Gets all points on the path of a spiral around a cylinder. Its `$fa`

, `$fs`

and `$fn`

parameters are consistent with the `cylinder`

module.

## Parameters

`radius`

: The radius of the cylinder. It also accepts a vector`[r1, r2]`

.`r1`

is the bottom radius and`r2`

is the top radius of a cone.`levels`

: The level count is performed every 360 degrees.`level_dist`

: The distance between two vertial points.`vt_dir`

:`"SPI_DOWN"`

for spiraling down.`"SPI_UP"`

for spiraling up. The default value is`"SPI_DOWN"`

.`rt_dir`

:`"CT_CLK"`

for counterclockwise.`"CLK"`

for clockwise. The default value is`"CT_CLK"`

.`$fa`

,`$fs`

,`$fn`

: Check the cylinder module for more details.

## Examples

```
use <helix.scad>;
use <hull_polyline3d.scad>;
$fn = 12;
points = helix(
radius = 40,
levels = 10,
level_dist = 10,
vt_dir = "SPI_UP",
rt_dir = "CLK"
);
for(p = points) {
translate(p) sphere(5);
}
hull_polyline3d(points, 2);
```

```
use <helix.scad>;
use <hull_polyline3d.scad>;
$fn = 12;
points = helix(
radius = [40, 20],
levels = 10,
level_dist = 10,
vt_dir = "SPI_UP",
rt_dir = "CLK"
);
hull_polyline3d(points, 2);
%cylinder(h = 100, r1 = 40, r2 = 20);
```