This thing is awesome. I'm curious about the algorithm used to calculate it. Given a spherical height map, I guess the naive way to solve it would be to basically cast a whole bunch of rays from your starting point and see what you hit, but I wonder if you could do something more clever.

I'm also curious about this note: "Because of refraction, the further away an object is, the higher it will appear." I kind of figured that, like a ship sailing towards the horizon, the distant thing would get shorter as it got further away. I wonder why they get higher instead. Something about big elevation differences?