed
>surface.
>
While you are right that higher accuracy values decrease the level of
detail, it has other influences, too.
I just tried it with an old scene and attached the resulting image. I
increased the accuracy value by far (0.1 instead of 0.000001) and left
anything else the way it was (after converting to 3.5 language of course).
Pov reports, that I should decrease max_gradient to lower rentertime (5.141
instead of 6). In my opinion that black part is one of those isosurface
artefacts.
Marc-Hendrik
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Attachments:
Download 'landschaft low acc.jpg' (12 KB)
Preview of image 'landschaft low acc.jpg'
![landschaft low acc.jpg](/povray.binaries.images/attachment/%3C3bbe17ac%40news.povray.org%3E/landschaft%20low%20acc.jpg?ttop=443840&toff=10350&preview=1)
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