Application: gvSIG desktop » gvSIG 3D

#ifndef lint

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

#endif

#define PJ_LIB__

# include        <projects.h>

PROJ_HEAD(nell_h, "Nell-Hammer") "\n\tPCyl., Sph.";

#define NITER 9

#define EPS 1e-7

FORWARD(s_forward); /* spheroid */

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

        xy.y = 2.0 * (lp.phi - tan(0.5 *lp.phi));

        return (xy);

}

INVERSE(s_inverse); /* spheroid */

        double V, c, p;

        int i;

        p = 0.5 * xy.y;

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

                c = cos(0.5 * lp.phi);

                lp.phi -= V = (lp.phi - tan(lp.phi/2) - p)/(1. - 0.5/(c*c));

                if (fabs(V) < EPS)

                        break;

        }

        if (!i) {

                lp.phi = p < 0. ? -HALFPI : HALFPI;

                lp.lam = 2. * xy.x;

        } else

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

        return (lp);

}

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

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