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The perlin-noise function itself has got nothing to do with fractals
(correct me if I'm wrong :-)
You get something that's called "Fractal Brownian Motion" (FBM) when you
add "turbulence" to the pigment. The POV-Documentation explains how
turbulence works.
-Sascha
Andrew Coppin wrote:
> A fairly good introduction can be found on:
>
> http://freespace.virgin.net/hugo.elias/models/m_perlin.htm
>
>
> Thanks. This was helpful.
>
> So, essentially, the Perlin noise function is built on a normal random
> function where a point (in whatever dimensionallity of space) is the seed,
> yielding the randomness between distant points. Then interpolation is used
> to make points nearby have similar values. Oh, and the fractal bit - several
> different interpolated random functions of different wavelengths and
> amplitudes are added together for extra "natralness". Is that about how it
> works?
>
> Andrew.
>
>
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sascha wrote:
>
> You get something that's called "Fractal Brownian Motion" (FBM) when you
> add "turbulence" to the pigment. The POV-Documentation explains how
> turbulence works.
'fBm' stands for 'fractional Brownian motion'.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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You're right, of course.
Christoph Hormann wrote:
>
> sascha wrote:
>
>>You get something that's called "Fractal Brownian Motion" (FBM) when you
>>add "turbulence" to the pigment. The POV-Documentation explains how
>>turbulence works.
>
>
> 'fBm' stands for 'fractional Brownian motion'.
>
> Christoph
>
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On Sat, 10 May 2003 19:06:21 +0200, sascha
<sas### [at] users sourceforge net> wrote:
>The perlin-noise function itself has got nothing to do with fractals
>(correct me if I'm wrong :-)
I think what "fractal" stands for in this context is that is
inherently self-similar in different scales (to a limited extent
though, unlike "true" fractals)
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vip bg
TAG e-mail : pet### [at] tag povray org
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Peter Popov <pet### [at] vip bg> wrote:
> I think what "fractal" stands for in this context is that is
> inherently self-similar in different scales (to a limited extent
> though, unlike "true" fractals)
No, the word "fractal" does not imply self-similarity. The origin of
the word is related to mathematical calculations of the dimensions of
a fractal shape, which is fractional in a mathematical sense.
--
#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 -
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In article <3ebf872c@news.povray.org>, Warp <war### [at] tag povray org>
wrote:
> No, the word "fractal" does not imply self-similarity. The origin of
> the word is related to mathematical calculations of the dimensions of
> a fractal shape, which is fractional in a mathematical sense.
Actually, it has nothing to do with that. The words "fractal" and
"fraction" have a common root, but "fractal" is more closely related to
"fractured" and "fragment". Mandelbrot coined the word "fractal" from
the Latin "fractus", which means rough, irregular, or broken, and it
does refer to the self-similarity aspect: if you were to break a fractal
into pieces ("fracts"?), each fragment would appear similar to the
others.
Here's a quote from Mandelbrot himself: "I coined fractal from the Latin
adjective fractus. The corresponding Latin verb fragere means 'to
break': to create irregular fragments...how appropriate for our needs!"
--
Christopher James Huff <cja### [at] earthlink net>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tag povray org
http://tag.povray.org/
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In article <q7lubvcvspu6h4f1sabho2niej44dcp26q@4ax.com>,
Peter Popov <pet### [at] vip bg> wrote:
> >The perlin-noise function itself has got nothing to do with fractals
> >(correct me if I'm wrong :-)
>
> I think what "fractal" stands for in this context is that is
> inherently self-similar in different scales (to a limited extent
> though, unlike "true" fractals)
Perlin noise is not self-similar at different scales, though. It is
self-similar at one scale only.
Now, things like sum 1/F-noise are fractal. (wrinkles, granite)
http://astronomy.swin.edu.au/~pbourke/texture/perlin/
--
Christopher James Huff <cja### [at] earthlink net>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tag povray org
http://tag.povray.org/
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Oh no... don't tell me I've inadvertantly started a "what is a fractal" holy
war... *wink*
Andrew.
(Let's just accept that there is no accepted definition ;-)
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Andrew Coppin <orp### [at] btinternet com> wrote:
> (Let's just accept that there is no accepted definition ;-)
I think that's a wrong statement.
--
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -
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On Mon, 12 May 2003 12:20:45 -0400, Christopher James Huff
<cja### [at] earthlink net> wrote:
>Perlin noise is not self-similar at different scales, though. It is
>self-similar at one scale only.
>Now, things like sum 1/F-noise are fractal. (wrinkles, granite)
You're right, of course. Perhaps I should have specified that some of
the patterns in POV that implement Perlin noise use it in 1/F fractal
noise implementations. Nitpick :)
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vip bg
TAG e-mail : pet### [at] tag povray org
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