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#ifndef lint
static const char SCCSID[]="@(#)PJ_glabsgm.c 4.5 07/09/24 ??? ???";
#endif
#define PROJ_PARMS__ \
double lamc;\
double phic;\
double c;\
double n1;\
double n2;
#define PJ_LIB__
# include <projects.h>
PROJ_HEAD(glabsgm, "Gauss Laborde (Sphere Geometric Mean)")
"\n\tCyl, Sph&Ell\n\tlat_0= lon_0= k_0=";
FORWARD(s_forward); /* spheroid */
double L, Ls, sinLs1, Ls1;
L= P->n1*lp.lam;
Ls= P->c+P->n1*log(pj_tsfn(-1.0*lp.phi,-1.0*sin(lp.phi),P->e));
sinLs1= sin(L)/cosh(Ls);
Ls1= log(pj_tsfn(-1.0*asin(sinLs1),0.0,0.0));
xy.x= P->n2*P->ra*Ls1;
xy.y= P->n2*P->ra*atan(sinh(Ls)/cos(L));
return (xy);
}
INVERSE(s_inverse); /* spheroid */
double L, LC, sinC;
L= atan(sinh(xy.x*P->a/P->n2)/cos(xy.y*P->a/P->n2));
sinC= sin(xy.y*P->a/P->n2)/cosh(xy.x*P->a/P->n2);
LC= log(pj_tsfn(-1.0*asin(sinC),0.0,0.0));
lp.lam= L/P->n1;
lp.phi= -1.0*pj_phi2(exp((LC-P->c)/P->n1),P->e);
return (lp);
}
FREEUP; if (P) pj_dalloc(P); }
ENTRY0(glabsgm)
P->n1= sqrt(1.0+P->es*pow(cos(P->phi0),4.0)/(1.0-P->es));
P->phic= asin(sin(P->phi0)/P->n1);
P->c= log(pj_tsfn(-1.0*P->phic,0.0,0.0))
-P->n1*log(pj_tsfn(-1.0*P->phi0,-1.0*sin(P->phi0),P->e));
P->n2= P->k0*P->a*sqrt(1.0-P->es)/(1.0-P->es*sin(P->phi0)*sin(P->phi0));
P->y0-= P->n2*P->phic;
P->inv= s_inverse;
P->fwd= s_forward;
ENDENTRY(P)
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