PJ_INIT(3U)PJ_INIT(3U)NAMEpj_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,
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 pro
jection is successful a valid address is returned other
wise 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 radi
ans. 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 desti
nation 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 function returns zero on success, or the er
ror 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 degress, 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 ALSOproj(1U),
Cartographic Projection Procedures for the UNIX Environ_
ment--A User's Manual, (Evenden, 1990, Open-file report
90-284).
HOME PAGE
http://www.remotesensing.org/proj
2001/04/05 Rel. 4.4 PJ_INIT(3U)
