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#ifndef lint
static const char SCCSID[]="@(#)PJ_airy.c 4.1 94/02/15 GIE REL";
#endif
#define PROJ_PARMS__ \
double p_halfpi; \
double sinph0; \
double cosph0; \
double Cb; \
int mode; \
int no_cut; /* do not cut at hemisphere limit */
#define PJ_LIB__
#include <projects.h>
PROJ_HEAD(airy, "Airy") "\n\tMisc Sph, no inv.\n\tno_cut lat_b=";
# define EPS 1.e-10
# define N_POLE 0
# define S_POLE 1
# define EQUIT 2
# define OBLIQ 3
FORWARD(s_forward); /* spheroid */
double sinlam, coslam, cosphi, sinphi, t, s, Krho, cosz;
sinlam = sin(lp.lam);
coslam = cos(lp.lam);
switch (P->mode) {
case EQUIT:
case OBLIQ:
sinphi = sin(lp.phi);
cosphi = cos(lp.phi);
cosz = cosphi * coslam;
if (P->mode == OBLIQ)
cosz = P->sinph0 * sinphi + P->cosph0 * cosz;
if (!P->no_cut && cosz < -EPS)
F_ERROR;
if (fabs(s = 1. - cosz) > EPS) {
t = 0.5 * (1. + cosz);
Krho = -log(t)/s - P->Cb / t;
} else
Krho = 0.5 - P->Cb;
xy.x = Krho * cosphi * sinlam;
if (P->mode == OBLIQ)
xy.y = Krho * (P->cosph0 * sinphi -
P->sinph0 * cosphi * coslam);
else
xy.y = Krho * sinphi;
break;
case S_POLE:
case N_POLE:
lp.phi = fabs(P->p_halfpi - lp.phi);
if (!P->no_cut && (lp.phi - EPS) > HALFPI)
F_ERROR;
if ((lp.phi *= 0.5) > EPS) {
t = tan(lp.phi);
Krho = -2.*(log(cos(lp.phi)) / t + t * P->Cb);
xy.x = Krho * sinlam;
xy.y = Krho * coslam;
if (P->mode == N_POLE)
xy.y = -xy.y;
} else
xy.x = xy.y = 0.;
}
return (xy);
}
FREEUP; if (P) pj_dalloc(P); }
ENTRY0(airy)
double beta;
P->no_cut = pj_param(P->params, "bno_cut").i;
beta = 0.5 * (HALFPI - pj_param(P->params, "rlat_b").f);
if (fabs(beta) < EPS)
P->Cb = -0.5;
else {
P->Cb = 1./tan(beta);
P->Cb *= P->Cb * log(cos(beta));
}
if (fabs(fabs(P->phi0) - HALFPI) < EPS)
if (P->phi0 < 0.) {
P->p_halfpi = -HALFPI;
P->mode = S_POLE;
} else {
P->p_halfpi = HALFPI;
P->mode = N_POLE;
}
else {
if (fabs(P->phi0) < EPS)
P->mode = EQUIT;
else {
P->mode = OBLIQ;
P->sinph0 = sin(P->phi0);
P->cosph0 = cos(P->phi0);
}
}
P->fwd = s_forward;
P->es = 0.;
ENDENTRY(P)
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