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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
static XY s_forward (LP lp, PJ *P) { /* Spheroidal, forward */
XY xy = {0.0,0.0};
(void) P;
xy.x = 0.5 * lp.lam * (1. + cos(lp.phi));
xy.y = 2.0 * (lp.phi - tan(0.5 *lp.phi));
return xy;
}
static LP s_inverse (XY xy, PJ *P) { /* Spheroidal, inverse */
LP lp = {0.0,0.0};
double V, c, p;
int i;
(void) P;
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. ? -M_HALFPI : M_HALFPI;
lp.lam = 2. * xy.x;
} else
lp.lam = 2. * xy.x / (1. + cos(lp.phi));
return lp;
}
static void *freeup_new (PJ *P) { /* Destructor */
if (0==P)
return 0;
return pj_dealloc(P);
}
static void freeup (PJ *P) {
freeup_new (P);
return;
}
PJ *PROJECTION(nell_h) {
P->es = 0.;
P->inv = s_inverse;
P->fwd = s_forward;
return P;
}
#ifndef PJ_SELFTEST
int pj_nell_h_selftest (void) {return 0;}
#else
int pj_nell_h_selftest (void) {
double tolerance_lp = 1e-10;
double tolerance_xy = 1e-7;
char s_args[] = {"+proj=nell_h +a=6400000 +lat_1=0.5 +lat_2=2"};
LP fwd_in[] = {
{ 2, 1},
{ 2,-1},
{-2, 1},
{-2,-1}
};
XY s_fwd_expect[] = {
{ 223385.131640952837, 111698.236533561678},
{ 223385.131640952837, -111698.236533561678},
{-223385.131640952837, 111698.236533561678},
{-223385.131640952837, -111698.236533561678},
};
XY inv_in[] = {
{ 200, 100},
{ 200,-100},
{-200, 100},
{-200,-100}
};
LP s_inv_expect[] = {
{ 0.00179049310989310567, 0.000895246554910125378},
{ 0.00179049310989310567, -0.000895246554910125378},
{-0.00179049310989310567, 0.000895246554910125378},
{-0.00179049310989310567, -0.000895246554910125378},
};
return pj_generic_selftest (0, s_args, tolerance_xy, tolerance_lp, 4, 4, fwd_in, 0, s_fwd_expect, inv_in, 0, s_inv_expect);
}
#endif
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