/*
The Compact Miller projection was designed by Tom Patterson, US National
Park Service, in 2014. The polynomial equation was developed by Bojan
Savric and Bernhard Jenny, College of Earth, Ocean, and Atmospheric
Sciences, Oregon State University.
Port to PROJ.4 by Bojan Savric, 4 April 2016
*/

#define PJ_LIB_

#include <math.h>

#include "proj.h"
#include "proj_internal.h"

PROJ_HEAD(comill, "Compact Miller") "\n\tCyl, Sph";

#define K1 0.9902
#define K2 0.1604
#define K3 -0.03054
#define C1 K1
#define C2 (3 * K2)
#define C3 (5 * K3)
#define EPS 1e-11
#define MAX_Y (0.6000207669862655 * M_PI)
/* Not sure at all of the appropriate number for MAX_ITER... */
#define MAX_ITER 100

static PJ_XY comill_s_forward(PJ_LP lp, PJ *P) { /* Spheroidal, forward */
    PJ_XY xy = {0.0, 0.0};
    double lat_sq;

    (void)P; /* silence unused parameter warnings */

    lat_sq = lp.phi * lp.phi;
    xy.x = lp.lam;
    xy.y = lp.phi * (K1 + lat_sq * (K2 + K3 * lat_sq));
    return xy;
}

static PJ_LP comill_s_inverse(PJ_XY xy, PJ *P) { /* Spheroidal, inverse */
    PJ_LP lp = {0.0, 0.0};
    double yc, tol, y2, f, fder;
    int i;

    (void)P; /* silence unused parameter warnings */

    /* make sure y is inside valid range */
    if (xy.y > MAX_Y) {
        xy.y = MAX_Y;
    } else if (xy.y < -MAX_Y) {
        xy.y = -MAX_Y;
    }

    /* latitude */
    yc = xy.y;
    for (i = MAX_ITER; i; --i) { /* Newton-Raphson */
        y2 = yc * yc;
        f = (yc * (K1 + y2 * (K2 + K3 * y2))) - xy.y;
        fder = C1 + y2 * (C2 + C3 * y2);
        tol = f / fder;
        yc -= tol;
        if (fabs(tol) < EPS) {
            break;
        }
    }
    if (i == 0)
        proj_context_errno_set(
            P->ctx, PROJ_ERR_COORD_TRANSFM_OUTSIDE_PROJECTION_DOMAIN);
    lp.phi = yc;

    /* longitude */
    lp.lam = xy.x;

    return lp;
}

PJ *PROJECTION(comill) {
    P->es = 0;

    P->inv = comill_s_inverse;
    P->fwd = comill_s_forward;

    return P;
}
