NAME

       pj_init - initialize cartographic projection
       pj_init_plus - initialize cartographic projection
       pj_fwd - forward cartographic projection
       pj_inv - inverse cartographic projection
       pj_transform - transform between coordinate systems
       pj_free - de-initialize projection

SYNOPSIS

       #include <proj_api.h>

       projPJ pj_init(int argc, char **argv)

       projPJ pj_init_plus(const char *defn)

       projUV pj_fwd(projUV val, projPJ proj)

       projUV pj_inv(projUV val, projPJ proj)

       int pj_transform(projPJ src_cs, projPJ dst_cs, long point_count,
                        int point_offset, double *x, double *y, double *z)

       void pj_free(projPJ proj)

DESCRIPTION

       Procedure pj_init selects and initializes a cartographic projection with its argument control parameters.
       Argc is the number of elements in the  array  of  control  strings  argv  that  each  contain  individual
       cartographic  control  keyword  assignments  (+  proj  arguments).   The  list  must contain at least the
       proj=projection and Earth's radius or elliptical parameters.  If the initialization of the projection  is
       successful a valid address is returned otherwise a NULL value.

       The  pj_init_plus  function  operates  similarly  to  pj_init  but  takes  a single string containing the
       definition,  with  each  parameter  prefixed  with  a  plus  sign.   For  example   "+proj=utm   +zone=11
       +ellps=WGS84".

       Once initialization is performed either forward or inverse projections can be performed with the returned
       value of pj_init used as the argument proj.  The  argument  structure  projUV  values  u  and  v  contain
       respective  longitude  and  latitude or x and y.  Latitude and longitude are in radians.  If a projection
       operation fails, both elements of projUV are set to HUGE_VAL (defined in math.h).

       Note: all projections have a forward mode, but some do not have an inverse projection.  If the projection
       does not have an inverse the projPJ structure element inv will be NULL.

       The  pj_transform  function  may be used to transform points between the two provided coordinate systems.
       In addition to converting between cartographic projection coordinates and  geographic  coordinates,  this
       function  also  takes  care  of  datum  shifts  if possible between the source and destination coordinate
       system.  Unlike pj_fwd and pj_inv it is also allowable for the coordinate system definitions (PJ *) to be
       geographic coordinate systems (defined as +proj=latlong).  The x, y and z arrays contain the input values
       of the points, and are replaced with the output values.  The point_offset should indicate the spacing the
       of  x,y,z  arrays,  normally  1.   The  function  returns  zero  on success, or the error number (also in
       pj_errno) on failure.

       Memory associated with the projection may be freed with pj_free.

EXAMPLE

       The following program  reads  latitude  and  longitude  values  in  decimal  degrees,  performs  Mercator
       projection  with  a  Clarke  1866  ellipsoid  and  a  33° latitude of true scale and prints the projected
       cartesian values in meters:
       #include <proj_api.h>

       main(int argc, char **argv) {
            char *args[] = { "proj=merc", "ellps=clrk66", "lat_ts=33" };
            projUV p;
            projPJ pj;

            if (!(pj = pj_init(3, args)))
               exit(1);
            while (scanf("%lf %lf", &p.v, &p.u) == 2) {
               p.u *= DEG_TO_RAD;
               p.v *= DEG_TO_RAD;
               p = pj_fwd(p, pj);
               printf("%.2f\t%.2f\n", p.u, p.v);
            }
            exit(0);
       }

LIBRARY

       libproj.a - library of projections and support procedures

SEE ALSO

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

BUGS

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

HOME PAGE

       http://proj4.org/

                                               2001/04/05 Rel. 4.4                                    PJ_INIT(3)