GIS::Distance calculates distances between geographic points on, at the moment,
planet Earth. Various "FORMULAS" are available that provide different levels of
accuracy versus speed.

GIS::Distance::Fast, a separate distribution, ships with C implmentations of
some of the formulas shipped with GIS::Distance. If you're looking for speed
then install it and the ::Fast formulas will be automatically used by this
module.

WWW: https://metacpan.org/release/GIS-Distance