76 lines
1.7 KiB
C
76 lines
1.7 KiB
C
#include "postgres.h"
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#include <math.h>
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#include "utils/geo_decls.h" /* for Pt */
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/* Earth's radius is in statute miles. */
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const double EARTH_RADIUS = 3958.747716;
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const double TWO_PI = 2.0 * M_PI;
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double *geo_distance(Point *pt1, Point *pt2);
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/******************************************************
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*
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* degtorad - convert degrees to radians
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*
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* arg: double, angle in degrees
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*
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* returns: double, same angle in radians
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******************************************************/
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static double
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degtorad(double degrees)
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{
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return (degrees / 360.0) * TWO_PI;
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}
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/******************************************************
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*
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* geo_distance - distance between points
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*
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* args:
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* a pair of points - for each point,
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* x-coordinate is longitude in degrees west of Greenwich
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* y-coordinate is latitude in degrees above equator
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*
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* returns: double
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* distance between the points in miles on earth's surface
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******************************************************/
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double *
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geo_distance(Point *pt1, Point *pt2)
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{
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double long1,
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lat1,
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long2,
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lat2;
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double longdiff;
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double sino;
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double *resultp = palloc(sizeof(double));
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/* convert degrees to radians */
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long1 = degtorad(pt1->x);
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lat1 = degtorad(pt1->y);
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long2 = degtorad(pt2->x);
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lat2 = degtorad(pt2->y);
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/* compute difference in longitudes - want < 180 degrees */
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longdiff = fabs(long1 - long2);
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if (longdiff > M_PI)
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longdiff = TWO_PI - longdiff;
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sino = sqrt(sin(fabs(lat1-lat2)/2.)*sin(fabs(lat1-lat2)/2.) +
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cos(lat1) * cos(lat2) * sin(longdiff/2.)*sin(longdiff/2.));
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if (sino > 1.) sino = 1.;
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*resultp = 2. * EARTH_RADIUS * asin(sino);
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return resultp;
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}
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