Daniel Sullivan wrote:
> 
> Hi there-
> 
> I'm trying to create a 'screen' for my povray bong using tori.
> At the same time I'm trying learn how to use povrays programming
> directives so I do'nt have to write so many lines of code.
> I'm including the code I've already written so you can see what I'm
> attempting to do.
> 
> / Persistence of Vision Ray Tracer Scene Description File
> // File:screen.pov
> // Vers: 3.1
> // Desc: screen created with tori
> // Date: 8/20/98
> // Auth: ArfGrafix
> 
> // ==== Standard POV-Ray Includes ====
> #include "colors.inc"   // Standard Color definitions
> #include "textures.inc" // Standard Texture definitions
> #include "metals.inc"
> 
> // Set a color of the background (sky)
> background { White }
> 
> camera
> {
>   location  <0.0 , 2.0 ,-5.0>
>   look_at   <0.0 , 0.0 , 0.0>
> }
> 
> // create a regular point light source
> light_source
> {
>   0*x // light's position (translated below)
>   color red 1.0  green 1.0  blue 1.0  // light's color
>   translate <-20, 40, -20>
> }
> 
> #declare b_ring =
>   torus { 2, .0625 pigment { P_Brass3 } finish { F_MetalC }  }
> 
>  object { b_ring scale .9 translate .1*y }
>  object { b_ring scale .8 translate .2*y }
>  object { b_ring scale .7 translate .3*y }
>  object { b_ring scale .6 translate .4*y }
>  object { b_ring scale .5 translate .5*y }
>  object { b_ring scale .4 translate .6*y }
>  object { b_ring scale .3 translate .7*y }
>  object { b_ring scale .2 translate .8*y }
>  object { b_ring scale .1 translate .9*y }
> 
> I wrote this piece of code and soon found out that this creates a
> conical series of tori...I tried making a while loop to do this, but was
> flummoxed by the task of having the while do two different operations.
> What I want is series of tori that form a hemisphere rather than a
> cone..that is each torus is a latitudinal strip that trace out a
> hemisphere.
> Thanks in advance for any helpful input that anyone may have.
> 
> Best regards,
> 
> Ron Hicks
> sig### [at] hotmailcom
> http://www.geocities.com/SoHo/1006

First point, do you want the thickness of the ring to decrease as the
height increases? This is what scaling the object is doing. If not then
try

union
{
  #declare a = .1 #while(a < 1)
  torus { cos(asin(a)),.04 translate y*a }
    #declare a = a+.1 #end
  pigment { P_Brass3 }
  finish { F_MetalC }
}

Note I made the minor radius a bit smaller since it's not being scaled.
On a circle drawn on the XY plane, X is proportional to cos(a) and Y is
proportional to sin(a) so you can derive the angle by asin(a), then get
the X (or major radius in this case) by cos(asin(a)).

If you do want the same as you had but a hemispherical version try

#declare a = .1 #while(a < 1)
	object{b_ring scale cos(asin(a)) translate y*a }
	#declare a = a+.1 #end

Hope this helps.
Cheers, PoD.

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