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earthdistance.c
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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/* X/Open (XSI) requires <math.h> to provide M_PI, but core POSIX does not */
10#ifndef M_PI
11#define M_PI 3.14159265358979323846
12#endif
13
15
16/* Earth's radius is in statute miles. */
17static const double EARTH_RADIUS = 3958.747716;
18static const double TWO_PI = 2.0 * M_PI;
19
20
21/******************************************************
22 *
23 * degtorad - convert degrees to radians
24 *
25 * arg: double, angle in degrees
26 *
27 * returns: double, same angle in radians
28 ******************************************************/
29
30static double
32{
33 return (degrees / 360.0) * TWO_PI;
34}
35
36/******************************************************
37 *
38 * geo_distance_internal - distance between points
39 *
40 * args:
41 * a pair of points - for each point,
42 * x-coordinate is longitude in degrees west of Greenwich
43 * y-coordinate is latitude in degrees above equator
44 *
45 * returns: double
46 * distance between the points in miles on earth's surface
47 ******************************************************/
48
49static double
51{
52 double long1,
53 lat1,
54 long2,
55 lat2;
56 double longdiff;
57 double sino;
58
59 /* convert degrees to radians */
60
61 long1 = degtorad(pt1->x);
62 lat1 = degtorad(pt1->y);
63
64 long2 = degtorad(pt2->x);
65 lat2 = degtorad(pt2->y);
66
67 /* compute difference in longitudes - want < 180 degrees */
68 longdiff = fabs(long1 - long2);
69 if (longdiff > M_PI)
70 longdiff = TWO_PI - longdiff;
71
72 sino = sqrt(sin(fabs(lat1 - lat2) / 2.) * sin(fabs(lat1 - lat2) / 2.) +
73 cos(lat1) * cos(lat2) * sin(longdiff / 2.) * sin(longdiff / 2.));
74 if (sino > 1.)
75 sino = 1.;
76
77 return 2. * EARTH_RADIUS * asin(sino);
78}
79
80
81/******************************************************
82 *
83 * geo_distance - distance between points
84 *
85 * args:
86 * a pair of points - for each point,
87 * x-coordinate is longitude in degrees west of Greenwich
88 * y-coordinate is latitude in degrees above equator
89 *
90 * returns: float8
91 * distance between the points in miles on earth's surface
92 ******************************************************/
93
95
98{
99 Point *pt1 = PG_GETARG_POINT_P(0);
100 Point *pt2 = PG_GETARG_POINT_P(1);
101 float8 result;
102
103 result = geo_distance_internal(pt1, pt2);
104 PG_RETURN_FLOAT8(result);
105}
double float8
Definition: c.h:587
static double geo_distance_internal(Point *pt1, Point *pt2)
Definition: earthdistance.c:50
static double degtorad(double degrees)
Definition: earthdistance.c:31
static const double EARTH_RADIUS
Definition: earthdistance.c:17
PG_MODULE_MAGIC
Definition: earthdistance.c:14
static const double TWO_PI
Definition: earthdistance.c:18
Datum geo_distance(PG_FUNCTION_ARGS)
Definition: earthdistance.c:97
#define M_PI
Definition: earthdistance.c:11
PG_FUNCTION_INFO_V1(geo_distance)
Datum degrees(PG_FUNCTION_ARGS)
Definition: float.c:2561
#define PG_RETURN_FLOAT8(x)
Definition: fmgr.h:367
#define PG_FUNCTION_ARGS
Definition: fmgr.h:193
#define PG_GETARG_POINT_P(n)
Definition: geo_decls.h:185
uintptr_t Datum
Definition: postgres.h:69
float8 y
Definition: geo_decls.h:99
float8 x
Definition: geo_decls.h:98