# GIS::Distance::GreatCircle

## NAME

GIS::Distance::GreatCircle - Great circle distance calculations.

## DESCRIPTION

A true Great Circle Distance calculation. This was created because the GIS::Distance::MathTrig formula uses Math::Trig’s "great_circle_distance()" which doesn’t actually appear to use the actual Great Circle Distance formula (more likely Cosine).

A faster ( XS ) version of this formula is available as GIS::Distance::Fast::GreatCircle.

Normally this module is not used directly. Instead GIS::Distance is used which in turn interfaces with the various formula classes.

## FORMULA

c = 2 * asin( sqrt(

( sin(( lat1 - lat2 )/2) )**2 +

cos( lat1 ) * cos( lat2 ) *

( sin(( lon1 - lon2 )/2) )**2

) )

## SUPPORT

See " SUPPORT" in GIS::Distance.

## AUTHORS

See " AUTHORS" in GIS::Distance.

## LICENSE

See " LICENSE" in GIS::Distance.