66 lines
1.5 KiB
C
66 lines
1.5 KiB
C
#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;
|
|
}
|