If you think geographically the I<theta> are longitudes: zero at the
Greenwhich meridian, eastward positive, westward negative--and the
-I<phi> are latitudes: zero at North Pole, northward positive,
+I<phi> are latitudes: zero at the North Pole, northward positive,
southward negative. B<NOTE>: this formula thinks in mathematics, not
-geographically: the I<phi> zero is at the Nort Pole, not on the
-west coast of Africa (Bay of Guinea). You need to subtract your
-geographical coordinates from I<pi/2> (also known as 90 degrees).
+geographically: the I<phi> zero is at the North Pole, not at the
+Equator on the west coast of Africa (Bay of Guinea). You need to
+subtract your geographical coordinates from I<pi/2> (also known as 90
+degrees).
$distance = great_circle_distance($lon0, pi/2 - $lat0,
$lon1, pi/2 - $lat1, $rho);