POV-Ray : Newsgroups : povray.general : is this bug or floating point error (noise on torus) Server Time: 25 Sep 2017 15:08:35 GMT
  is this bug or floating point error (noise on torus) (Message 1 to 9 of 9)  
From: Wlodzimierz ABX Skiba
Subject: is this bug or floating point error (noise on torus)
Date: 9 Mar 2001 15:40:37
Message: <3aa8f975@news.povray.org>
Currently I play a lot with orthographic camera.
I found that going away with location of camera makes torus very strange.
There is sentence in docu that "If the torus renders improperly you may add the
keyword sturm to use POV-Ray's slower-yet-more-accurate Sturmian root solver."
(btw. this is in "torus" section - but in section "sturm" there is no torus on
the list).
Well, I have added this keyword and IMO without result. This apperar in POV-Ray
3.1g for Windows on WinNT4 with 128 MB and with MegaPOV 0.7 on the same machine.
Run below code with S=1,10 and 100.

#declare S=1; /* 1,10,100 */
camera{orthographic location -(10*S)*z direction z right x up y*3/4
look_at -9*z}
light_source{<-30, 30, -30> color rgb 1 translate <-30, 30, -30>}
torus{.1 .04 /*sturm*/ texture{pigment{color rgb 0.5}}}

ABX


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From: Josh English
Subject: Re: is this bug or floating point error (noise on torus)
Date: 9 Mar 2001 20:00:20
Message: <3AA936C4.ABEBA933@spiritone.com>
I tried it, and at S=100, it was gone. I started to get grainy at S=15. So I was 150
units away looking at something with an vertical angle of  0.015278874  it's tangent
is 0.000266666. This is pretty small, but I can't imagine the computers cutoff being
so high.

Josh

Wlodzimierz ABX Skiba wrote:

> Currently I play a lot with orthographic camera.
> I found that going away with location of camera makes torus very strange.
> There is sentence in docu that "If the torus renders improperly you may add the
> keyword sturm to use POV-Ray's slower-yet-more-accurate Sturmian root solver."
> (btw. this is in "torus" section - but in section "sturm" there is no torus on
> the list).
> Well, I have added this keyword and IMO without result. This apperar in POV-Ray
> 3.1g for Windows on WinNT4 with 128 MB and with MegaPOV 0.7 on the same machine.
> Run below code with S=1,10 and 100.
>
> #declare S=1; /* 1,10,100 */
> camera{orthographic location -(10*S)*z direction z right x up y*3/4
> look_at -9*z}
> light_source{<-30, 30, -30> color rgb 1 translate <-30, 30, -30>}
> torus{.1 .04 /*sturm*/ texture{pigment{color rgb 0.5}}}
>
> ABX

--
Josh English -- Lexiphanic Lethomaniac
eng### [at] spiritonecom
The POV-Ray Cyclopedia http://www.spiritone.com/~english/cyclopedia/
"He who hebetates is last."


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From: Ron Parker
Subject: Re: is this bug or floating point error (noise on torus)
Date: 9 Mar 2001 20:41:08
Message: <slrn9aifv7.b89.ron.parker@fwi.com>
On Fri, 09 Mar 2001 12:02:12 -0800, Josh English wrote:
>I tried it, and at S=100, it was gone. I started to get grainy at S=15. So I was 150
>units away looking at something with an vertical angle of  0.015278874  it's tangent
>is 0.000266666. This is pretty small, but I can't imagine the computers cutoff being
>so high.

I wonder if it has anything to do with the definition of EPSILON. 

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.


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From: Ken
Subject: Re: is this bug or floating point error (noise on torus)
Date: 10 Mar 2001 04:01:00
Message: <3AA9A753.D4059948@pacbell.net>
Ron Parker wrote:

> I wonder if it has anything to do with the definition of EPSILON.

Naaah... couldn't be that.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/


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From: Wlodzimierz ABX Skiba
Subject: Re: is this bug or floating point error (noise on torus)
Date: 12 Mar 2001 10:34:31
Message: <3aaca637@news.povray.org>
Ron Parker wrote in message ...
> I wonder if it has anything to do with the definition of EPSILON.


Perhaps, but when I replaced camera with typical perspective (with the same
locattion and image sizes) bugs disappeared.

I found at polysolv.c definition of SMALL_ENOUGH with value 1.0e-10 and it is
rather small enough but in torus.c there is value ROOT_TOLERANCE with 1.0e-4 and
I think this is the problem.

Is there any reason why such limitiations can't be changed from script level ?
Perhaps optional float parameter to keyword sturm could help. I haven't windows
compiler (only djgpp or cygwin) but I prefer adventage of build-in editor.

ABX


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From: Vahur Krouverk
Subject: Re: is this bug or floating point error (noise on torus)
Date: 12 Mar 2001 10:47:50
Message: <3AACA979.46C1084F@aetec.ee>
Wlodzimierz ABX Skiba wrote:
> 
> Perhaps optional float parameter to keyword sturm could help. I haven't windows
> compiler (only djgpp or cygwin) but I prefer adventage of build-in editor.
> 
You can use Borland's free command-line compiler to compile GUI version
of POV-Ray. Unfortunately Borland compiler's optimization is
non-existent (at least I am unable to produce faster code with
optimization) and rendering time for test-scene (skyvase.pov) is ca. 50%
slower than MS VC++ or Watcom code.


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From: Wlodzimierz ABX Skiba
Subject: Re: is this bug or floating point error (noise on torus)
Date: 12 Mar 2001 11:24:36
Message: <3aacb1f4@news.povray.org>
Vahur Krouverk wrote in message <3AACA979.46C1084F@aetec.ee>...
> Wlodzimierz ABX Skiba wrote:
> > Perhaps optional float parameter to keyword sturm could help. I haven't
windows
> > compiler (only djgpp or cygwin) but I prefer adventage of build-in editor.
>
> You can use Borland's free command-line compiler to compile GUI version
> of POV-Ray.

I want it since two month but I can't download it.
I have done registration in borland community and got link to download it but
always when I start downloading it is extremly slow and timeouts stops me at 0
bytes.

> Unfortunately Borland compiler's optimization is
> non-existent (at least I am unable to produce faster code with
> optimization) and rendering time for test-scene (skyvase.pov) is ca. 50%
> slower than MS VC++ or Watcom code.

:-(

ABX


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From: Chris Huff
Subject: Re: is this bug or floating point error (noise on torus)
Date: 13 Mar 2001 19:27:53
Message: <chrishuff-C04DF7.14232813032001@news.povray.org>
In article <3aaca637@news.povray.org>, "Wlodzimierz ABX Skiba" 
<abx### [at] abxartpl> wrote:

> Is there any reason why such limitiations can't be changed from script 
> level ?
> Perhaps optional float parameter to keyword sturm could help.

Well, it would require storing another variable, and nobody has ever 
needed to do it before...

-- 
Christopher James Huff
Personal: chrishuff@mac.com, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><


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From: Wlodzimierz ABX Skiba
Subject: Re: is this bug or floating point error (noise on torus)
Date: 14 Mar 2001 16:11:00
Message: <3aaf9814@news.povray.org>
Chris Huff wrote in message ...
> In article <3aaca637@news.povray.org>, "Wlodzimierz ABX Skiba"
> <abx### [at] abxartpl> wrote:
>
> > Is there any reason why such limitiations can't be changed from script
> > level ?
> > Perhaps optional float parameter to keyword sturm could help.
>
> Well, it would require storing another variable

but only in objects with sturm parameter
they are used not so often and even if they are they are only a few

> and nobody has ever needed to do it before...


but perhaps it is worth - not so much to do but more elastic POV ;)

ABX


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