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/* determine latitude angle phi-2 */
#ifndef lint
static const char SCCSID[]="@(#)pj_phi2.c 4.3 93/06/12 GIE REL";
#endif
#include <projects.h>
#define HALFPI 1.5707963267948966
#define TOL 1.0e-10
#define N_ITER 15
double
pj_phi2(double ts, double e) {
double eccnth, Phi, con, dphi;
int i;
eccnth = .5 * e;
Phi = HALFPI - 2. * atan (ts);
i = N_ITER;
do {
con = e * sin (Phi);
dphi = HALFPI - 2. * atan (ts * pow((1. - con) /
(1. + con), eccnth)) - Phi;
Phi += dphi;
} while ( fabs(dphi) > TOL && --i);
if (i <= 0)
pj_errno = -18;
return Phi;
}
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