#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)
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 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.
#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);
}