

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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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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