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#include <math.h>
#include <stdio.h>
#include <string.h>
#include <postgres.h>
#include <utils/geo_decls.h> /* for Pt */
#include <utils/palloc.h> /* for palloc */
/* Earth's radius is in statute miles. */
const EARTH_RADIUS = 3958.747716;
const 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 - 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
******************************************************/
double *
geo_distance (Point *pt1, Point *pt2) {
double long1, lat1, long2, lat2;
double longdiff;
double * resultp = palloc (sizeof(double));
/* 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;
* resultp = EARTH_RADIUS * acos
(sin (lat1) * sin (lat2) + cos (lat1) * cos (lat2) * cos (longdiff));
return resultp;
}
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