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#ifndef lint
static const char SCCSID[]="@(#)PJ_gstmerc.c 4.6 08/07/28 DGR IGN";
#endif
#define PROJ_PARMS__ \
double lamc;\
double phic;\
double c;\
double n1;\
double n2;\
double XS;\
double YS;
#define PJ_LIB__
# include <projects.h>
PROJ_HEAD(gstmerc, "Gauss-Schreiber Transverse Mercator (aka Gauss-Laborde Reunion)")
"\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->XS + P->n2*Ls1)*P->ra;
xy.y= (P->YS + P->n2*atan(sinh(Ls)/cos(L)))*P->ra;
return (xy);
}
INVERSE(s_inverse); /* spheroid */
double L, LC, sinC;
L= atan(sinh((xy.x - P->XS)*P->a/P->n2)/cos((xy.y - P->YS)*P->a/P->n2));
sinC= sin((xy.y - P->YS)*P->a/P->n2)/cosh((xy.x - P->XS)*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(gstmerc)
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->XS= 0;
P->YS= -1.0*P->n2*P->phic;
P->inv= s_inverse;
P->fwd= s_forward;
ENDENTRY(P)
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