With this algorithm you cannot fix the origin
of the helix.
You cannot put them on a lattice for example.



"Grassblade" <nomail@nomail> wrote:
> Mike Williams <nos### [at] econymdemoncouk> wrote:
> > I couldn't find the equation for a helix surface anywhere. Searches just
> > get bogged down with huge numbers of sites that have the equations for a
> > helicoid surface or a helical curve.
> >
> > --
> > Mike Williams
> > Gentleman of Leisure
> Or one could look in one's own site! ;-) I googled for an hour or so but if
> there are any good hits they are hidden very well indeed. Then I stumbled
> on one of your zips that sure enough contained the following:
>
> //Helix
>
> camera { location  <0, 0, -30> look_at <0, 0, 0> angle 10}
>
> sky_sphere { pigment {
>     function{abs(y)}
>     color_map { [0.0 color blue 0.6] [1.0 color rgb 1] }
>   }
> }
>
> light_source {<100,200,-100> colour rgb 1}
> light_source {<-100,-200,-100> colour rgb 0.5}
>
>
> #declare H=0.3;
> #declare R=0.2;
>
> #declare Fx = function(u,v){(1-R*cos(v))*cos(u) }
> #declare Fy = function(u,v){(1-R*cos(v))*sin(u) }
> #declare Fz = function(u,v){ R*(sin(v)) + u*H }
>
> #include "param.inc"
>
>
> object {Parametric(Fx,Fy,Fz,<-10,0>,<10,2*pi>,100,20,"")
>   pigment {uv_mapping checker rgb 0.95 rgb 0.85 scale 0.25}
>   finish {phong 0.5 phong_size 10}
>   rotate y*60
>   no_shadow
> }

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