$KILOMETER_RHO

Number of kilometers around the equator of the earth.

6371.64

$DEG_RATIO

Number of units in a single decimal degree (lat or lon) at the equator.

0.0174532925199433

This value is derived from:

    $gis = GIS::Distance->new( 'Haversine' );
    $DEG_RATIO = $gis->distance( 10,0 => 11,0 )->km() / $KILOMETER_RHO;