POV-Ray : Newsgroups : povray.advanced-users : Grid artifact in f_noise3d isosurface Server Time
16 Jun 2024 22:35:52 EDT (-0400)
  Grid artifact in f_noise3d isosurface (Message 40 to 49 of 49)  
<<< Previous 10 Messages Goto Initial 10 Messages
From: Warp
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 30 Jun 2002 17:17:20
Message: <3d1f7560@news.povray.org>
Alessandro Coppo <a.c### [at] iolit> wrote:
>>   Yes, they are. They must have too much spare time to wait.

> Well, when discussion sinks to this level, it is time to log out.

  From the page: "benchmarks now show the 100% pure Java matrix-matrix and
matrix-vector multiply running only about 2.5 times slower than the


  "Only"? Yes, the *do* have too much spare time. I don't.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -


Post a reply to this message

From:
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 02:02:12
Message: <n8g2ius42lc9e8uiggcg8ptksuss0ou3cm@4ax.com>
On Sun, 30 Jun 2002 22:34:14 +0200, Alessandro Coppo <a.c### [at] iolit> wrote:
> I did not fix any POV bug, I simply discorvered it and laughed about such 
> silly thing still laying around in a 10 years old program!

It is laying around becouse people prefer laughing than reporting. They prefer
free software without their possibility of help.

ABX


Post a reply to this message

From:
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 02:05:58
Message: <qdg2iuobc6jjs8p34lsds1j84ngmo4k8ej@4ax.com>
On Sun, 30 Jun 2002 22:43:52 +0200, Alessandro Coppo <a.c### [at] iolit> wrote:
> Just have a look at this URL:
>
> http://tilde-hoschek.home.cern.ch/~hoschek/colt/index.htm
>
> do you notice the domain? CERN...

domain doesn't say anything about author. java skills of one of the authors
are for example described at http://wwwinfo.cern.ch/support/java/utilities/:

  "I thing that it is a nice job, even though as a begginer in Java
  (I am using Java a few weeks only), I'm not quite sure that I've
  used the best way to do it."

ABX


Post a reply to this message

From: Philippe Debar
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 03:59:15
Message: <3D215CCA.4090300@wanadoo.be>

> It is laying around becouse people prefer laughing than reporting. They prefer
> free software without their possibility of help.


And maybe also because it wasn't visible before isosurfaces ?



Philippe


Post a reply to this message

From:
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 04:35:41
Message: <d9p2iukr9mf6n1iv1g0mqria0g3urbi5r8@4ax.com>
On Tue, 02 Jul 2002 09:56:58 +0200, Philippe Debar <phd### [at] wanadoobe> wrote:
> > It is laying around becouse people prefer laughing than reporting. They prefer
> > free software without their possibility of help.
>
> And maybe also because it wasn't visible before isosurfaces ?

Wasn't isosurfaces originally written for POV 2.2 ?

ABX


Post a reply to this message

From: Philippe Debar
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 09:50:20
Message: <3D21AF0C.3080409@wanadoo.be>

>>>It is laying around becouse people prefer laughing than reporting. They prefer
>>>free software without their possibility of help.
>>
>>And maybe also because it wasn't visible before isosurfaces ?
> 
> Wasn't isosurfaces originally written for POV 2.2 ?


Oops, yes... I forgot about that (I began to discover isosurfaces with 
Megapov...).


Anyway, the point I wanted to convey (I wonder why I always try the very 
roundabout way instead of writing what's on my mind...) is:
Why allow a lone laughing troll to depreciate your opinion of all free 
software users? The POV team itselfs, the Tag Team and most people on 
this news server (yourself included) is ample proof that many are ready 
to help :-)



Povingly,



Philippe


Post a reply to this message

From: Klaus Lehtonen
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 15:47:57
Message: <3d22036d@news.povray.org>
From: "Slime"
> At first I was a bit annoyed by this, but having looked at the 3.1 source
in
> the past, I know that it's caused by the way the noise functions are
> created. They are *based* on a grid pattern of random values, which are
> interpolated between. I'm not sure exactly how the new noise generator
> works, but since it shows the same artifact, I assume it's similar.

Is the interpolation cubic like in sp_lines or cosine based? (
http://freespace.virgin.net/hugo.elias/models/m_perlin.htm has decription of
the funtions that I'm writing) I tried to look at the source myself but my C
skills are pretty bad. If it is cosine based the grid could be natural part
of the function. I'm thinking this because the small lines that cause the
grid are visible even when using one dimentional version of the function.
(just change f_noise3d(x,y,z) to f_noise3d(x,0,0) ) Sorry if this is too
newbie question for advanced-users.

Klaus Lehtonen


Post a reply to this message

From: Christopher James Huff
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 2 Jul 2002 17:45:31
Message: <chrishuff-E851E1.16424602072002@netplex.aussie.org>
In article <3d22036d@news.povray.org>,
 "Klaus Lehtonen" <leh### [at] hotmailcom> wrote:

> Is the interpolation cubic like in sp_lines or cosine based? (
> http://freespace.virgin.net/hugo.elias/models/m_perlin.htm has decription of
> the funtions that I'm writing) I tried to look at the source myself but my C
> skills are pretty bad. If it is cosine based the grid could be natural part
> of the function. I'm thinking this because the small lines that cause the
> grid are visible even when using one dimentional version of the function.
> (just change f_noise3d(x,y,z) to f_noise3d(x,0,0) ) Sorry if this is too
> newbie question for advanced-users.

If I remember correctly, that page describes a very different algorithm 
than what is usually called "Perlin noise". It uses a bitmap filled with 
random values and then interpolated to get the basic noise, which is a 
very simple and direct way of doing it but doesn't give great results. 
The algorithm Ken Perlin came up with was quite different and more 
complex, I don't understand all of it and can't explain it here, but it 
doesn't rely on a 2D or 3D bitmap.

http://www.mrl.nyu.edu/~perlin/doc/oscar.html
http://students.vassar.edu/mazucker/code/perlin-noise-math-faq.html
http://www.threedgraphics.com/texsynth/

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/


Post a reply to this message

From: Klaus Lehtonen
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 4 Jul 2002 07:51:41
Message: <3d2436cd@news.povray.org>
"Christopher James Huff" <chr### [at] maccom>

> http://www.mrl.nyu.edu/~perlin/doc/oscar.html
> http://students.vassar.edu/mazucker/code/perlin-noise-math-faq.html
> http://www.threedgraphics.com/texsynth/

Thanks for the links. I think I understand what is causing the grid. I've
made a web page that explains it. http://koti.mbnet.fi/lehtkl/f_noise3d.htm
What do you think does this make some sense or am I just dreaming here?


Post a reply to this message

From: Philippe Debar
Subject: Re: Grid artifact in f_noise3d isosurface
Date: 4 Jul 2002 08:08:20
Message: <3D243A20.9000908@wanadoo.be>
Philippe Debar wrote:

>>OK, could you either post here or place on the site a short complete
>> sample
>>scene for at least the first image, please?
> 
> Done. Zipped scene file in p.beta-test.binaries. 
<snip>
> I will post the others soon,


e-hem... I did not... Would they be useful? If yes, I'll try to post 
them this week-end. If no, well...

Philippe


Post a reply to this message

<<< Previous 10 Messages Goto Initial 10 Messages

Copyright 2003-2023 Persistence of Vision Raytracer Pty. Ltd.