Paul Bourke posted this in c.g.r.r today:
http://www.swin.edu.au/astronomy/pbourke/modelling/spring/

I fed the parametric function into MegaPov, but I'm not completely happy 
with it. On the page Paul says: "It is a parametric equation in terms of 
parameters u and v. Both range from 0 to 2 pi, increasing u will give 
multiple windings."
When I use <0,2*pi>,<0,2*pi> for the uv boundaries, the scene stays black. 
Can somebody explain me this and what the uv boudary exactly is?

//===scene
#version unofficial MegaPov 0.6;
global_settings {assumed_gamma 1.0}
light_source {<500,500,-500> rgb 1}
camera {location <0,0,-5> look_at <0,0,0>}

#declare r1 = 0.5;
#declare r2 = 0.5;
#declare periodlength=1.5;

parametric {
   function
   r2 * (sin(v) + (periodlength * u / pi)),
   (1 - (r1 * cos(v))) * cos(u),
   (1 - (r1 * cos(v))) * sin(u)
   
   <-2*pi,-2*pi>,<2*pi,2*pi> //<0,2*pi>,<0,2*pi>
   <-2,-1.5,-1.5>,<2,1.5,1.5>
   accuracy 0.01
   precompute 20,[x,y,z]
   pigment {rgb 1}
}
//===end scene


Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

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In article <8FE### [at] povrayorg>, ing### [at] homenl (ingo) wrote:

> When I use <0,2*pi>,<0,2*pi> for the uv boundaries, the scene stays 
> black. 

This is the same as saying:
u = from 0 to 0
v = from 2*pi to 2*pi

I think you want to use <0, 0>, < 2*pi, 2*pi>.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Chris Huff wrote:

>This is the same as saying:
>u = from 0 to 0
>v = from 2*pi to 2*pi
>

Ah, this makes sense and I can' read :(

Is precompute limited to 20? At 21 it POV says "Precompute: invalid depth" 
.

Thanks Chris,
Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

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In article <8FE### [at] povrayorg>, ing### [at] homenl (ingo) wrote:

> Is precompute limited to 20? At 21 it POV says "Precompute: invalid 
> depth" 

It can not be less than 1 or more than 20. Why? I have no idea...I don't 
even really know what it does.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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