PJ_INIT(3)                                                   Library Functions Manual                                                   PJ_INIT(3)

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 success-
       ful 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 ar-
       gument 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 pro-
       jPJ 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  suc-
       cess, 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 33o 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	%.2f
", p.u, p.v);
            }
            exit(0);
       }

LIBRARY

       libproj.a - library of projections and support procedures

SEE ALSO

       http://proj.osgeo.org/ProjAPI, proj(1U),
       Cartographic Projection Procedures for the UNIX Environment--A User's Manual, (Evenden, 1990, Open-file report 90-284).

HOME PAGE

       http://proj.osgeo.org

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