PoD wrote:
> 
> 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.

Pod-

many thanks for your help with the routine.....after a little fiddling
with what you had suggested I came up with a with a real nice screen for
my povray bong.
after I had posted the query to the newsgroup I felt adventurous and
tried to formulate my own routine for creating the hemisphere after
scratching the problem out with pencil and paper and here's what I came
up with...but with strange results.

You can find my improved povray bong in the povray immages group:)

==== Standard POV-Ray Includes ====
#include "colors.inc"	// Standard Color definitions
#include "textures.inc"
#include "metals.inc"

camera
{
  location  <0.0 , 2 ,-5>
  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>
}


// Set a color of the background (sky)
background { White }

   
  


   

#declare m =2;  
   #declare c = 0;
        #while (c < 90)
        #declare m = m*cos(c) 
            torus { m, m/16 translate sin(c)*y pigment { Red } }
         #declare c = c+10;
        #end
    

What am I missing here?

Many thanks in advance.

Best Regards,

Ron Hicks
http://www.geocities.com/SoHo/1006
sig### [at] hotmailcom

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