granicus.if.org Git - postgresql/blob - contrib/earthdistance/earthdistance.c

   1 /* contrib/earthdistance/earthdistance.c */
   2
   3 #include "postgres.h"
   4
   5 #include <math.h>
   6
   7 #include "utils/geo_decls.h"    /* for Point */
   8
   9 #ifndef M_PI
  10 #define M_PI 3.14159265358979323846
  11 #endif
  12
  13 PG_MODULE_MAGIC;
  14
  15 /* Earth's radius is in statute miles. */
  16 static const double EARTH_RADIUS = 3958.747716;
  17 static const double TWO_PI = 2.0 * M_PI;
  18
  19
  20 /******************************************************
  21  *
  22  * degtorad - convert degrees to radians
  23  *
  24  * arg: double, angle in degrees
  25  *
  26  * returns: double, same angle in radians
  27  ******************************************************/
  28
  29 static double
  30 degtorad(double degrees)
  31 {
  32         return (degrees / 360.0) * TWO_PI;
  33 }
  34
  35 /******************************************************
  36  *
  37  * geo_distance_internal - distance between points
  38  *
  39  * args:
  40  *       a pair of points - for each point,
  41  *         x-coordinate is longitude in degrees west of Greenwich
  42  *         y-coordinate is latitude in degrees above equator
  43  *
  44  * returns: double
  45  *       distance between the points in miles on earth's surface
  46  ******************************************************/
  47
  48 static double
  49 geo_distance_internal(Point *pt1, Point *pt2)
  50 {
  51         double          long1,
  52                                 lat1,
  53                                 long2,
  54                                 lat2;
  55         double          longdiff;
  56         double          sino;
  57
  58         /* convert degrees to radians */
  59
  60         long1 = degtorad(pt1->x);
  61         lat1 = degtorad(pt1->y);
  62
  63         long2 = degtorad(pt2->x);
  64         lat2 = degtorad(pt2->y);
  65
  66         /* compute difference in longitudes - want < 180 degrees */
  67         longdiff = fabs(long1 - long2);
  68         if (longdiff > M_PI)
  69                 longdiff = TWO_PI - longdiff;
  70
  71         sino = sqrt(sin(fabs(lat1 - lat2) / 2.) * sin(fabs(lat1 - lat2) / 2.) +
  72                         cos(lat1) * cos(lat2) * sin(longdiff / 2.) * sin(longdiff / 2.));
  73         if (sino > 1.)
  74                 sino = 1.;
  75
  76         return 2. * EARTH_RADIUS * asin(sino);
  77 }
  78
  79
  80 /******************************************************
  81  *
  82  * geo_distance - distance between points
  83  *
  84  * args:
  85  *       a pair of points - for each point,
  86  *         x-coordinate is longitude in degrees west of Greenwich
  87  *         y-coordinate is latitude in degrees above equator
  88  *
  89  * returns: float8
  90  *       distance between the points in miles on earth's surface
  91  *
  92  * If float8 is passed-by-value, the oldstyle version-0 calling convention
  93  * is unportable, so we use version-1.  However, if it's passed-by-reference,
  94  * continue to use oldstyle.  This is just because we'd like earthdistance
  95  * to serve as a canary for any unintentional breakage of version-0 functions
  96  * with float8 results.
  97  ******************************************************/
  98
  99 #ifdef USE_FLOAT8_BYVAL
 100
 101 PG_FUNCTION_INFO_V1(geo_distance);
 102
 103 Datum
 104 geo_distance(PG_FUNCTION_ARGS)
 105 {
 106         Point      *pt1 = PG_GETARG_POINT_P(0);
 107         Point      *pt2 = PG_GETARG_POINT_P(1);
 108         float8          result;
 109
 110         result = geo_distance_internal(pt1, pt2);
 111         PG_RETURN_FLOAT8(result);
 112 }
 113 #else                                                   /* !USE_FLOAT8_BYVAL */
 114
 115 double     *geo_distance(Point *pt1, Point *pt2);
 116
 117 double *
 118 geo_distance(Point *pt1, Point *pt2)
 119 {
 120         double     *resultp = palloc(sizeof(double));
 121
 122         *resultp = geo_distance_internal(pt1, pt2);
 123         return resultp;
 124 }
 125
 126 #endif   /* USE_FLOAT8_BYVAL */