1PJ_INIT(3U)                                 PJ_INIT(3U)
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NAME

6       pj_init - initialize cartographic projection
7       pj_init_plus  -  initialize cartographic projec‐
8       tion
9       pj_fwd - forward cartographic projection
10       pj_inv - inverse cartographic projection
11       pj_transform - transform between coordinate sys‐
12       tems
13       pj_free - de-initialize projection
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SYNOPSIS

16       #include <proj_api.h>
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18       projPJ pj_init(int argc, char **argv)
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20       projPJ pj_init_plus(const char *defn)
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22       projUV pj_fwd(projUV val, projPJ proj)
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24       projUV pj_inv(projUV val, projPJ proj)
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26       int pj_transform(projPJ src_cs, projPJ dst_cs, long point_count,
27                        int point_offset, double *x, double *y, double *z)
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29       void pj_free(projPJ proj)
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DESCRIPTION

33       Procedure pj_init selects and initializes a car‐
34       tographic projection with its  argument  control
35       parameters.   Argc  is the number of elements in
36       the array of control strings argv that each con‐
37       tain individual cartographic control keyword as‐
38       signments (+ proj  arguments).   The  list  must
39       contain at least the proj=projection and Earth's
40       radius or elliptical parameters.   If  the  ini‐
41       tialization  of  the  projection is successful a
42       valid address is returned otherwise a NULL  val‐
43       ue.
44
45       The  pj_init_plus function operates similarly to
46       pj_init but takes a single string containing the
47       definition,  with each parameter prefixed with a
48       plus  sign.   For  example  "+proj=utm  +zone=11
49       +ellps=WGS84".
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51       Once  initialization is performed either forward
52       or inverse projections can be performed with the
53       returned  value  of pj_init used as the argument
54       proj.  The argument structure  projUV  values  u
55       and  v contain respective longitude and latitude
56       or x and y.  Latitude and longitude are in radi‐
57       ans.  If a projection operation fails, both ele‐
58       ments of projUV are set to HUGE_VAL (defined  in
59       math.h).
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61       Note:  all  projections have a forward mode, but
62       some do not have an inverse projection.  If  the
63       projection  does  not have an inverse the projPJ
64       structure element inv will be NULL.
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66       The pj_transform function may be used to  trans‐
67       form  points between the two provided coordinate
68       systems.  In addition to converting between car‐
69       tographic  projection coordinates and geographic
70       coordinates, this function also  takes  care  of
71       datum  shifts if possible between the source and
72       destination coordinate  system.   Unlike  pj_fwd
73       and  pj_inv it is also allowable for the coordi‐
74       nate system definitions (PJ *) to be  geographic
75       coordinate  systems  (defined as +proj=latlong).
76       The x, y and z arrays contain the  input  values
77       of  the points, and are replaced with the output
78       values.  The point_offset  should  indicate  the
79       spacing  the  of  x,y,z arrays, normally 1.  The
80       function returns zero on success, or  the  error
81       number (also in pj_errno) on failure.
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83       Memory  associated  with  the  projection may be
84       freed with pj_free.
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EXAMPLE

87       The following program reads latitude and  longi‐
88       tude  values in decimal degrees, performs Merca‐
89       tor projection with a Clarke 1866 ellipsoid  and
90       a 33° latitude of true scale and prints the pro‐
91       jected cartesian values in meters:
92       #include <proj_api.h>
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94       main(int argc, char **argv) {
95            char *args[] = { "proj=merc", "ellps=clrk66", "lat_ts=33" };
96            projUV p;
97            projPJ pj;
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99            if (!(pj = pj_init(3, args)))
100               exit(1);
101            while (scanf("%lf %lf", &p.v, &p.u) == 2) {
102               p.u *= DEG_TO_RAD;
103               p.v *= DEG_TO_RAD;
104               p = pj_fwd(p, pj);
105               printf("%.2f\t%.2f\n", p.u, p.v);
106            }
107            exit(0);
108       }
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LIBRARY

111       libproj.a - library of projections  and  support
112       procedures
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SEE ALSO

115       https://github.com/OSGeo/proj.4/wiki/ProjAPI,
116       proj(1),
117       Cartographic Projection Procedures for the  UNIX
118       Environment—A  User's  Manual,  (Evenden,  1990,
119       Open-file report 90-284).
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BUGS

122       A   list   of   known   bugs   can   found    at
123       https://github.com/OSGeo/proj.4/issues where new
124       bug reports can be submitted too.
125

HOME PAGE

127       http://proj4.org/
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131                  2001/04/05 Rel. 4.4       PJ_INIT(3U)
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