PostgreSQL Source Code  git master
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. */
17 static const double EARTH_RADIUS = 3958.747716;
18 static 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
30 static 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
49 static 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
96 Datum
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:630
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:2562
#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:64
float8 y
Definition: geo_decls.h:99
float8 x
Definition: geo_decls.h:98