Yeah, but that's basically projecting 3D geometry back onto the sphere (which is also what I ultimately did). There's a faster algorithm that does it "on the sphere", which I thought I used, but turns out I was wrong.

I think it was this one: https://www.math.kent.edu/~zheng/papers/voronoi_paper_update... or this one http://nautilus.fc.ul.pt/jd/jd10sphere.pdf

Ah! I see. Thanks for the reference.