Application: gvSIG desktop

#ifndef lint

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

#endif

#define PJ_LIB__

#include        <projects.h>

PROJ_HEAD(nell, "Nell") "\n\tPCyl., Sph.";

#define MAX_ITER        10

#define LOOP_TOL        1e-7

FORWARD(s_forward); /* spheroid */

        double k, V;

        int i;

        k = 2. * sin(lp.phi);

        V = lp.phi * lp.phi;

        lp.phi *= 1.00371 + V * (-0.0935382 + V * -0.011412);

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

                lp.phi -= V = (lp.phi + sin(lp.phi) - k) /

                        (1. + cos(lp.phi));

                if (fabs(V) < LOOP_TOL)

                        break;

        }

        xy.x = 0.5 * lp.lam * (1. + cos(lp.phi));

        xy.y = lp.phi;

        return (xy);

}

INVERSE(s_inverse); /* spheroid */

        double th, s;

        lp.lam = 2. * xy.x / (1. + cos(xy.y));

        lp.phi = aasin(0.5 * (xy.y + sin(xy.y)));

        return (lp);

}

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

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