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'

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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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] gmxde>
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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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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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] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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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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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] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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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'