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#define PJ_LIB__
#include <projects.h>
PROJ_HEAD(nell, "Nell") "\n\tPCyl., Sph.";
#define MAX_ITER 10
#define LOOP_TOL 1e-7
static XY s_forward (LP lp, PJ *P) { /* Spheroidal, forward */
XY xy = {0.0,0.0};
double k, V;
int i;
(void) P;
k = 2. * sin(lp.phi);
V = lp.phi * lp.phi;
lp.phi *= 1.00371 + V * (-0.0935382 + V * -0.011412);
for (i = MAX_ITER; i ; --i) {
lp.phi -= V = (lp.phi + sin(lp.phi) - k) /
(1. + cos(lp.phi));
if (fabs(V) < LOOP_TOL)
break;
}
xy.x = 0.5 * lp.lam * (1. + cos(lp.phi));
xy.y = lp.phi;
return xy;
}
static LP s_inverse (XY xy, PJ *P) { /* Spheroidal, inverse */
LP lp = {0.0,0.0};
lp.lam = 2. * xy.x / (1. + cos(xy.y));
lp.phi = aasin(P->ctx,0.5 * (xy.y + sin(xy.y)));
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) {
P->es = 0;
P->inv = s_inverse;
P->fwd = s_forward;
return P;
}
#ifndef PJ_SELFTEST
int pj_nell_selftest (void) {return 0;}
#else
int pj_nell_selftest (void) {
double tolerance_lp = 1e-10;
double tolerance_xy = 1e-7;
char s_args[] = {"+proj=nell +a=6400000 +lat_1=0.5 +lat_2=2"};
LP fwd_in[] = {
{ 2, 1},
{ 2,-1},
{-2, 1},
{-2,-1}
};
XY s_fwd_expect[] = {
{ 223385.132504695706, 111698.23644718733},
{ 223385.132504695706, -111698.23644718733},
{-223385.132504695706, 111698.23644718733},
{-223385.132504695706, -111698.23644718733},
};
XY inv_in[] = {
{ 200, 100},
{ 200,-100},
{-200, 100},
{-200,-100}
};
LP s_inv_expect[] = {
{ 0.00179049310989310567, 0.000895246554910125161},
{ 0.00179049310989310567, -0.000895246554910125161},
{-0.00179049310989310567, 0.000895246554910125161},
{-0.00179049310989310567, -0.000895246554910125161},
};
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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