1 files changed, 104 insertions, 0 deletions
diff --git a/contrib/earthdistance/earthdistance.c b/contrib/earthdistance/earthdistance.c
new file mode 100644
index 0000000..e6ebfd1
--- /dev/null
+++ b/contrib/earthdistance/earthdistance.c
@@ -0,0 +1,104 @@
+/* contrib/earthdistance/earthdistance.c */
+
+#include "postgres.h"
+
+#include <math.h>
+
+#include "utils/geo_decls.h"	/* for Point */
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+PG_MODULE_MAGIC;
+
+/* Earth's radius is in statute miles. */
+static const double EARTH_RADIUS = 3958.747716;
+static const double TWO_PI = 2.0 * M_PI;
+
+
+/******************************************************
+ *
+ * degtorad - convert degrees to radians
+ *
+ * arg: double, angle in degrees
+ *
+ * returns: double, same angle in radians
+ ******************************************************/
+
+static double
+degtorad(double degrees)
+{
+	return (degrees / 360.0) * TWO_PI;
+}
+
+/******************************************************
+ *
+ * geo_distance_internal - distance between points
+ *
+ * args:
+ *	 a pair of points - for each point,
+ *	   x-coordinate is longitude in degrees west of Greenwich
+ *	   y-coordinate is latitude in degrees above equator
+ *
+ * returns: double
+ *	 distance between the points in miles on earth's surface
+ ******************************************************/
+
+static double
+geo_distance_internal(Point *pt1, Point *pt2)
+{
+	double		long1,
+				lat1,
+				long2,
+				lat2;
+	double		longdiff;
+	double		sino;
+
+	/* convert degrees to radians */
+
+	long1 = degtorad(pt1->x);
+	lat1 = degtorad(pt1->y);
+
+	long2 = degtorad(pt2->x);
+	lat2 = degtorad(pt2->y);
+
+	/* compute difference in longitudes - want < 180 degrees */
+	longdiff = fabs(long1 - long2);
+	if (longdiff > M_PI)
+		longdiff = TWO_PI - longdiff;
+
+	sino = sqrt(sin(fabs(lat1 - lat2) / 2.) * sin(fabs(lat1 - lat2) / 2.) +
+				cos(lat1) * cos(lat2) * sin(longdiff / 2.) * sin(longdiff / 2.));
+	if (sino > 1.)
+		sino = 1.;
+
+	return 2. * EARTH_RADIUS * asin(sino);
+}
+
+
+/******************************************************
+ *
+ * geo_distance - distance between points
+ *
+ * args:
+ *	 a pair of points - for each point,
+ *	   x-coordinate is longitude in degrees west of Greenwich
+ *	   y-coordinate is latitude in degrees above equator
+ *
+ * returns: float8
+ *	 distance between the points in miles on earth's surface
+ ******************************************************/
+
+PG_FUNCTION_INFO_V1(geo_distance);
+
+Datum
+geo_distance(PG_FUNCTION_ARGS)
+{
+	Point	   *pt1 = PG_GETARG_POINT_P(0);
+	Point	   *pt2 = PG_GETARG_POINT_P(1);
+	float8		result;
+
+	result = geo_distance_internal(pt1, pt2);
+	PG_RETURN_FLOAT8(result);
+}