POV-Ray : Newsgroups : povray.advanced-users : Logarithmic spiral tube : Re: Logarithmic spiral tube Server Time
3 Dec 2021 03:05:22 EST (-0500)
  Re: Logarithmic spiral tube  
From: Mike Horvath
Date: 22 Feb 2021 13:53:51
Message: <6033fdbf$1@news.povray.org>
On 1/26/2021 7:42 PM, Robert McGregor wrote:
> Mike Horvath <mik### [at] gmailcom> wrote:
>> How would I create a tube in the shape of a logarithmic spiral? It
>> should have an even thickness. Do I need to use an isosurface once
>> again? Thanks.
> 
> If you have the parametric equation already for a spiral isosurface and you just
> a need a smooth tube, then a difference of two sphere sweeps would render *much*
> faster than an isosurface.
> 
> Just make the radius of the outer one a bit larger and the length of the
> differenced sweep a bit longer, so you get open ends (or just use other
> differencing objects to snip off the ends).
> 
> Maybe something like this non-logarithmic spiral:
> 
> #macro Spherical_Spiral(turns, outer_rad, tube_rad, incr)
>     #local pt_cnt = int(pi/incr+0.5);
>     #local tt = 0;
>     sphere_sweep {
>        cubic_spline
>        pt_cnt
>        #while (tt < pi)
>           #local xt = outer_rad * cos(turns*2*tt) * sin(tt);
>           #local yt = outer_rad * sin(turns*2*tt) * sin(tt);
>           #local zt = outer_rad * cos(tt);
>           <xt, yt, zt> tube_rad
>           #local tt = tt + incr;
>        #end
>        tolerance 0.1
>     }
> #end
> 
> difference {
>     object { Spherical_Spiral(5, 3, 0.12, 0.03) pigment {color Red} }
>     object { Spherical_Spiral(5, 3, 0.10, 0.03) pigment {color Blue} }
>     box {-1, 1 scale 12 translate x*12}
>     rotate y*40
> }
> 
> 
> Cheers,
> Rob
> 
> 

Good idea thank you!

Another option is to create a mesh parametrically.


Mike


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