I have some sql to define some functions for doing conversions between
cube and latitude and longitude (as float8) and for calculating
great circle distances between cubes (using a spherical model of the earth).
I am not sure the code is suitable for contrib.
The code picks a radius of the earth in meters. Other people may choose to
use different units or even use a different radius in meters.
I have grants in the code to make the cube functions and the functions
defined by the script as execute for public. (The cube stuff needs to be
done as postgres since a type is created, but then the functions aren't
generally accessible by default.)
The script is about 5K.
Some people might find this useful as there are some advantages to keeping
track of locations on the earth using cube (with 3D coordinates) as opposed
to using point (with 2D coordinates).