2
static const char SCCSID[]="@(#)PJ_eck4.c 4.1 94/02/15 GIE REL";
6
PROJ_HEAD(eck4, "Eckert IV") "\n\tPCyl, Sph.";
7
#define C_x .42223820031577120149
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#define C_y 1.32650042817700232218
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#define RC_y .75386330736002178205
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#define C_p 3.57079632679489661922
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#define RC_p .28004957675577868795
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FORWARD(s_forward); /* spheroid */
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p = C_p * sin(lp.phi);
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lp.phi *= 0.895168 + V * ( 0.0218849 + V * 0.00826809 );
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for (i = NITER; i ; --i) {
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lp.phi -= V = (lp.phi + s * (c + 2.) - p) /
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(1. + c * (c + 2.) - s * s);
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xy.y = lp.phi < 0. ? -C_y : C_y;
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xy.x = C_x * lp.lam * (1. + cos(lp.phi));
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xy.y = C_y * sin(lp.phi);
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INVERSE(s_inverse); /* spheroid */
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lp.phi = aasin(xy.y / C_y);
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lp.lam = xy.x / (C_x * (1. + (c = cos(lp.phi))));
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lp.phi = aasin((lp.phi + sin(lp.phi) * (c + 2.)) / C_p);
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FREEUP; if (P) pj_dalloc(P); }
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ENTRY0(eck4); P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)