[sterlind]

I did try the code snippet technique, but unfortunately it got it wrong. For example, I gave it code that drew arcs but didn't follow the shortest great-circle distance, and it gave me several plausible-looking approaches that were completely wrong (e.g. telling ctx.arc to draw counterclockwise, which does the wrong thing because it needs to use projections instead.)

I eventually just asked it to compute coordinates to a point c perpendicular to the midpoint on the great arc between a and b, such that the angle between ab and ac is alpha. I tried for hours, asking it to work out equations and name the mathematical identities it used etc. but it was all gibberish.