Are there any freely available documents for math regarding hex maps? I'm especially searching for hex maps of whole planets. How do such programs as "Traveller Heaven & Earth" calculate the various distances between hexes?
Perhaps there is some material on this topic in classical tabletop/boardgame stuff, but I never played such games and thus have no access to such material yet.
I'm targeting icosahedral maps of planets / worlds in particular.
I'm looking for distance calculations "as the crow flies" regardless of obstacles, as opposed to the length of the most direct valid path.
Any hints on this?