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#define PJ_LIB__
#include <errno.h>
#include <math.h>
#include "proj.h"
#include "projects.h"
#include "proj_math.h"
PROJ_HEAD(gnom, "Gnomonic") "\n\tAzi, Sph";
#define EPS10 1.e-10
enum Mode {
N_POLE = 0,
S_POLE = 1,
EQUIT = 2,
OBLIQ = 3
};
struct pj_opaque {
double sinph0;
double cosph0;
enum Mode mode;
};
static XY s_forward (LP lp, PJ *P) { /* Spheroidal, forward */
XY xy = {0.0,0.0};
struct pj_opaque *Q = P->opaque;
double coslam, cosphi, sinphi;
sinphi = sin(lp.phi);
cosphi = cos(lp.phi);
coslam = cos(lp.lam);
switch (Q->mode) {
case EQUIT:
xy.y = cosphi * coslam;
break;
case OBLIQ:
xy.y = Q->sinph0 * sinphi + Q->cosph0 * cosphi * coslam;
break;
case S_POLE:
xy.y = - sinphi;
break;
case N_POLE:
xy.y = sinphi;
break;
}
if (xy.y <= EPS10) {
proj_errno_set(P, PJD_ERR_TOLERANCE_CONDITION);
return xy;
}
xy.x = (xy.y = 1. / xy.y) * cosphi * sin(lp.lam);
switch (Q->mode) {
case EQUIT:
xy.y *= sinphi;
break;
case OBLIQ:
xy.y *= Q->cosph0 * sinphi - Q->sinph0 * cosphi * coslam;
break;
case N_POLE:
coslam = - coslam;
/*-fallthrough*/
case S_POLE:
xy.y *= cosphi * coslam;
break;
}
return xy;
}
static LP s_inverse (XY xy, PJ *P) { /* Spheroidal, inverse */
LP lp = {0.0,0.0};
struct pj_opaque *Q = P->opaque;
double rh, cosz, sinz;
rh = hypot(xy.x, xy.y);
sinz = sin(lp.phi = atan(rh));
cosz = sqrt(1. - sinz * sinz);
if (fabs(rh) <= EPS10) {
lp.phi = P->phi0;
lp.lam = 0.;
} else {
switch (Q->mode) {
case OBLIQ:
lp.phi = cosz * Q->sinph0 + xy.y * sinz * Q->cosph0 / rh;
if (fabs(lp.phi) >= 1.)
lp.phi = lp.phi > 0. ? M_HALFPI : - M_HALFPI;
else
lp.phi = asin(lp.phi);
xy.y = (cosz - Q->sinph0 * sin(lp.phi)) * rh;
xy.x *= sinz * Q->cosph0;
break;
case EQUIT:
lp.phi = xy.y * sinz / rh;
if (fabs(lp.phi) >= 1.)
lp.phi = lp.phi > 0. ? M_HALFPI : - M_HALFPI;
else
lp.phi = asin(lp.phi);
xy.y = cosz * rh;
xy.x *= sinz;
break;
case S_POLE:
lp.phi -= M_HALFPI;
break;
case N_POLE:
lp.phi = M_HALFPI - lp.phi;
xy.y = -xy.y;
break;
}
lp.lam = atan2(xy.x, xy.y);
}
return lp;
}
PJ *PROJECTION(gnom) {
struct pj_opaque *Q = pj_calloc (1, sizeof (struct pj_opaque));
if (0==Q)
return pj_default_destructor (P, ENOMEM);
P->opaque = Q;
if (fabs(fabs(P->phi0) - M_HALFPI) < EPS10) {
Q->mode = P->phi0 < 0. ? S_POLE : N_POLE;
} else if (fabs(P->phi0) < EPS10) {
Q->mode = EQUIT;
} else {
Q->mode = OBLIQ;
Q->sinph0 = sin(P->phi0);
Q->cosph0 = cos(P->phi0);
}
P->inv = s_inverse;
P->fwd = s_forward;
P->es = 0.;
return P;
}
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