POV-Ray : Newsgroups : povray.bugreports : artifacts on lathe object : Re: artifacts on lathe object Server Time
7 Dec 2021 13:34:13 EST (-0500)
  Re: artifacts on lathe object  
From: omniverse
Date: 10 Oct 2017 22:45:00
Message: <web.59dd84e0d40b44f29c5d6c810@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> "David Mandelberg" <dav### [at] mandelbergorg> wrote:
> > When I render the below scene, there are some spurious black artifacts near the
> > center of the red vuvuzela. Without the translation and rotation, the artifacts
> > go away.
>
> I'm not sure how you got them to go away - they certainly don't for me.
>
> I've tried removing the translation and rotation, and moving the camera, the
> light sources, etc.  Gave the finish a little specular reflection - still there.
> I used a cubic_spline instead - still there.
>
> I suppose I ought to mention that when i was deveoping a recent scene with a
> bell - I used a SOR, and I saw the same sort of artefact.

It's when the camera is perpendicular to sides (within vertical extent, ignoring
actual surface curvature) facing camera, so if it gets tilted away enough for
either the base or cap imaginary infinite reach outward to miss the camera it
doesn't show.

I was checking doing that; it can make a line of surface color outward into
space away from the surface, along with the colorless mess. The extent seems to
get confined to the maximum x point, so I don't know if that's a result of
bounding or what but I didn't see it go beyond sides of a box with same
dimensions. Or more precisely, kept within a cylinder of maximum x dimension.

Your bell again below, able to be added directly into lathe scene file and
rendered to show its trouble with this.


#declare bellSpline = array [12] {
     < 3.4688, 0.0001>,
     < 3.4688, 0.0002>,
     < 3.0938, 0.4375>,
     < 2.9375, 0.6250>,
     < 2.4844, 1.3438>,
     < 2.1719, 2.6094>,
     < 2.0469, 4.4688>,
     < 1.9063, 4.6875>,
     < 1.7500, 4.8750>,
     < 1.0313, 5.0938>,
     < 0.0001, 5.1563>,
     < 0.0001, 5.1564>
}

#declare arraySize=11;
#declare Xmax=3.4688;
#declare Ymax=5.1564;

//#declare Bell1 =
union {
 cylinder {<0, 0, 0>, <0, (5.0938/2)+1, 0> 0.125}
 sphere {0, 0.25}
 torus {0.125, 0.125/4 rotate x*90 translate -y*0.25}
// object {Handle translate -y*1}
 sor {
     arraySize+1,
  #for (B, 0, arraySize)
  #local NewSpline = bellSpline [B]/2;
  #declare Xmax = max (Xmax, NewSpline.x);
  #declare Ymax = max (Ymax, NewSpline.y);
  NewSpline,
  #end
     open
 }
 //texture { T_Gold_1B }
// texture { mtex }
 pigment {rgb <1, 1, 0>}
 rotate <-2,0,0>
}


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