Wasn't it Tim McMurdo who wrote:
>I am writing an include file to generate the shrouds for the USS Niagara
>model I am working on.
>
>My problem is in the ratlines (those horizontal ropes that hang between the
>vertical shrouds).  I  want the rat lines to hang so that the lowest point
>is 150mm below the ponit at which they join the shroudes. My first idea was
>to keep it simple. I scaled a half torus so that is fit between the shrouds.
>The problem is obvious, as the torus stretches the smaller diameter of the
>torus also stretches, resulting in a varying diameter in the ratline.
>
>I then thought that I would try to write a #while loop that would place
>spheres along the curve of a catenary. However, my math skills are not up to
>the task.
>
>Here is my call for help....
>
>Can anybody help me with a formula for either a catenary of even a parabola
>whose curve has a vertex of  <0,-150,0> and has X intercepts of <X,0,0> with
>X being a variable?
>
>And while I am asking.....does anybody have a nice rope texture that I could
>put on the finished shrouds?
>
>Thanks,
>
>Tim


You might consider using Chris Colefax's "link.inc" file to do the hard
work. Something like this, perhaps:-

#declare MyRope = union {
  sphere {<0, 0, 0.5>, 1}
  sphere {<0, 0, -0.5>, 1}
  pigment {rgb <.8,.6,.4>}
  scale <1.8, 1, 1>
}

#declare link_object = MyRope                                
#declare link_count = 70;            
#declare link_looseness = 2;
#declare link_twist = 40;
#declare link_twist_turb = 0.1; 
#declare camera_sky = <0,1,0.1>;
#declare link_point1 = <5, 4, -4>;
#declare link_point2 = <-5, 4, -4>;
   
#include "link.inc"

-- 
Mike Williams
Gentleman of Leisure

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