EVOLUTION-MANAGER

Edit File: PJ_moll.c

#define PJ_LIB__

#include <errno.h>
#include <math.h>

#include "projects.h"

PROJ_HEAD(moll, "Mollweide") "\n\tPCyl., Sph.";
PROJ_HEAD(wag4, "Wagner IV") "\n\tPCyl., Sph.";
PROJ_HEAD(wag5, "Wagner V") "\n\tPCyl., Sph.";

#define MAX_ITER    10
#define LOOP_TOL    1e-7

struct pj_opaque {
    double  C_x, C_y, C_p;
};

static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
    XY xy = {0.0,0.0};
    struct pj_opaque *Q = P->opaque;
    double k, V;
    int i;

k = Q->C_p * sin(lp.phi);
    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;
    }
    if (!i)
        lp.phi = (lp.phi < 0.) ? -M_HALFPI : M_HALFPI;
    else
        lp.phi *= 0.5;
    xy.x = Q->C_x * lp.lam * cos(lp.phi);
    xy.y = Q->C_y * sin(lp.phi);
    return xy;
}

static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
    LP lp = {0.0,0.0};
    struct pj_opaque *Q = P->opaque;
    lp.phi = aasin(P->ctx, xy.y / Q->C_y);
    lp.lam = xy.x / (Q->C_x * cos(lp.phi));
        if (fabs(lp.lam) < M_PI) {
            lp.phi += lp.phi;
            lp.phi = aasin(P->ctx, (lp.phi + sin(lp.phi)) / Q->C_p);
        } else {
            lp.lam = lp.phi = HUGE_VAL;
        }
    return lp;
}

static PJ * setup(PJ *P, double p) {
    struct pj_opaque *Q = P->opaque;
    double r, sp, p2 = p + p;

P->es = 0;
    sp = sin(p);
    r = sqrt(M_TWOPI * sp / (p2 + sin(p2)));

Q->C_x = 2. * r / M_PI;
    Q->C_y = r / sp;
    Q->C_p = p2 + sin(p2);

P->inv = s_inverse;
    P->fwd = s_forward;
    return P;
}

PJ *PROJECTION(moll) {
    struct pj_opaque *Q = pj_calloc (1, sizeof (struct pj_opaque));
    if (0==Q)
        return pj_default_destructor (P, ENOMEM);
    P->opaque = Q;

return setup(P, M_HALFPI);
}

PJ *PROJECTION(wag4) {
    struct pj_opaque *Q = pj_calloc (1, sizeof (struct pj_opaque));
    if (0==Q)
        return pj_default_destructor (P, ENOMEM);
    P->opaque = Q;

return setup(P, M_PI/3.);
}

PJ *PROJECTION(wag5) {
    struct pj_opaque *Q = pj_calloc (1, sizeof (struct pj_opaque));
    if (0==Q)
        return pj_default_destructor (P, ENOMEM);
    P->opaque = Q;

P->es = 0;
    Q->C_x = 0.90977;
    Q->C_y = 1.65014;
    Q->C_p = 3.00896;

P->inv = s_inverse;
    P->fwd = s_forward;

return P;
}