A long time ago, when I first started playing with POVRay, it was quite the
trend to have a short POV script for a signature. No one does that anymore it
seems, but I always wanted to try it, so I did! Except the lathe object in the
script appears with artifacts...

I've tried antialiasing, raising the max_trace_level, and adding the sturm
keyword, but none worked. I am using version 3.6.1c.

camera{location y*10 look_at 0}
light_source{<1,30,1>rgb 1}
difference{
  lathe{
    bezier_spline
    4,
    <0,-2>,<2.5,-1.95>,<1,2>,<0,3>
    rotate x*90
    texture{
      pigment{
        bozo scale .25
        color_map{
          [.2 rgb 1.5]
          [1.0 rgbt<1.6,1.5,1.5,.3>]
        }
      }
      finish{
        specular 1
        roughness .0005
        reflection .85
        irid{.25 thickness .25 turbulence 0.5}
      }
    }
  }
  prism{
    linear_sweep
    linear_spline
    0,6,28,
    <-.05,-.33>,<-.38,.66>,<-.71,-.33>,<-.61,-.33>,<-.51,0>,
    <-.25,0>,<-.15,-.33>,<-.05,-.33>,<-.46,.1>,<-.38,.46>,
    <-.31,.1>,<-.46,.1>,<.05,-.33>,<.05,.66>,<.46,.66>,
    <.66,.46>,<.66,.26>,<.46,.06>,<.15,.06>,<.15,-.33>,
    <.05,-.33>,<.15,.56>,<.41,.56>,<.56,.41>,<.56,.31>,
    <0.41,.16>,<.15,.16>,<.15,.56>
    texture{
      pigment{rgb<.6,.4,.1>}
      finish{ambient .15 brilliance 5 metallic specular .8 roughness .01
reflection .65}
    }
  }
}

(Sorry about the lousy formatting...signatures were crammed to make them as
short as possible. I tried to break it up so it is mostly readable :-) )

Thanks in advance!

~Angela Perry

Post a reply to this message

On Thu, 17 Jul 2008 00:30:22 EDT, "Angela" <ang### [at] yahoocom> wrote:

>
>I've tried antialiasing, raising the max_trace_level, and adding the sturm
>keyword, but none worked. I am using version 3.6.1c.

Have you tried the sturm keyword? I've found that if I don't use it I get
artefacts when the object intersects the horizon. 
-- 

Regards
     Stephen

Post a reply to this message

Stephen napsal(a):
> On Thu, 17 Jul 2008 00:30:22 EDT, "Angela" <ang### [at] yahoocom> wrote:
> 
>> I've tried antialiasing, raising the max_trace_level, and adding the sturm
>> keyword, but none worked. I am using version 3.6.1c.
> 
> Have you tried the sturm keyword? I've found that if I don't use it I get
> artefacts when the object intersects the horizon. 

reread the post you quote. You can see she did have tried.

Post a reply to this message

On Thu, 17 Jul 2008 15:26:05 +0200, Jan Dvorak <jan### [at] centrumcz> wrote:

>Stephen napsal(a):
>> On Thu, 17 Jul 2008 00:30:22 EDT, "Angela" <ang### [at] yahoocom> wrote:
>> 
>>> I've tried antialiasing, raising the max_trace_level, and adding the sturm
>>> keyword, but none worked. I am using version 3.6.1c.
>> 
>> Have you tried the sturm keyword? I've found that if I don't use it I get
>> artefacts when the object intersects the horizon. 
>
>reread the post you quote. You can see she did have tried.

I shouldn't do these thinks quickly at work :(
-- 

Regards
     Stephen

Post a reply to this message

That gives me an idea though! Maybe I'll try translating it away from the
origin, just to see if it is the horizon :-) For the location of the artifacts,
that makes sense.

I'm at work too (darn it) so I'll try it when I get home.

~Angela Perry

Stephen <mcavoysAT@aolDOTcom> wrote:
> On Thu, 17 Jul 2008 15:26:05 +0200, Jan Dvorak <jan### [at] centrumcz> wrote:
>
> >Stephen napsal(a):
> >> On Thu, 17 Jul 2008 00:30:22 EDT, "Angela" <ang### [at] yahoocom> wrote:
> >>
> >>> I've tried antialiasing, raising the max_trace_level, and adding the sturm
> >>> keyword, but none worked. I am using version 3.6.1c.
> >>
> >> Have you tried the sturm keyword? I've found that if I don't use it I get
> >> artefacts when the object intersects the horizon.
> >
> >reread the post you quote. You can see she did have tried.
>
> I shouldn't do these thinks quickly at work :(
> --
>
> Regards
>      Stephen

Post a reply to this message

"Angela" <ang### [at] yahoocom> wrote:
> A long time ago, when I first started playing with POVRay, it was quite the
> trend to have a short POV script for a signature. No one does that anymore it
> seems, but I always wanted to try it, so I did! Except the lathe object in the
> script appears with artifacts...
>

Offhand, it looks like the artifacts are from self-shadowing.  After trying the
usual tricks (translating or rotating by a very small amount, etc), I tried
using no_shadow, and the upper ones disappeared.  Unfortunately, this visibly
changes the image without removing some of the lower artifacts.  I am starting
to suspect a bug.

In any case, another work around that reduces (but does not entirely remove) the
artifacts is multiplying the light_source location vector by a higher number.
Code:

light_source{<1,30,1>*100 rgb 1}

With all else the same, the upper, darker artifacts do go away.

     HTH,
  -Reactor

Post a reply to this message

"Angela" <ang### [at] yahoocom> wrote in message 
news:web.487f65ae64250a2e64eed08a0@news.povray.org...
> That gives me an idea though! Maybe I'll try translating it away from the
> origin, just to see if it is the horizon :-) For the location of the 
> artifacts,
> that makes sense.

I've had similar problems in the past when the change of direction between 
two points is too big. Although it may be possible to find a position where 
the artifacts are not very apparent, that's a bit fiddly.

I think you'll find it's a more robust solution to simply add a midpoint, 
reducing the change of direction between each set of points. For example:

camera{location -z*10 look_at 0}
light_source{<1,1,-30> rgb 1}
lathe{
  bezier_spline
  8,
  <0,-2>,<1.5,-1.985>,<1.49,-0.5>,<1.24,0.5>
  <1.24,0.5>,<0.99,1.5>,<0.5,2.5>,<0,3>
  pigment{rgb <1,1,1>}
}

Warning: I've flipped the axes in this example to the default ones which I'm 
more accustomed to and which avoid having to rotate the lathe object.

Regards,
Chris B.

Post a reply to this message

"Chris B" <nom### [at] nomailcom> wrote:
> I think you'll find it's a more robust solution to simply add a midpoint,
> reducing the change of direction between each set of points.

That fixed it Chris, thank you! And thanks everyone else for all the help and
suggestions :-)

~Angela Perry

Post a reply to this message

I ran your eample also version 3.6.1c and don't get any Artifacts.
I used antialise:
+A0.1 +AM2 -J.25 +R3
and tested at two sizes 400*400 and 800*800
No problems anywhere!

Post a reply to this message

On Thu, 17 Jul 2008 22:00:14 EDT, "Angela" <ang### [at] yahoocom> wrote:

>"Chris B" <nom### [at] nomailcom> wrote:
>> I think you'll find it's a more robust solution to simply add a midpoint,
>> reducing the change of direction between each set of points.
>
>That fixed it Chris, thank you! And thanks everyone else for all the help and
>suggestions :-)
>
I'm pleased that you got a solution. I found that when I rotated the lath by 5
degrees the artefacts were not visible.
-- 

Regards
     Stephen

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