#include <math.h>

#include "proj.h"

#include "proj_internal.h"

PROJ_HEAD(tcea, "Transverse Cylindrical Equal Area") "\n\tCyl, Sph";

static PJ_XY tcea_s_forward(PJ_LP lp, PJ *P) { /* Spheroidal, forward */

    PJ_XY xy = {0.0, 0.0};

    xy.x = cos(lp.phi) * sin(lp.lam) / P->k0;

    xy.y = P->k0 * (atan2(tan(lp.phi), cos(lp.lam)) - P->phi0);

    return xy;

}

static PJ_LP tcea_s_inverse(PJ_XY xy, PJ *P) { /* Spheroidal, inverse */

    PJ_LP lp = {0.0, 0.0};

    double t;

    xy.y = xy.y / P->k0 + P->phi0;

    xy.x *= P->k0;

    t = sqrt(1. - xy.x * xy.x);

    lp.phi = asin(t * sin(xy.y));

    lp.lam = atan2(xy.x, t * cos(xy.y));

    return lp;

}

PJ *PJ_PROJECTION(tcea) {

    P->inv = tcea_s_inverse;

    P->fwd = tcea_s_forward;

    P->es = 0.;

    return P;

}