Distance calculation from coordinates
This script calculates the distance between two locations, the latitude and
longitude of which are known. The coordinates are given in decimal degrees.
South latitudes and west longitudes are negative.
The calculation formulae is so called great-circle distance calculation, which
assumes a spherical earth. The accuracy of the calculation is not as perfect
as in the more complicated Vincenty's formulae, which assumes the earth to be an
oblate spheroid. The error is however under 0.3% in most cases.