PJ_eck2.c

#define PJ_LIB__
# include	<projects.h>
PROJ_HEAD(eck2, "Eckert II") "\n\tPCyl. Sph.";
#define FXC	0.46065886596178063902
#define FYC	1.44720250911653531871
#define C13	0.33333333333333333333
#define ONEEPS	1.0000001
FORWARD(s_forward); /* spheroid */
	xy.x = FXC * lp.lam * (xy.y = sqrt(4. - 3. * sin(fabs(lp.phi))));
	xy.y = FYC * (2. - xy.y);
	if ( lp.phi < 0.) xy.y = -xy.y;
	return (xy);
}
INVERSE(s_inverse); /* spheroid */
	lp.lam = xy.x / (FXC * ( lp.phi = 2. - fabs(xy.y) / FYC) );
	lp.phi = (4. - lp.phi * lp.phi) * C13;
	if (fabs(lp.phi) >= 1.) {
		if (fabs(lp.phi) > ONEEPS)	I_ERROR
		else
			lp.phi = lp.phi < 0. ? -HALFPI : HALFPI;
	} else
		lp.phi = asin(lp.phi);
	if (xy.y < 0)
		lp.phi = -lp.phi;
	return (lp);
}
FREEUP; if (P) pj_dalloc(P); }
ENTRY0(eck2); P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)