/*
** libproj -- library of cartographic projections
**
** Copyright (c) 2003, 2006   Gerald I. Evenden
*/
static const char
LIBPROJ_ID[] = "Id";
/*
** Permission is hereby granted, free of charge, to any person obtaining
** a copy of this software and associated documentation files (the
** "Software"), to deal in the Software without restriction, including
** without limitation the rights to use, copy, modify, merge, publish,
** distribute, sublicense, and/or sell copies of the Software, and to
** permit persons to whom the Software is furnished to do so, subject to
** the following conditions:
**
** The above copyright notice and this permission notice shall be
** included in all copies or substantial portions of the Software.
**
** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
** SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#define PROJ_LIB__
#include  <lib_proj.h>
PROJ_HEAD(eck4, "Eckert IV") "\n\tPCyl, Sph.";
#define C_x  .42223820031577120149
#define C_y  1.32650042817700232218
#define RC_y  .75386330736002178205
#define C_p  3.57079632679489661922
#define RC_p  .28004957675577868795
#define EPS  1e-7
#define NITER  6
FORWARD(s_forward); /* spheroid */
  double p, V, s, c;
  int i;
  (void) P; /* avoid warning */

  p = C_p * sin(lp.phi);
  V = lp.phi * lp.phi;
  lp.phi *= 0.895168 + V * ( 0.0218849 + V * 0.00826809 );
  for (i = NITER; i ; --i) {
    c = cos(lp.phi);
    s = sin(lp.phi);
    lp.phi -= V = (lp.phi + s * (c + 2.) - p) /
      (1. + c * (c + 2.) - s * s);
    if (fabs(V) < EPS)
      break;
  }
  if (!i) {
    xy.x = C_x * lp.lam;
    xy.y = lp.phi < 0. ? -C_y : C_y;
  } else {
    xy.x = C_x * lp.lam * (1. + cos(lp.phi));
    xy.y = C_y * sin(lp.phi);
  }
  return (xy);
}
INVERSE(s_inverse); /* spheroid */
  double c;
  (void) P; /* avoid warning */

  lp.phi = proj_asin(xy.y / C_y);
  lp.lam = xy.x / (C_x * (1. + (c = cos(lp.phi))));
  lp.phi = proj_asin((lp.phi + sin(lp.phi) * (c + 2.)) / C_p);
  return (lp);
}
FREEUP; if (P) free(P); }
ENTRY0(eck4); P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)
/*
** Log: proj_eck4.c
** Revision 3.1  2006/01/11 01:38:18  gie
** Initial
**
*/