Vincenty calculates the geographical distance (in kilometers or miles) between 2
points with extreme accuracy.

This library implements Vincenty's solution to the inverse geodetic problem. It
is based on the WGS 84 reference ellipsoid and is accurate to within 1 mm (!) or
better.

This formula is widely used in geographic information systems (GIS) and is much
more accurate than methods for computing the great-circle distance (which assume
a spherical Earth).