POV-Ray : Newsgroups : povray.general : strange coincidental surfaces Server Time
4 Aug 2024 06:15:46 EDT (-0400)
  strange coincidental surfaces (Message 1 to 2 of 2)  
From: Peter Ketting
Subject: strange coincidental surfaces
Date: 30 Jul 2003 03:28:46
Message: <3f2773ae$1@news.povray.org>
This is the strangest effect I have ever encountered so far. I knew there
had to be the usual grainyness that usualy happens with coincidental
surfaces, but I was not expecting this result. Even changing the first union
to difference will not produce the "normal" effect. It would appear it
hollows out the first two cylinders but leaving their surfaces untouched.

Anyone know why it is doing this?


union{
 union {
  cylinder { <-1, 0, 0>, <-1, 0, 1>, 1 }
  cylinder { <1, 0, 0>, <1, 0, 1>, 1 }
  pigment { color rgb <0, 1, 0> }
 }
 union {
  sphere { <-1, 1, 0>, .1 }
  sphere { <1, 1, 0>, .1 }
  sphere { <0, 0, 0>, .1 }
  pigment { color rgb <1, 0, 0> }
 }
 object {
  cylinder { <0, 1, 0>, <0, 1, 1>, 1 }
  pigment { color rgb <0, 0, 1> }
 }
 scale 2
}


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From: Hughes, B 
Subject: Re: strange coincidental surfaces
Date: 30 Jul 2003 05:37:43
Message: <3f2791e7@news.povray.org>
"Peter Ketting" <pet### [at] notmyrealboxcom> wrote in message
news:3f2773ae$1@news.povray.org...
> This is the strangest effect I have ever encountered so far. I knew there
> had to be the usual grainyness that usualy happens with coincidental
> surfaces, but I was not expecting this result. Even changing the first
union
> to difference will not produce the "normal" effect. It would appear it
> hollows out the first two cylinders but leaving their surfaces untouched.
>
> Anyone know why it is doing this?

Yes. Like you said, coincident surfaces. That's all that's happening. It
doesn't always appear as speckles. Shifting the end caps of the blue
cylinder away from the 0 and 1 z planes by 10e-7 was enough to correct it
here. Another tenth factor less and it was the well-known speckled
appearance. Down to 17 decimal places and I got your observed oddity again.

union{
 union {
  cylinder { <-1, 0, 0>, <-1, 0, 1>, 1 }
  cylinder { <1, 0, 0>, <1, 0, 1>, 1 }
  pigment { color rgb <0, 1, 0> }
 }
 union {
  sphere { <-1, 1, 0>, .1 }
  sphere { <1, 1, 0>, .1 }
  sphere { <0, 0, 0>, .1 }
  pigment { color rgb <1, 0, 0> }
 }
 object {
  cylinder { <0, 1, 0-10e-7>, <0, 1, 1-10e-7>, 1 }
  pigment { color rgb <0, 0, 1> }
 }
 scale 2 translate <0,-1,6>
}

light_source {<10,-10,-100>,1}


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