Hi all,

Whats the easiest way of making a spiral which follows the surface of a
cylinder. The only way I can see is to sweep lots of boxes through the
spiral. ie like a sphere_sweep but with a rectangular cross section.

Thanks
jim
-is there an isosurface solution? - although I have a slow computer and the
scene will be rendered with radiosity which may make the render time
unacceptably long :(

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On Thu, 22 Aug 2002 12:50:11 +0100, "James Taylor"
<jim### [at] blueyondercouk> wrote:

>Whats the easiest way of making a spiral which follows the surface of a
>cylinder. The only way I can see is to sweep lots of boxes through the
>spiral. ie like a sphere_sweep but with a rectangular cross section.

A mesh would be the easiest and fastest solution. You can make this
loft either in Rhino (download the demo) or with the Striscia (or
whatever what it was called :) ) macro. Ken should have the links to
both in the links section.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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James Taylor <jim### [at] blueyondercouk> wrote in message
news:3d64d01d@news.povray.org...

> Whats the easiest way of making a spiral which follows the surface of a
> cylinder.

You could code this in a few minutes by placing mesh vertices with loops. It
would be even easier to make a macro which builds the object pointing
straight up in the y direction and then rotating the spiral into the
orientation you desire. Easier yet would be to code the square spiral as a
union of four different meshes. This is inelegant, but would make adding
textures and normals simpler.

Instead of rotating a square to form your spiral, consider rotating a
spline. This would allow for many different and interesting shapes of
spirals. A four point linear spline would also easily produce the square
spiral you mentioned. The uv mapping would be straight forward, so you could
twist your textures as well.

 -Shay

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"Shay" <sah### [at] simcopartscom> wrote in message
news:3d64ea92@news.povray.org...

> Instead of rotating a square to form your spiral, consider rotating a
> spline. This would allow for many different and interesting shapes of
> spirals. A four point linear spline would also easily produce the square
> spiral you mentioned. The uv mapping would be straight forward, so you
could
> twist your textures as well.
>
ahh, it seems so simple now ;)

there's even a spline extrusion macro on oyanale.com if I remember correctly

thanks
jim

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"James Taylor" <jim### [at] blueyondercouk> schrieb im Newsbeitrag
news:3d64d01d@news.povray.org...

> -is there an isosurface solution? - although I have a slow computer and
the
> scene will be rendered with radiosity which may make the render time
> unacceptably long :(
>

I don't know exactly, what you want, but have a look at f_helix1() in
functions.inc. Perhaps f_helix2() will save you the need of an extra
cylinder in the middle. IMO, those functions don't render to slow, but I
might be used to it already.

Marc-Hendrik

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Wasn't it James Taylor who wrote:
>Hi all,
>
>Whats the easiest way of making a spiral which follows the surface of a
>cylinder. The only way I can see is to sweep lots of boxes through the
>spiral. ie like a sphere_sweep but with a rectangular cross section.
>
>Thanks
>jim
>-is there an isosurface solution? - although I have a slow computer and the
>scene will be rendered with radiosity which may make the render time
>unacceptably long :(

Set the "cross section type" parameter of the f_helix1() function to 2
(diamond shape) and then set the cross section rotation angle to 45.
(They're the last two parameters of f_helix1().)

For example:-

#include "functions.inc"

camera { location  <0, 2, -2> look_at 0}

background {rgb 1}

light_source {<-10,20,-10> colour rgb 1}

isosurface {
  function { f_helix1(x,y,z,2,5,0.1,0.3,3,2,45) }
  max_gradient 1.5
  contained_by{box {<-0.4,-2,-0.4> <0.4,1,0.4>}}
  pigment {rgb 1}
}

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