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#define PJ_LIB__
# include <projects.h>
PROJ_HEAD(nell_h, "Nell-Hammer") "\n\tPCyl., Sph.";
#define NITER 9
#define EPS 1e-7
FORWARD(s_forward); /* spheroid */
xy.x = 0.5 * lp.lam * (1. + cos(lp.phi));
xy.y = 2.0 * (lp.phi - tan(0.5 *lp.phi));
return (xy);
}
INVERSE(s_inverse); /* spheroid */
double V, c, p;
int i;
p = 0.5 * xy.y;
for (i = NITER; i ; --i) {
c = cos(0.5 * lp.phi);
lp.phi -= V = (lp.phi - tan(lp.phi/2) - p)/(1. - 0.5/(c*c));
if (fabs(V) < EPS)
break;
}
if (!i) {
lp.phi = p < 0. ? -HALFPI : HALFPI;
lp.lam = 2. * xy.x;
} else
lp.lam = 2. * xy.x / (1. + cos(lp.phi));
return (lp);
}
FREEUP; if (P) pj_dalloc(P); }
ENTRY0(nell_h) P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)
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