Difference between sweep() and skin()

[jgrizou]

I have been testing the sweep() and skin() function, they are trully amazing. I am still confused about the difference between these two functions. Which is more suited for what? For example, here are two ways to do the same thing:

use <scad-utils/transformations.scad>
use <scad-utils/trajectory_path.scad>
use <scad-utils/trajectory.scad>
use <scad-utils/shapes.scad>

use <skin.scad>
use <sweep.scad>

path_definition = [
trajectory(forward = 10, roll  =  0),
trajectory(forward =  5*3.14159265359, pitch = 180),
trajectory(forward = 10, roll  =  0)
];

// sweep
path = quantize_trajectories(path_definition, steps=100);
sweep(rectangle_profile([2,3]), path);

// skin
trans = [ for (i=[0:len(path)-1]) transform(path[i], rectangle_profile([2,3])) ];

translate([0,10,0])
  skin(trans);

Is there any fundamental differences between these two methods?
Do you recommend one of them for this kind of part?

[NateTG]

I haven't looked at the code in the examples, but it's probably that sweep is for rigidly transformed profiles, and skin is for more plastic changes in profiles.

There's a discussion about the various ways to handle more general notions of extrusion where it came up.

openscad/openscad#114

[kintel]

@jgrizou One primary difference is that skin() will be able to skin differently shaped layers, while sweep can only do linear transformations.

[atartanian]

@jgrizou this is the difference

use <scad-utils/transformations.scad>
use <scad-utils/trajectory_path.scad>
use <scad-utils/trajectory.scad>
use <scad-utils/shapes.scad>

use <list-comprehension-demo/skin.scad>
use <list-comprehension-demo/sweep.scad>

path_definition = [
trajectory(forward = 10, roll  =  0),
trajectory(forward =  5*3.14159265359, pitch = 180),
trajectory(forward = 10, roll  =  0)
];

// sweep
path = quantize_trajectories(path_definition, steps=100);
sweep(rectangle_profile([2,3]), path);

// skin
myLen = len(path)-1;
trans = [ for (i=[0:len(path)-1]) transform(path[i], rounded_rectangle_profile([4,4], i/myLen*2)) ];

translate([0,10,0])
  skin(trans);

[petaflot]

I cannot find rounded_rectangle_profile()... can someone point?

[t-paul]

Probably that one: https://github.com/openscad/scad-utils/blob/26f8c2cf8124cdafe2fc21f9f9bbf2514e404834/shapes.scad#L7

[petaflot]

Probably that one: https://github.com/openscad/scad-utils/blob/26f8c2cf8124cdafe2fc21f9f9bbf2514e404834/shapes.scad#L7

doesn't look rounded to me ; also, see line 16:

// FIXME: Move rectangle and rounded rectangle from extrusion