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#include "postgres.h"
#include <math.h>
#include "utils/geo_decls.h" /* for Pt */
/* Earth's radius is in statute miles. */
const double EARTH_RADIUS = 3958.747716;
const double TWO_PI = 2.0 * M_PI;
double *geo_distance(Point *pt1, Point *pt2);
/******************************************************
*
* 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 sino;
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;
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.;
*resultp = 2. * EARTH_RADIUS * asin(sino);
return resultp;
}
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