Major Description
Across our spatial modules we seem to disagree about the earth's radius when we model it as a sphere.
I think in our haversin implementation we use equitorial (maximum) radius, but maybe in spatial3d we use the earth's mean radius.
I think mean makes more sense: the earth is actually a squashed sphere, so it's polar radius is shorter than its equitorial radius.
I think it's important, when we model the earth as a sphere, that we pick one radius and try to use that one consistently?