POV-Ray : Newsgroups : povray.beta-test : isosurface changes Server Time
31 Jul 2024 12:14:37 EDT (-0400)
  isosurface changes (Message 1 to 10 of 10)  
From: Sigmund Kyrre Aas
Subject: isosurface changes
Date: 5 Sep 2001 06:41:19
Message: <d7tbptsuehnfm92j46nja3ofj1lhh5d0vo@4ax.com>
I see that contained_by has changed in such a way that the container
shows up at boundaries. I have a cylindrical object contained by a
box. Squares appear at the ends, whilst in Mega cylindrical ends are
traced. Feature or bug?


------
#declare kurvatur=.4*e;                                
#declare segmentL=.5;                                              
#declare Rad=0; 
isosurface {
    function { kurvatur*sqrt( cos(x/segmentL) )+y^2+z^2-Rad }
    threshold 1
    max_gradient 5.284
    accuracy 0.01
    contained_by{box{-<.79,1,1>,<.79,1,1>}}
    pigment { rgb 1 }
    finish {phong 0.5 phong_size 10}
    scale <1+e,1,1>*.5
   
}

-- 
ICQ 74734588


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From: Jérôme Grimbert
Subject: Re: isosurface changes
Date: 5 Sep 2001 07:08:20
Message: <3B9607A1.14F0545B@atosorigin.com>
Sigmund Kyrre Aas wrote:
> 
> I see that contained_by has changed in such a way that the container
> shows up at boundaries. I have a cylindrical object contained by a
> box. Squares appear at the ends, whilst in Mega cylindrical ends are
> traced. Feature or bug?
>

May I say: RTFM !! (section 6.5.4)


open When the isosurface isn't fully contained within the contained_by object,
there will be a cross section. Where this happens, you will see the surface of
the container. With the open keyword, these cross section surfaces are removed.
The inside of the isosurface becomes visible. Note that open slows down the
render speed. Also, it is not recommended to use it with CSG operations.

But there is nevertheless a bug, because adding 'open' do not work too much
(the cross section is not illuminated, but still cast shadows and block
background.

Updated pov-scene (complete), the Pov-team may want to comment out the 'open'...
---
#declare e=exp(1);
#declare kurvatur=.4*e;
                                
#declare segmentL=.5;                                              
#declare Rad=0; 
isosurface {
    function { kurvatur*sqrt( cos(x/segmentL) )+y^2+z^2-Rad }
    threshold 1
    max_gradient 5.284
    accuracy 0.001 
    open
    contained_by{box{-<.79,1,1>,<.79,1,1>}}
    pigment { rgb 1 }
    finish {phong 0.5 phong_size 10}
    scale <1+e,1,1>*.5
   
}
background { rgb <1,0,0> }
camera { location <3,3,-0> look_at 0 }
light_source { 0,1 translate <6,5,4> }
 light_source { 0,1 translate <6,5,-4> }


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From: Bob H 
Subject: Re: isosurface changes
Date: 5 Sep 2001 07:43:03
Message: <3b960fc7@news.povray.org>

news:3B9607A1.14F0545B@atosorigin.com...
>
> But there is nevertheless a bug, because adding 'open' do not work too
much
> (the cross section is not illuminated, but still cast shadows and block
> background.

If the container box is slightly smaller than 1.0 in that example then it
renders fine.  I have no idea though whether it's a true bug or not, just
that it could be the ever-present coincident surfaces trouble once again.
Sure looks similar since the leftover pieces aren't complete.

Bob H.


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From: Bob H 
Subject: Re: isosurface changes (coincident surfaces known problem)
Date: 5 Sep 2001 07:56:17
Message: <3b9612e1@news.povray.org>
Since this group is possibly going to be visited by new POV-Ray users I
better refer to the documentation (Scene Help) about coincident surfaces.
It's mentioned a few places but the one most likely to read about it is at
3.0 Beginning Tutorial | 3.3 CSG Objects | 3.3.6 CSG Pitfalls.

Bob H.


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From: Sigmund Kyrre Aas
Subject: Re: isosurface changes
Date: 5 Sep 2001 11:36:50
Message: <10hcpt8d5il91g8eetjijhqab2bm8lviuk@4ax.com>

<jer### [at] atosorigincom> wrote:

>May I say: RTFM !!

I did, but it didn't adress my question: _Squares_ appear at the ends,
whilst in Mega cylindrical ends are traced. This has nothing to do
with the open keyword. The iso _is_ fully contained within the box in
the "radial" direction, therefore squares shouldn't appear at the
ends, only a regular circular surface.

sig
-- 
ICQ 74734588


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From: Warp
Subject: Re: isosurface changes
Date: 5 Sep 2001 12:14:49
Message: <3b964f78@news.povray.org>
It would be nice, as noted in the welcome message, if _complete_ (although
minimal) scenes would be included with bug reports. That is, one could
just copy-paste the posted scene to povray and render it and see the
bug.

-- 
#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: Nathan Kopp
Subject: Re: isosurface changes
Date: 5 Sep 2001 17:43:13
Message: <3b969c71@news.povray.org>
"Warp" <war### [at] tagpovrayorg> wrote...
>   It would be nice, as noted in the welcome message, if _complete_
(although
> minimal) scenes would be included with bug reports. That is, one could
> just copy-paste the posted scene to povray and render it and see the
> bug.

I agree!

-Nathan


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From: Nathan Kopp
Subject: Re: isosurface changes
Date: 5 Sep 2001 19:47:52
Message: <3b96b9a8$1@news.povray.org>
"Sigmund Kyrre Aas" <as### [at] studntnuno> wrote...
> I see that contained_by has changed in such a way that the container
> shows up at boundaries. I have a cylindrical object contained by a
> box. Squares appear at the ends, whilst in Mega cylindrical ends are
> traced. Feature or bug?

For the record, there was no bug with POV-Ray in this case.  (See my post to
Sigmund's other post.)  In this case, the user-defined function was trying
to take the square root of a negative number, which is not defined as a real
number.  I don't know why it worked with MegaPOV, because it shouldn't have.

-Nathan


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From: Thorsten Froehlich
Subject: Re: isosurface changes
Date: 5 Sep 2001 20:09:58
Message: <3b96bed6@news.povray.org>
In article <3b96b9a8$1@news.povray.org> , "Nathan Kopp" <nat### [at] koppcom> 
wrote:

> For the record, there was no bug with POV-Ray in this case.  (See my post to
> Sigmund's other post.)  In this case, the user-defined function was trying
> to take the square root of a negative number, which is not defined as a real
> number.  I don't know why it worked with MegaPOV, because it shouldn't have.

It worked with MegaPOV functions because they had funny (and sometime
unpredictable) side effects like taking the absolute value automatically in
some cases...

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org


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From: Mike Williams
Subject: Re: isosurface changes
Date: 5 Sep 2001 20:47:07
Message: <U+8uyKAgasl7Ew85@econym.demon.co.uk>
Wasn't it Nathan Kopp who wrote:
>
>For the record, there was no bug with POV-Ray in this case.  (See my post to
>Sigmund's other post.)  In this case, the user-defined function was trying
>to take the square root of a negative number, which is not defined as a real
>number.  I don't know why it worked with MegaPOV, because it shouldn't have.

I seem to remember that there has been considerable discussion
previously on one of the povray newsgroups about the fact that MegaPOV
isosurfaces incorrectly treat the square roots of negative numbers as if
they were positive numbers.

-- 
Mike Williams
Gentleman of Leisure


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