Dan Shriver tabbydan at gmail.com
Wed Jul 17 10:33:26 EDT 2019

```If you're asking me to post my source here it is:

Notes:
1) coshPolygon is corrected to start at 0.0001 not 0 as it was originally
2) If you use coshPolygon2 OpenSCAD helpfully spits out a message saying
not to have points on both sides of the Y axis.  I was suggesting that
maybe instead of the cryptic exception I got a message saying "Do not have
any points X=0" would be nice.  I am seeing that people are saying if you
have two points X = 0 with different Y values that would work, but that
seems like a weird case (as people mention zero thickness)
3) if you make one hypDome things are fine (with coshPolygon starting at
x=0 as it did originally).  However, multiple overlapping, or overlapping
another object causes the cryptic exception

---------------------------------------------

function echoit5(y,x) = echo(y,x) x; //debug

function cosh(x) = (exp(x) + exp(-x))/2;

function coshPolygon(multiplier, power, domain, flip, steps) =
let (flipValue = flip ? cosh( ( multiplier *(pow(domain,power))) ) : 0)
[ for(i = [0.0001: (domain / steps) : domain]) [i, flipValue - cosh(  (
multiplier *(pow(i,power)))  )] ];

function coshPolygon2(multiplier, power, domain, flip, steps) =
[ for(i = [-domain: (2 * domain / steps) : domain]) [i, cosh(  (
multiplier *(pow(i,power)))  )] ];

module hypDome(multiplier = 1, power = 1, domain = 2, flip = true, steps =
10, facets = 20) {
rotate_extrude(\$fn = facets) {
polygon(echoit5("raw polygon",coshPolygon(multiplier, power,
domain, flip, steps)));
}
}

scale([8,8,1]) {
hypDome(1,1,5,true,10, 20);
}

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On Wed, Jul 17, 2019 at 10:00 AM Carsten Arnholm <arnholm at arnholm.org>
wrote:

> On 17.07.2019 15:23, nop head wrote:
> > How does it differ from the OP's?
>
> We might perhaps know if the source is posted.
>
> The claim that touching the Y-axis in a single point is causing
> assertion when used in rotate_extrude can be tested:
>
> rotate_extrude(){
>    polygon([ [0,0],[2,-2], [2,2] ]);
> }
>
> This works fine in OpenSCAD 2019.03.31 and it can be exported
> successfully to various formats, including OFF (sing1.off, vertices=15
> faces=28) and STL (sing1.stl, vertices=84 faces=28).
>
> The assertion occurs in OpenSCAD if you try to union with a cube:
>
> rotate_extrude(){
>    polygon([ [0,0],[2,-2], [2,2] ]);
> }
> cube(1);
>
> Or this way, it also gives an assertion
>
> import("./sing1.stl");
> cube(1);
>
>
> (OFF-version) and union it with a cube as above and save it as test2.off:
>
> shape@ main_shape()
> {
>     polyhedron p("./sing1.off");
>     return p + cube(1);
> }
>
> In this case there is no problem, it works fine as shown in enclosed PNG
> image, and
>
> ===
>
> \$ polyfix test2.off
>
> Parameters:
>    input_file = test2.off
>
>
> polyhedron 0 ================= volume=29.4181, dtol=0.01, atol=1e-06,
> maxiter=10
> iteration 0: vertices=20 faces=38
>               total changes=0
>               no warnings
>
> Summary:
>               polyhedron 0: vertices=20 faces=38 : no warnings
>
> ====
>
>
> Therefore, the problem seen in OpenSCAD is not really in rotate_extrude,
> but how the model is interpreted when subject to union using CGAL. The
> same union using Carve works fine as should be expected.
>
>
> Carsten Arnholm
> _______________________________________________
>
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