EVOLUTION-MANAGER

Edit File: PJ_mod_ster.c

/* based upon Snyder and Linck, USGS-NMD */
#define PJ_LIB__
#include <errno.h>
#include "projects.h"
#include "proj_math.h"

PROJ_HEAD(mil_os, "Miller Oblated Stereographic") "\n\tAzi(mod)";
PROJ_HEAD(lee_os, "Lee Oblated Stereographic") "\n\tAzi(mod)";
PROJ_HEAD(gs48, "Mod. Stereographic of 48 U.S.") "\n\tAzi(mod)";
PROJ_HEAD(alsk, "Mod. Stereographic of Alaska") "\n\tAzi(mod)";
PROJ_HEAD(gs50, "Mod. Stereographic of 50 U.S.") "\n\tAzi(mod)";

#define EPSLN 1e-12

struct pj_opaque {
    const COMPLEX *zcoeff; \
    double  cchio, schio; \
    int     n;
};

static XY e_forward (LP lp, PJ *P) {          /* Ellipsoidal, forward */
    XY xy = {0.0,0.0};
    struct pj_opaque *Q = P->opaque;
    double sinlon, coslon, esphi, chi, schi, cchi, s;
    COMPLEX p;

sinlon = sin(lp.lam);
    coslon = cos(lp.lam);
    esphi = P->e * sin(lp.phi);
    chi = 2. * atan(tan((M_HALFPI + lp.phi) * .5) *
        pow((1. - esphi) / (1. + esphi), P->e * .5)) - M_HALFPI;
    schi = sin(chi);
    cchi = cos(chi);
    s = 2. / (1. + Q->schio * schi + Q->cchio * cchi * coslon);
    p.r = s * cchi * sinlon;
    p.i = s * (Q->cchio * schi - Q->schio * cchi * coslon);
    p = pj_zpoly1(p, Q->zcoeff, Q->n);
    xy.x = p.r;
    xy.y = p.i;

return xy;
}

static LP e_inverse (XY xy, PJ *P) {          /* Ellipsoidal, inverse */
    LP lp = {0.0,0.0};
    struct pj_opaque *Q = P->opaque;
    int nn;
    COMPLEX p, fxy, fpxy, dp;
    double den, rh = 0.0, z, sinz = 0.0, cosz = 0.0, chi, phi = 0.0, esphi;

p.r = xy.x;
    p.i = xy.y;
    for (nn = 20; nn ;--nn) {
        fxy = pj_zpolyd1(p, Q->zcoeff, Q->n, &fpxy);
        fxy.r -= xy.x;
        fxy.i -= xy.y;
        den = fpxy.r * fpxy.r + fpxy.i * fpxy.i;
        dp.r = -(fxy.r * fpxy.r + fxy.i * fpxy.i) / den;
        dp.i = -(fxy.i * fpxy.r - fxy.r * fpxy.i) / den;
        p.r += dp.r;
        p.i += dp.i;
        if ((fabs(dp.r) + fabs(dp.i)) <= EPSLN)
            break;
    }
    if (nn) {
        rh = hypot(p.r, p.i);
        z = 2. * atan(.5 * rh);
        sinz = sin(z);
        cosz = cos(z);
        lp.lam = P->lam0;
        if (fabs(rh) <= EPSLN) {
            /* if we end up here input coordinates were (0,0).
             * pj_inv() adds P->lam0 to lp.lam, this way we are
             * sure to get the correct offset */
            lp.lam = 0.0;
            lp.phi = P->phi0;
            return lp;
        }
        chi = aasin(P->ctx, cosz * Q->schio + p.i * sinz * Q->cchio / rh);
        phi = chi;
        for (nn = 20; nn ;--nn) {
            double dphi;
            esphi = P->e * sin(phi);
            dphi = 2. * atan(tan((M_HALFPI + chi) * .5) *
                pow((1. + esphi) / (1. - esphi), P->e * .5)) - M_HALFPI - phi;
            phi += dphi;
            if (fabs(dphi) <= EPSLN)
                break;
        }
    }
    if (nn) {
        lp.phi = phi;
        lp.lam = atan2(p.r * sinz, rh * Q->cchio * cosz - p.i *
            Q->schio * sinz);
    } else
        lp.lam = lp.phi = HUGE_VAL;
    return lp;
}

static PJ *setup(PJ *P) { /* general initialization */
    struct pj_opaque *Q = P->opaque;
    double esphi, chio;

if (P->es != 0.0) {
        esphi = P->e * sin(P->phi0);
        chio = 2. * atan(tan((M_HALFPI + P->phi0) * .5) *
            pow((1. - esphi) / (1. + esphi), P->e * .5)) - M_HALFPI;
    } else
        chio = P->phi0;
    Q->schio = sin(chio);
    Q->cchio = cos(chio);
    P->inv = e_inverse;
    P->fwd = e_forward;

return P;
}

/* Miller Oblated Stereographic */
PJ *PROJECTION(mil_os) {
    static const COMPLEX AB[] = {
        {0.924500, 0.},
        {0.,       0.},
        {0.019430, 0.}
    };