In article <3adbb604$1@news.povray.org> , "David C. Jones" 
<dav### [at] nightswimmingcom> wrote:

The group povray.programming is for discussing the source code of
POV-Ray, not the scene description language. There is an article in
p.announce.f-a-q group entitled, "Welcome To the POV-Ray News Groups".
This article explains where to post questions in the most relevant
groups. Follow-ups to povray.newusers please.

> So, I spent all day today trying to build a cartoon head for a personal
> project and I got to where I had to do the mouth.  One idea was to use a
> difference command and whack out cavity for the mouth and I ended up with a
> rather odd render.  Right in the center of the render is black dot that
> seemingly comes from nowhere.  Two odd things of note:
>
> 1) If I union the sphere instead of difference it, the black dot goes away
> 2) If I change the camera location or rotate the object, the black dot
> appears on the same location in the render (as opposed to moving in
> conjuction with the camera or the rotation).
>
> Both of these lead me to believe that the artifact is a rendering error and
> not a free object.  To see the pictures, go to
> http://www.nightswimming.com/davy/pov.  The code is listed below and the
> relevant difference/union command is the very last one at the end of the
> file, but I wouldn't actually render it unless you have a lot of patience.
> Rendering the union takes 11 seconds but rendering the difference takes 15
> minutes (both on a PIII-700 machine).  I've decided to take a different
> approach on the mouth, but I was wondering if anybody knew about this.
>
> Davy
>
> #macro SphToRec (rho, theta, phi) rho*<sin(phi)*cos(theta),
> sin(phi)*sin(theta), cos(phi)> #end
> #macro PlrToRec (rho, theta, zed) <rho*cos(theta),zed,rho*sin(theta)> #end
>
> #include "colors.inc"
>
> background{ SkyBlue }
>
> #declare Cam_Rot = -90;
>
> camera {
>   location <5 10, -13>
>   look_at <0, 10, 10>
> }
>
> light_source { <1000, 1000, -1000> 0.4*<1,1,1> }
> light_source { <-1000, 1000, -1000> 0.4*<1,1,1> }
> light_source { <0, .1, -1000> 0.9*<1,1,1> }
>
>
>
> plane {
>   y, 0
>   texture {
>     pigment {
>       checker
>         color Blue
>         color Green*1.03
>   } scale <5,1,5>
>  }
> }
>
> #declare HeadNoMouth = object {
> union { // head without mouth
>
>   blob
>
>
>     threshold .1
>
>     sphere { // head
>       <0, 10, 0> 5 .9
>       texture { pigment { Flesh } }
>     }
>
>     sphere { // mouth-jaw
>       <0, 0, 0> 1 .9
>       scale <6.25,3.5,5>
>       translate <0,8.1,0>
>       texture { pigment { Flesh } }
>     }
>
>     sphere { // right eye
>       <0,0,0> 1 .9
>       scale <.85,1.25,.33>
>       rotate <7.5,0,0>
>       translate <.45,11,-4>
>       texture { pigment { White*1.25 }}
>     }
>
>     sphere { // left eye
>       <0,0,0> 1 .9
>       scale <.85,1.25,.33>
>       rotate <7.5,0,0>
>       translate <-.45,11,-4>
>       texture { pigment { White*1.25 }}
>     }
>
>     sphere { // right pupil
>       <0,0,0> .25 .9
>       translate <.45,10.25,-4.25>
>       texture { pigment { Black }}
>     }
>
>     sphere { // left pupil
>       <0,0,0> .25 .9
>       translate <-.45,10.25,-4.25>
>       texture { pigment { Black*1.5 }}
>     }
>
>     sphere { // nose
>       <0,9,-4> .5 .9
>       scale <1,1,1.05>
>       texture { pigment { Flesh } }
>     }
>
>   } // head pieces
>
>   sphere { // yellow hair
>     <0,10.,.99> 4.8
>     texture {
>       pigment { Yellow transmit .65}
>     }
>   } // yellow hair
>
>   #declare hairphi=0;
>   #while (hairphi<pi/1.25)
>     #declare hairtheta=2*pi;
>     #while (hairtheta>0)
>         cone {
>           SphToRec(4  ,hairtheta,hairphi-
> (pi/100)*sin(5*abs(hairphi-pi)*abs(hairtheta-pi))) , .33
>           SphToRec(4.87,hairtheta,hairphi-
> (pi/100)*sin(5*abs(hairphi-pi)*abs(hairtheta-pi))) , .05
>           texture { pigment { Yellow/10 }}
>           rotate <0,0,-90>
>           translate <0,10,1>
>         }
>       #declare hairtheta=hairtheta-pi/25 +
> (pi/75)*cos(abs(hairphi-pi)*abs(hairtheta-pi));
>     #end
>     #declare hairphi=hairphi+pi/45 ;
>   #end
>
>   object { // left ear
>     union
>
>       difference {
>         sphere { <0,0,0> 1 }
>         sphere { <0,0,0> .6 }
>         box {
>           <2,2,0>
>           <-2,-2,-2>}
>       } // difference
>     torus { 0.8 0.2 rotate <90,0,0>}
>     } // union
>     texture { pigment { Flesh } }
>
>     scale <.9,1.25,.75>
>     translate <5.,10,-1>
>
>   } // left ear
>
>   object { // right ear
>     union
>
>       difference {
>         sphere { <0,0,0> 1 }
>         sphere { <0,0,0> .6 }
>         box {
>           <2,2,0>
>           <-2,-2,-2>}
>       } // difference
>     torus { 0.8 0.2 rotate <90,0,0>}
>     } // union
>     texture { pigment { Flesh } }
>
>     scale <.9,1.25,.75>
>     translate <-5,10,-1>
>
>   } // object right ear
>
> } // head without mouth
>
> } //  HeadNoMouth
>
> // If this union is changed to a difference, the artifact appears.  The fact
> that HeadNoMouth
> // is made a separate object is irrelevant.  I built the same object without
> the declare and the artifact still appears.
>
> union
>
>   object { HeadNoMouth }
>   sphere {
>     <0,0,0> 1
>     scale <3/4,1/3,1/2>
>     rotate <0,-25,0>
>     translate <2,8,-3.5>
>     texture { pigment { Red } }
>   }
>    // rotate <0,25,0>
> } // difference



____________________________________________________
Thorsten Froehlich
e-mail: mac### [at] povrayorg

I am a member of the POV-Ray Team.
Visit POV-Ray on the web: http://mac.povray.org

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