POV-Ray : Newsgroups : povray.general : Artifacts with lathe Server Time
4 Aug 2024 18:22:24 EDT (-0400)
  Artifacts with lathe (Message 1 to 8 of 8)  
From: Tyler Eaves
Subject: Artifacts with lathe
Date: 14 Mar 2003 22:00:19
Message: <3e729742@news.povray.org>
I'm getting a weird problem with the lathe object. I'm getting random black 
pixles in a line at a certain point.

Render @ http://cg1.org/lathe.png

Source follows:


camera
{
   location <10,40,-70>
   look_at <0,30,0>
}

light_source
{
   <5,50,-100>,<1,1,.8>
}


sky_sphere
{
   pigment {rgb .5}
}
#declare column = union
{
   
lathe
{
   quadratic_spline
   11
   <4.1,-4>,<4.1,-3>,<4.1,0>,<4,1>,<3.5,1.05>,<3.4,2.5>,<3.2, 
3.2>,<3.2,4.7>,<3.0,5>,<2.8,40>,<2.8,41>
   texture
     {
        pigment
          {
             rgb 1
          }
     }
   sturm

   
}
   torus
     {
        3,.4
        translate y*45
     }
   torus
     {
        3.5,.5
        translate y*55
     }
   
   torus
     {
        3.25,.7
        translate y*50
     }
   
   cone
     {
        <0,45,0>,2.9,<0,55,0>,3.5
     }
   
   
   
   texture
     {
        pigment
          {
             rgb 1
          }
     }
   
}

#declare minx = -40;
#declare maxx = 40;
#declare minz = -40;
#declare maxz = 40;
#declare thespacing = 40;

#declare thex = minx;
#declare thez = minz;

#while (thex <= maxx)
#declare thez = minz;
#while (thez <= maxz)

object
{
   column
   translate <thex,0,thez>
}


#declare thez = thez + thespacing;
#end
#declare thex = thex + thespacing;
#end


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From: Ken
Subject: Re: Artifacts with lathe
Date: 14 Mar 2003 22:29:59
Message: <3E729EFB.40C10F4C@pacbell.net>
Tyler Eaves wrote:
> 
> I'm getting a weird problem with the lathe object. I'm getting random black
> pixles in a line at a certain point.
<snip>
>    sturm

As you are already using the "sturm" keyword there is not much you can
do about it. You are seeing a root solving mathematical error. You might
try moving the control points for your lathe by small amounts or try
using a different spline type for the lathe object to solve the problem.

-- 
Ken Tyler


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From: Tyler Eaves
Subject: Re: Artifacts with lathe
Date: 14 Mar 2003 22:41:10
Message: <3e72a0d6@news.povray.org>
Ken wrote:

> 
> 
> Tyler Eaves wrote:
>> 
>> I'm getting a weird problem with the lathe object. I'm getting random
>> black pixles in a line at a certain point.
> <snip>
>>    sturm
> 
> As you are already using the "sturm" keyword there is not much you can
> do about it. You are seeing a root solving mathematical error. You might
> try moving the control points for your lathe by small amounts or try
> using a different spline type for the lathe object to solve the problem.
> 

Intersting thing is that it seems to occur at the exact height the camera is 
at.


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From: Ken
Subject: Re: Artifacts with lathe
Date: 14 Mar 2003 23:05:37
Message: <3E72A756.1359033@pacbell.net>
Tyler Eaves wrote:

> Intersting thing is that it seems to occur at the exact height the camera is
> at.

Unfortunately it is a problem with both the sor and lathe objects that
has been present since their introduction in POV-Ray v3.0. If there is
a "bugfix" for it, no one has yet to come up with one.

-- 
Ken Tyler


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From: Tyler Eaves
Subject: Re: Artifacts with lathe
Date: 14 Mar 2003 23:47:25
Message: <3e72b05d@news.povray.org>
Ken wrote:

> 
> 
> Tyler Eaves wrote:
> 
>> Intersting thing is that it seems to occur at the exact height the camera
>> is at.
> 
> Unfortunately it is a problem with both the sor and lathe objects that
> has been present since their introduction in POV-Ray v3.0. If there is
> a "bugfix" for it, no one has yet to come up with one.
> 

Drat...

Maybe once I use a more complex texture than pigment{rgb 1} this will be 
alleivated?


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From: Ian J  Burgmyer
Subject: Re: Artifacts with lathe
Date: 15 Mar 2003 00:10:50
Message: <3e72b5da$1@news.povray.org>
Tyler Eaves's furious key-hammering produced this:
>> Unfortunately it is a problem with both the sor and lathe objects that
>> has been present since their introduction in POV-Ray v3.0. If there is
>> a "bugfix" for it, no one has yet to come up with one.
> 
> Maybe once I use a more complex texture than pigment{rgb 1} this will be 
> alleivated?

The problem might not look as obvious but would still exist.  If it is, as Ken
said, a problem with root solving, changing the texture won't fix the problem.

I'd do what Ken suggested -- moving the control points over by a very tiny
amount, small enough not to be noticable but large enough to make a difference
in the calculation (which shouldn't take much).

-- 
/*^*/light_source{100*<-5,2,-5>2}#macro I(i,n)#while(strlen(i)>=n)#local A=asc(
substr(i,n,1));#local a=asc(substr(i,n+1,1));cylinder{<div(A,8)-12,mod(A,8)-4,4
><div(a,8)-12,mod(a,8)-4,4>,0.1pigment{rgb z}}#local n=n+2;#end#end I("ScUe[]"1
/*<*/)I("mkmtlttk"1)//@_$#!,:<"Thhis polysig brought to you by Ian Burgmyer :)"


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From: gonzo
Subject: Re: Artifacts with lathe
Date: 15 Mar 2003 00:54:20
Message: <3e72c00c@news.povray.org>
Tyler Eaves <tyl### [at] cg1org> wrote in message
news:3e729742@news.povray.org...
> I'm getting a weird problem with the lathe object. I'm getting random
black
> pixles in a line at a certain point.
>


quadratic_spline
    12
    <4.1,-4>,<4.1,-3>,<4.1,0>,<4,1>,<3.5,1.05>,<3.4,2.5>,<3.2,
 3.2>,<3.2,4.7>,<3.0,5>,<2.81,30>,<2.79,45>,<2.75,46>

Adding 1 point and moving the last 2 seems to fix it.

RG


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From: William Pokorny
Subject: Re: Artifacts with lathe
Date: 15 Mar 2003 10:50:03
Message: <web.3e734b03b3c2f6dda6ffada60@news.povray.org>
These solver related black pixels are another reason I tend to render images
much larger than the final image size.
Bill P.


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