Version: 1.0

Type: Function

Category: Algorithms

License: BSD License

Description: Determines the distance in miles between two latitude/longitude pairs (in degrees) with a slightly modified Haversine formula (from R.W. Sinnott, "Virtues of the Haversine", Sky and Telescope, vol. 68, no. 2, 1984, p. 159). See http://earth.uni-muenster.de/~eicksch/GMT-Help/msg00147.html for more info. It was modified for speed.

# Where:
#  $l1 ==> latitude1
#  $o1 ==> longitude1
#  $l2 ==> latitude2
#  $o2 ==> longitude2
function haversine ($l1, $o1, $l2, $o2)
{
	$l1 = deg2rad ($l1);
	$sinl1 = sin ($l1);
	$l2 = deg2rad ($l2);
	$o1 = deg2rad ($o1);
	$o2 = deg2rad ($o2);
				
	return (7926 - 26 * $sinl1) * asin (min (1, 0.707106781186548 * sqrt ((1 - (sin ($l2) * $sinl1) - cos ($l1) * cos ($l2) * cos ($o2 - $o1)))));
}