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# polysections
Crosscutting a tube-like shape at different points gets several cross-sections. This module can operate reversely. It uses cross-sections to construct a tube-like shape. For example, imagine that you have the following cross-sections:
![polysections](images/lib3x-polysections-1.JPG)
This module can use them to construct the following model:
![polysections](images/lib3x-polysections-2.JPG)
Looks like extruding along the path? Yes, it can perform the task; however, it's more flexible.
You can also view it as a better polyline3d module if you want. If you have only the points of a path, using `polyline3d` or `hull_polyline3d` is a simple solution. If you know the cross sections along a path, you can use `polysections` to do more.
When using this module, you should use points to represent each cross section. The points of your cross section should have count-clockwise indexes. For example:
![polysections](images/lib3x-polysections-10.JPG)
If your cross section is hollow, set the `triangles` parameter to `"HOLLOW"` and index the points as the following:
![polysections](images/lib3x-polysections-5.JPG)
You can cut triangles by yourself. For example, the above shape can be cut into triangles such as:
![polysections](images/lib3x-polysections-6.JPG)
The indexes of the above triangles is:
[
[0, 3, 1],
[1, 3, 4],
[1, 4, 2],
[2, 4, 5],
[2, 5, 0],
[0, 5, 3]
]
When defining triangles, you can use clockwise or counter-clockwise indexes.
## Parameters
- `sections` : A list of cross-sections. Each cross-section is represented by a list of points. See the example below.
- `triangles` : `"SOLID"` (default), `"HOLLOW"`, or user-defined indexes. See example below.
## Examples
use <rotate_p.scad>;
use <polysections.scad>;
section1 = [
[20, 0, 0],
[18, 9, 0],
[15, 10, 0],
[10, 0, 0]
];
// spin section1
sections = [
for(i = [0:55])
[
for(p = section1)
let(pt = rotate_p(p, [90, 0, 10 * i]))
[pt[0], pt[1] , pt[2] + i]
]
];
polysections(sections);
![polysections](images/lib3x-polysections-7.JPG)
use <rotate_p.scad>;
use <polysections.scad>;
section1 = [
// outer
[20, 0, 0],
[18, 9, 0],
[15, 10, 0],
[10, 0, 0],
// inner
[18, 2, 0],
[17, 7, 0],
[15, 7, 0],
[12, 2, 0]
];
// spin section1
sections = [
for(i = [0:55])
[
for(p = section1)
let(pt = rotate_p(p, [90, 0, 10 * i]))
[pt[0], pt[1] , pt[2] + i]
]
];
polysections(sections, "HOLLOW");
![polysections](images/lib3x-polysections-8.JPG)
use <rotate_p.scad>;
use <polysections.scad>;
section1 = [
// outer
[30, 0, 0],
[15, 10, 0],
[10, 0, 0],
// inner
[26, 1, 0],
[15, 8, 0],
[12, 1, 0],
];
// spin section1
sections = [
for(i = [0:55])
[
for(p = section1)
let(pt = rotate_p(p, [90, 0, 10 * i]))
[pt[0], pt[1] , pt[2] + i]
]
];
polysections(
sections = sections,
triangles = [
[0, 3, 1],
[1, 3, 4],
[1, 4, 2],
[2, 4, 5],
[2, 5, 0],
[0, 5, 3]
]
);
![polysections](images/lib3x-polysections-9.JPG)