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#define PJ_LIB__
#include <projects.h>
PROJ_HEAD(mbt_fps, "McBryde-Thomas Flat-Pole Sine (No. 2)") "\n\tCyl., Sph.";
#define MAX_ITER 10
#define LOOP_TOL 1e-7
#define C1 0.45503
#define C2 1.36509
#define C3 1.41546
#define C_x 0.22248
#define C_y 1.44492
#define C1_2 0.33333333333333333333333333
FORWARD(s_forward); /* spheroid */
double k, V, t;
int i;

k = C3 * sin(lp.phi);
for (i = MAX_ITER; i ; --i) {
t = lp.phi / C2;
lp.phi -= V = (C1 * sin(t) + sin(lp.phi) - k) /
(C1_2 * cos(t) + cos(lp.phi));
if (fabs(V) < LOOP_TOL)
break;
}
t = lp.phi / C2;
xy.x = C_x * lp.lam * (1. + 3. * cos(lp.phi)/cos(t) );
xy.y = C_y * sin(t);
return (xy);
}
INVERSE(s_inverse); /* spheroid */
double t, s;

lp.phi = C2 * (t = aasin(xy.y / C_y));
lp.lam = xy.x / (C_x * (1. + 3. * cos(lp.phi)/cos(t)));
lp.phi = aasin((C1 * sin(t) + sin(lp.phi)) / C3);
return (lp);
}
FREEUP; if (P) pj_dalloc(P); }
ENTRY0(mbt_fps) P->es = 0; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)
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