Help making a geodesic globe?

Question

I'm planning on making a geodesic globe for a art class. I'm likely going to do a 320 sided version, as the next biggest one is 1280 sides (correct me if i'm wrong on that). But i need to figure out what size to cut the triangles, is there a basic formula to figure it out? If it helps, i'm likely going to go for something basketball sized or the same size as a standard globe, since i'll likely use one as a shell and cover it with the triangles.

Answer 1

A "chord" is a line segment lying on the surface of a circle or sphere. The chord factor of a dome indicates the number of times the "polyhedral face" is being subdivided when it is being projected onto the interior surface of the sphere. In this context, it is symbolized by "ν" (Greek letter nu).

The chord in a dome is calculated as twice the sine of half the "central angle of the chord" (the central angle of the chord is the angle between the center point inside the sphere and the ends of the chord). Determining the central angle usually requires some non-trivial spherical geometry.

In Geodesic Math and How to Use It Hugh Kenner writes, "Tables of chord factors, containing as they do the essential design information for spherical systems, were for many years guarded like military secrets. As late as 1966, some 3v icosa figures from Popular Science Monthly were all anyone outside the circle of Fuller licensees had to go on." (page 57, 1976 edition)

Answer 2

Your dome will approximate a sphere. So calculate an approximate area from the formuli for spheres. Then divide that by 320 sides to get an area per side. Then choose your triangle size accordingly.