That is just a regular polyhedron, with 8 points.
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#polygon

You just need the list of xy points. This is a 2D shape, so remember to
extrude it.

Msquare

On Fri, 2 Jul 2021 at 16:26, disruptivesolutionsnl@gmail.com wrote:

You can make an arbitrary 8 sided shape by giving a list of vertices to
polygon(). If you want to specify the angles you would need to use some
trigonometry to work out the vertex positions, or perhaps use a library
with turtle mode paths.

On Fri, 2 Jul 2021 at 15:26, disruptivesolutionsnl@gmail.com wrote:

On Fri, 2 Jul 2021 16:26:09 +0200, you wrote:

On Fri, 2 Jul 2021 16:26:09 +0200, you wrote:

Hi Ben,

I'm newish here too, and an OS novice, but one of the books I've bought
has some examples from which I've extracted the following. Although it's
not a close match, with a revised function it might be a start.

function cartesian(radius,angle)=
[radiuscos(angle),radiussin(angle)];

module triangle(p1,p2,p3) {
polygon([p1,p2,p3]);
}

module regular_polygon(poly_edges,poly_radius) {
for(n=[0:poly_edges-1]) {
p1 = cartesian(poly_radius,n*360/poly_edges);
p2 = cartesian(poly_radius,(n+1)*360/poly_edges);
triangle([0,0],p1,p2);
}
}

// Octagon example
poly_edges = 8;
poly_radius = 20;
poly_height = 3;
linear_extrude(poly_height)
regular_polygon(poly_edges,poly_radius);

It's not super-obvious, but OpenSCAD has a built-in way to do this:

circle(r=poly_radius, $fn=poly_edges);

Additional regular polygon tips:

Note that OpenSCAD measures the "radius" of the polygon from the center
to the vertices.

function adjustr(r, n) = r / cos(360/n/2);

will give you an "adjusted" radius, such that circle(r=adjustr(r, n),
$fn=n) will give you a polygon where "r" is the distance from the center
to the middle of the edges.

Also note that OpenSCAD circle() behavior puts one vertex at [r, 0], so
that a square ends up diamond-oriented.  That's not wrong, but sometimes
it's more convenient to have an edge there.  For that, you want

rotate(360/n/2) circle(...);

If you combine those:

rotate(360/n/2) circle(r=adjustr(r, n), $fn=n);

then you end up with a polygon where one edge is aligned with the Y axis
and has its center at [r, 0].  If the number of sides is even, another
Y-aligned edge is at [-r,0], and if it's divisible by four then there
will be X-aligned edges at [0,r] and [0,-r].

On 7/2/2021 1:10 PM, Jordan Brown wrote:

Perhaps circle (and cylinder and sphere) should get additional options
so that these adjustments are built in, rather than everybody needing to
layer adjustments on top.

For the radius adjustment, there could be "ir", "or", "id", and "od"
parameters. "or" and "od" would be aliases for the current "r" and "d"
and specify to-vertex dimensions, while "ir" and "id" would specify
to-edge dimensions.

I don't know about the rotation adjustment, but perhaps it would be a
boolean or perhaps it would be an "align" parameter with options
"vertex" and "edge".

It's hard to tell when adding these small tweaks to the base (thus
cluttering the base more) is a win over having people or libraries
invent new names for new operations that are almost the same as the
existing operations.

It’s because you use Gmail.
Gmail has a policy that it will never show you an email that it can tell was sent by yourself.
Makes me crazy when testing groups.
I guess they think it would insult your memory?

--
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dbg@SCIzzL.com

On Fri, Jul 2, 2021, at 12:36 PM, Terry wrote:

Something like this?

r=50; sides=8; small_ang=30;
poly = [
for (a=[0:90:359],b=[-0.5,0.5])
let(ang=a+bsmall_ang)
r[cos(ang), sin(ang)]
]
polygon(poly);

Or do you need specific interior angles on the polygon?

• Revar

Terry,

Firstly we do not use OS as an abbreviation for OpenSCAD it gets confused for Operating System,
which is a more common term. What version of the OS are you running?

So what books??

BTW, people have missed the subtlety of the original request; different angles/lengths.

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