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/*
** 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(vandg4, "van der Grinten IV") "\n\tMisc Sph, no inv.";
#define TOL 1e-10
#define TWORPI 0.63661977236758134308
FORWARD(s_forward); /* spheroid */
double x1, t, bt, ct, ft, bt2, ct2, dt, dt2;
(void) P; /* avoid warning */
if (fabs(lp.phi) < TOL) {
xy.x = lp.lam;
xy.y = 0.;
} else if (fabs(lp.lam) < TOL || fabs(fabs(lp.phi) - HALFPI) < TOL) {
xy.x = 0.;
xy.y = lp.phi;
} else {
bt = fabs(TWORPI * lp.phi);
bt2 = bt * bt;
ct = 0.5 * (bt * (8. - bt * (2. + bt2)) - 5.)
/ (bt2 * (bt - 1.));
ct2 = ct * ct;
dt = TWORPI * lp.lam;
dt = dt + 1. / dt;
dt = sqrt(dt * dt - 4.);
if ((fabs(lp.lam) - HALFPI) < 0.) dt = -dt;
dt2 = dt * dt;
x1 = bt + ct; x1 *= x1;
t = bt + 3.*ct;
ft = x1 * (bt2 + ct2 * dt2 - 1.) + (1.-bt2) * (
bt2 * (t * t + 4. * ct2) +
ct2 * (12. * bt * ct + 4. * ct2) );
x1 = (dt*(x1 + ct2 - 1.) + 2.*sqrt(ft)) /
(4.* x1 + dt2);
xy.x = HALFPI * x1;
xy.y = HALFPI * sqrt(1. + dt * fabs(x1) - x1 * x1);
if (lp.lam < 0.) xy.x = -xy.x;
if (lp.phi < 0.) xy.y = -xy.y;
}
return (xy);
}
FREEUP; if (P) free(P); }
ENTRY0(vandg4) P->es = 0.; P->fwd = s_forward; ENDENTRY(P)
/*
** Log: proj_vandg4.c
** Revision 3.1 2006/01/11 01:38:18 gie
** Initial
**
*/
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