MMKDistance

extern double MMKDistance(MMKPoint *firstPoint, MMKPoint *secondPoint)

Calculate the great-circle distance between two points on a sphere with a radius equal to the Earth's radius using the haversine formula described here: http://en.wikipedia.org/wiki/Haversine_formula

This formula is numerically better-conditioned for small distances, according to http://en.wikipedia.org/wiki/Great-circle_distance