POV-Ray : Newsgroups : povray.text.tutorials : spiral Server Time
28 Sep 2021 16:03:03 EDT (-0400)
  spiral (Message 11 to 12 of 12)  
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From: zeroin23
Subject: Re: spiral
Date: 20 Jul 2007 02:30:02
Message: <web.46a05599cef26043f16edaaa0@news.povray.org>
Hay is this a helix?

The parametric v controls the width of ribbon while u controls the number of
turn. I am checking as for some camera location, it looks like a helix, but
location <-10, 10, -30> it looked really weird.

I am using this for my alpha protein structure.
Any clues for rendering beta sheets?

thx

======================
 #include "colors.inc"
  background{White}
  camera {
    angle 20
    location <10, 10, -30>
    look_at <0, 1, 0>
  }
  light_source { <20, 20, -20> color White }
  parametric {
    function {sin(u)+v}
    function {cos(u)+v}
    function {u}

    <pi,0>, <8*pi,0.6>
    //contained_by { sphere{0, 10} }
    contained_by{box{-20,20}}
    max_gradient 0.1
    accuracy 0.0001
    precompute 10 x,y,z
    pigment {rgb <1,0,0>}
  }


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From: Mike Williams
Subject: Re: spiral
Date: 20 Jul 2007 03:20:40
Message: <EByy$FAUEGoGFwDe@econym.demon.co.uk>
Wasn't it zeroin23 who wrote:
>Hay is this a helix?

The path of a thin strip of that is a helix, e.g. if you set the limits
to  <pi,0> <8*pi,0.01>  then you get a thin line that follows a helical
path.

The problem is that the width of the ribbon consists of points that are
always in the positive x and y directions, which isn't like anything
you'd expect.

This gives a ribbon that has a surface parallel to the axis. The
ribbon's width is in the z direction.
    function {sin(u)}
    function {cos(u)}
    function {u+v}

This gives a ribbon that has a surface that is perpendicular to the
axis. The ribbon's width is outwards from the centre in the direction
<sin(u),cos(v)>
    function {sin(u)*(1+v)}
    function {cos(u)*(1+v)}
    function {u}

-- 
Mike Williams
Gentleman of Leisure


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