> But if you change the second sphere_sweep point from "0" to "1e-3", most of
> the artifacts go away. I also managed to make the artifacts disappear on the
> first half of your example by adding 1e-3 to your second control point. So
> maybe this is some strange precision error that only occurs with certain
> control point positions?

While I was waiting for answers I continued doing the rest of the 
signiature, and I adjusted the z coords of the points that crossed over 
and was amazed to see that some of the holes disappeared.
So then I started sightly shifting thedodgy points on the Z axis. Being 
an orthographic camera you could hardly see the difference but the maths 
obviously could because I mannaged to make it come out fine.

The question is, (and this is the REALLY advanced part) if this is a 
precision problem, what part of the sphere_sweep equation is causing it, 
and is there someway to check the points for artifact causing values 
before you render it?

The final version:

#declare lq=3;

light_source { <30,40,-20> color rgb 1 area_light 
<10,0,0>,<0,10,0>,lq,lq orient circular jitter}
light_source { <-50,40,-20> color rgb 1 area_light 
<10,0,0>,<0,10,0>,lq,lq orient circular jitter}

light_source { <0,0,-30> color rgb 0.2 area_light 
<10,0,0>,<0,10,0>,lq,lq orient circular jitter}

#local ts =2;
#local RS =0.06;
union{
union{
  sphere_sweep {
   b_spline
   20

   <-2,0.8,0>,RS*ts
   <-1,0.8,RS>,RS*ts
   <1,0.8,RS*2>,RS*ts
   <1.4,1,RS>,RS*ts
   <1.2,1.2,RS>,RS*ts
   <1,1,0.00>,RS*ts
   <1,-0.8,RS>,RS*ts
   <1.06,-1.06,RS>,RS*ts
   <1.12,-1,RS*2>,RS*ts
   <1.12,-0.5,RS>,RS*ts
   <1.5,0,0>,RS*ts
   <1.7,-0.5,0>,RS*ts
   <1.7,-1.3,0>,RS*ts
   <2,-0.7,0>,RS*ts
   <2.7,-0.5,0>,RS*ts
   <2.2,0,0>,RS*ts
   <1.7,-0.5,-RS>RS*ts
   <2.2,-1,-RS*2>RS*ts
   <2.7,-1,-RS>RS*ts
   <3.2,-0,0>RS*ts
   tolerance 1.0e-1
  }
  sphere_sweep{
   b_spline
   4
   <0,2,0.12>,RS*ts
   <0,0.9,RS*2>,RS*ts
   <0.2,-1.3,0>,RS*ts
   <-0.2,-2,0>,RS*ts
  }
  translate<-2,0,0>
  scale 1/ts

  translate<-1.6,0.9,0>


  pigment{color rgb <1,0,0>}
  finish{phong 1 reflection <1,0.4,0.4>}
}

union{

  sphere_sweep{
   b_spline
   5
   <-0.5,2,0.12>,RS
   <-0.0,0.9,RS*2>,RS
   <0.2,0,0>,RS
   <0.2,-1.3,0>,RS
   <-0.2,-2,0>,RS
  }

  sphere_sweep{
   b_spline
   6
   <-1,0,0.12>,RS
   <-0.5,1.2,RS*2>,RS
   <1.3,1,0>,RS
   <1.3,0.2,-RS>,RS
   <-0,-0.5,-RS*2>,RS
   <-1,-0.5,-00.3>,RS
  }

  sphere_sweep{
   b_spline
   5
   <1.0,0.7,-RS>,RS
   <1.2,0.3,-RS*2>,RS
   <2.4,0.5,-RS*2>,RS
   <2.5,0.5,0.0>,RS
   <2.5,0.4,RS>,RS
   tolerance 1.0e-1
  }

  sphere_sweep{
   b_spline
   19
   <1.7,-0.7,0>,RS
   <2,-0.7,0>,RS
   <2.7,-0.5,0>,RS
   <2.2,0,0>,RS
   <1.7,-0.5,0.0>RS
   <2,-1,RS>RS
   <2.7,-1,0.0>RS
   <2.95,0.5,0>RS
   <2.9,0.7,-RS>RS
   <2.85,0.5,-RS*2>RS
   <2.9,-1,-RS>RS
   <3.1,-1,-0.00>RS
   <3.4,-0.8,0.00>RS
   <3.9,-0.5,-RS>RS
   <3.4,0,-RS*2>RS
   <3.0,-0.5,-RS>RS
   <3.4,-1,-0.00>RS
   <3.9,-1,-0.00>RS
   <5,-0.5,-0.00>RS
   tolerance 1.0e-1
   translate<-1,0,0>

   //bounded_by{box{<1.2,0.8,0.3><-1.3,-1.2,-0.3>}}
  }

  translate<-1,0,0>

   pigment{color rgb <1,0,0>}
  finish{phong 1 reflection <1,0.4,0.4>}
}
}



-Pete

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