Application: gvSIG desktop

#ifndef lint

static const char SCCSID[]="@(#)PJ_eck4.c        4.1        94/02/15        GIE        REL";

#endif

#define PJ_LIB__

#include        <projects.h>

PROJ_HEAD(eck4, "Eckert IV") "\n\tPCyl, Sph.";

#define C_x        .42223820031577120149

#define C_y        1.32650042817700232218

#define RC_y        .75386330736002178205

#define C_p        3.57079632679489661922

#define RC_p        .28004957675577868795

#define EPS        1e-7

#define NITER        6

FORWARD(s_forward); /* spheroid */

        double p, V, s, c;

        int i;

        p = C_p * sin(lp.phi);

        V = lp.phi * lp.phi;

        lp.phi *= 0.895168 + V * ( 0.0218849 + V * 0.00826809 );

        for (i = NITER; i ; --i) {

                c = cos(lp.phi);

                s = sin(lp.phi);

                lp.phi -= V = (lp.phi + s * (c + 2.) - p) /

                        (1. + c * (c + 2.) - s * s);

                if (fabs(V) < EPS)

                        break;

        }

        if (!i) {

                xy.x = C_x * lp.lam;

                xy.y = lp.phi < 0. ? -C_y : C_y;

        } else {

                xy.x = C_x * lp.lam * (1. + cos(lp.phi));

                xy.y = C_y * sin(lp.phi);

        }

        return (xy);

}

INVERSE(s_inverse); /* spheroid */

        double c;

        lp.phi = aasin(xy.y / C_y);

        lp.lam = xy.x / (C_x * (1. + (c = cos(lp.phi))));

        lp.phi = aasin((lp.phi + sin(lp.phi) * (c + 2.)) / C_p);

        return (lp);

}

FREEUP; if (P) pj_dalloc(P); }

ENTRY0(eck4); P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)