octsphere-scad

octsphere() is a drop-in replacement for OpenSCAD’s sphere() that builds a geodesic sphere from a subdivided octahedron. Its triangles are spread evenly over the surface instead of bunching at the poles, and its equators are regular polygons lying flat in the XY, YZ and XZ planes, so it lines up with cylinders, prisms and other polygon-based shapes. It can also make a hemisphere with a flat base.

A hemisphere, an octsphere and OpenSCAD's sphere(), all at $fn = 16

Use it

use <octsphere-scad/octsphere.scad>;

octsphere(r = 20);                     // like sphere(r = 20)
octsphere(d = 30);                     // or by diameter
octsphere(r = 20, hemisphere = true);  // upper half, flat base at z = 0

mesh = octsphere(r = 20);              // or get [points, faces]
polyhedron(points = mesh[0], faces = mesh[1]);

With no size it makes a sphere of radius 1, as sphere() does.

Resolution

Resolution works as it does for sphere(): $fn if it’s set, otherwise $fa and $fs. The equator then snaps to the nearest count of the form 4 × 2ⁿ: 4, 8, 16, 32, 64, 128 and so on. At least 4 sides, the bare octahedron. A sphere with an equator of 4 × 2ⁿ sides has 8 × 4ⁿ triangles.

Settings, at r = 20	Equator	Triangles
defaults (`$fa = 12`, `$fs = 2`)	32	512
`$fn = 50`	64	2048
`$fa = 2`, `$fs = 0.5`	128	8192
`$fn = 3` or `4`	4	8

examples/compare.scad draws a hemisphere, an octsphere and OpenSCAD’s sphere() side by side, as in the picture. examples/capsule.scad caps a cylinder with octsphere hemispheres, which meet it edge to edge, beside the same capsule capped with sphere(), whose widest ring falls short of the cylinder’s radius: 9.81 of 10 mm at 16 sides.

Checks

just test takes under a second on OpenSCAD 2026.10.15. It renders seven cases, from the defaults to a fine $fa/$fs, a diameter, a hemisphere and no size at all. It checks each for one closed piece, its size, its triangle count and that every vertex lies on the sphere. just images renders the picture above.

Origin and licence

octsphere() is Amatulic’s Geodesic sphere with 3-axis polygon equators (also on Printables), which builds on Jamie Kawabata’s Geodesic Sphere for OpenSCAD. Both are public domain under CC0. This copy adds the $fa/$fs fallback, so it works without $fn set, plus the example and checks. MIT; see LICENSE.