1PJ_INIT(3) Library Functions Manual PJ_INIT(3)
2
6 pj_init - initialize cartographic projection
7 pj_init_plus - initialize cartographic projection
8 pj_fwd - forward cartographic projection
9 pj_inv - inverse cartographic projection
10 pj_transform - transform between coordinate systems
11 pj_free - de-initialize projection
12
14 #include <proj_api.h>
15 projPJ pj_init(int argc, char **argv)
17 projPJ pj_init_plus(const char *defn)
19 projUV pj_fwd(projUV val, projPJ proj)
21 projUV pj_inv(projUV val, projPJ proj)
23 int pj_transform(projPJ src_cs, projPJ dst_cs, long point_count,
25 int point_offset, double *x, double *y, double *z)
26 void pj_free(projPJ proj)
28
31 Procedure pj_init selects and initializes a cartographic projection
32 with its argument control parameters. Argc is the number of elements
33 in the array of control strings argv that each contain individual car‐
34 tographic control keyword assignments (+ proj arguments). The list
35 must contain at least the proj=projection and Earth's radius or ellip‐
36 tical parameters. If the initialization of the projection is success‐
37 ful a valid address is returned otherwise a NULL value.
38 The pj_init_plus function operates similarly to pj_init but takes a
40 single string containing the definition, with each parameter prefixed
41 with a plus sign. For example "+proj=utm +zone=11 +ellps=WGS84".
42 Once initialization is performed either forward or inverse projections
44 can be performed with the returned value of pj_init used as the argu‐
45 ment proj. The argument structure projUV values u and v contain re‐
46 spective longitude and latitude or x and y. Latitude and longitude are
47 in radians. If a projection operation fails, both elements of projUV
48 are set to HUGE_VAL (defined in math.h).
49 Note: all projections have a forward mode, but some do not have an in‐
51 verse projection. If the projection does not have an inverse the pro‐
52 jPJ structure element inv will be NULL.
53 The pj_transform function may be used to transform points between the
55 two provided coordinate systems. In addition to converting between
56 cartographic projection coordinates and geographic coordinates, this
57 function also takes care of datum shifts if possible between the source
58 and destination coordinate system. Unlike pj_fwd and pj_inv it is also
59 allowable for the coordinate system definitions (PJ *) to be geographic
60 coordinate systems (defined as +proj=latlong). The x, y and z arrays
61 contain the input values of the points, and are replaced with the out‐
62 put values. The point_offset should indicate the spacing the of x,y,z
63 arrays, normally 1. The function returns zero on success, or the error
64 number (also in pj_errno) on failure.
65 Memory associated with the projection may be freed with pj_free.
67
69 The following program reads latitude and longitude values in decimal
70 degrees, performs Mercator projection with a Clarke 1866 ellipsoid and
71 a 33° latitude of true scale and prints the projected cartesian values
72 in meters:
73 #include <proj_api.h>
74 main(int argc, char **argv) {
76 char *args[] = { "proj=merc", "ellps=clrk66", "lat_ts=33" };
77 projUV p;
78 projPJ pj;
79 if (!(pj = pj_init(3, args)))
81 exit(1);
82 while (scanf("%lf %lf", &p.v, &p.u) == 2) {
83 p.u *= DEG_TO_RAD;
84 p.v *= DEG_TO_RAD;
85 p = pj_fwd(p, pj);
86 printf("%.2f\t%.2f\n", p.u, p.v);
87 }
88 exit(0);
89 }
90
92 libproj.a - library of projections and support procedures
93
95 https://github.com/OSGeo/proj.4/wiki/ProjAPI, proj(1),
96 Cartographic Projection Procedures for the UNIX Environment—A User's
97 Manual, (Evenden, 1990, Open-file report 90-284).
98
100 A list of known bugs can found at https://github.com/OSGeo/PROJ/issues
101 where new bug reports can be submitted too.
102
104 https://proj.org/
105 2020/02/10 Rel. 6.3.1 PJ_INIT(3)