dotSCAD/docs/lib3x-polysections.md

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:

This module can use them to construct the following model:

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:

If your cross section is hollow, set the triangles parameter to "HOLLOW" and index the points as the following:

You can cut triangles by yourself. For example, the above shape can be cut into triangles such as:

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);

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");

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]
    ]
);