Le_Forgeron <jgr### [at] freefr> wrote:
> Le 22/07/2011 10:27, 43oasis nous fit lire :
> > Hello
> >
> > I use this code to produce the body of a rocket :
> >
> > #declare forme = sor { 16,
> >                        <0.0005,-6>,
> >                        <1.0,-4>,
> >                        <1.01,-2>,
> >                        <1.15,0>,
> >                        <1.35,2>,
> >                        <1.55,4>,
> >                        <1.69,6>,
> >                        <1.8,8>,
> >                        <1.89,10>,
> >                        <1.925,12>,
> >                        <1.79,14>,
> >                        <1.5,16>,
> >                        <0.99,18>,
> >                        <0.175,20>,
> >                        <0.07,20.1>
> >                        <0.0005,23>
> >                        hollow
> >                      }
> > later restricted to the sections of interest by various "difference" with
> > co-axial cylinders in CSG operations, but this makes no ... difference.
> >
> > When textured with :
> >
> > #declare txtr = texture { pigment { color Red }
> >                          finish { ambient 0.05 diffuse 0.8 }
> >                         }
> >
> > I get strange results, with the object beeing usually OK, but, for some
> > orientations and distances to the observer, full of "semi-random" holes
> > (perpendicular to the axis of the SOR), shape errors, and granite-like black
> > imperfections.
> >
> > Which parameter is wrong ?
> > I set :
> > global_settings { max_trace_level 256 assumed_gamma 1.0 }
>
> Sor documentation:
> >
http://wiki.povray.org/content/Documentation:Reference_Section_4.1#Surface_of_Revolution
>
> have you tried to add "sturm" before "hollow" ?
>
> what and where is your camera ? your light sources ?

Ah, interesting : by adding the "sturm" specification (more precise maths), I
remove almost all the black defects, leaving mainly the shape errors.
I removed the "hollow", which I do not use in fact ; no difference.

Here is the camera and lightsource specs :

.....
#declare Position = (1-klok)*100*<100,15,80> - 10*<120,7,50>;
// Part of an animation, 0<=klok<=2 ; the effect occur around klok = 1.06.
// That is Position = <-1776.4413,-156.4662,-961.1530>
// This is where the SOR is translated in my scene
.....
camera {

    #declare xS = 0;
    #declare yS = 1;
    #declare zS = 0;
    up <xS,yS,zS>
    right x*image_width/image_height

    angle 1
    location <0,0,-2000>
    look_at (Position - 9*x)
}
.....
light_source {                    // far enough to avoid problems ...
  0
  color White
  translate <20000, 30000, -10000>
}

For zCam <= -1958.5 or zCam >= 2003.5, all the defects in my scene (where there
are other SORs, affected by the same problem) are gone.

Gilles

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