Application: gvSIG desktop

/* 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;

}