/Proj4/PJ_mbt_fps.c

 1#ifndef lint
 2static const char SCCSID[]="@(#)PJ_mbt_fps.c	4.1	94/02/15	GIE	REL";
 3#endif
 4#define PJ_LIB__
 5#include	"projects.h"
 6PROJ_HEAD(mbt_fps, "McBryde-Thomas Flat-Pole Sine (No. 2)") "\n\tCyl., Sph.";
 7#define MAX_ITER	10
 8#define LOOP_TOL	1e-7
 9#define C1 0.45503
10#define C2 1.36509
11#define C3 1.41546
12#define C_x 0.22248
13#define C_y 1.44492
14#define C1_2 0.33333333333333333333333333
15FORWARD(s_forward); /* spheroid */
16	double k, V, t;
17	int i;
18
19	k = C3 * sin(lp.phi);
20	for (i = MAX_ITER; i ; --i) {
21		t = lp.phi / C2;
22		lp.phi -= V = (C1 * sin(t) + sin(lp.phi) - k) /
23			(C1_2 * cos(t) + cos(lp.phi));
24		if (fabs(V) < LOOP_TOL)
25			break;
26	}
27	t = lp.phi / C2;
28	xy.x = C_x * lp.lam * (1. + 3. * cos(lp.phi)/cos(t) );
29	xy.y = C_y * sin(t);
30	return (xy);
31}
32INVERSE(s_inverse); /* spheroid */
33	double t, s;
34
35	lp.phi = C2 * (t = aasin(xy.y / C_y));
36	lp.lam = xy.x / (C_x * (1. + 3. * cos(lp.phi)/cos(t)));
37	lp.phi = aasin((C1 * sin(t) + sin(lp.phi)) / C3);
38	return (lp);
39}
40FREEUP; if (P) pj_dalloc(P); }
41ENTRY0(mbt_fps) P->es = 0; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)