void eraAtioq	(	double	ri,
		double	di,
		eraASTROM *	astrom,
		double *	aob,
		double *	zob,
		double *	hob,
		double *	dob,
		double *	rob
	)

Definition at line 3 of file atioq.c.

References eraASTROM::cphi, eraASTROM::diurab, eraAnp(), eraC2s(), eraASTROM::eral, eraS2c(), eraASTROM::refa, eraASTROM::refb, eraASTROM::sphi, eraASTROM::xpl, and eraASTROM::ypl.

Referenced by eraAtco13(), eraAtio13(), and t_atioq().

{
/* Minimum cos(alt) and sin(alt) for refraction purposes */
   const double CELMIN = 1e-6;
   const double SELMIN = 0.05;

   double v[3], x, y, z, xhd, yhd, zhd, f, xhdt, yhdt, zhdt,
          xaet, yaet, zaet, azobs, r, tz, w, del, cosdel,
          xaeo, yaeo, zaeo, zdobs, hmobs, dcobs, raobs;

/*--------------------------------------------------------------------*/

/* CIRS RA,Dec to Cartesian -HA,Dec. */
   eraS2c(ri-astrom->eral, di, v);
   x = v[0];
   y = v[1];
   z = v[2];

/* Polar motion. */
   xhd = x + astrom->xpl*z;
   yhd = y - astrom->ypl*z;
   zhd = z - astrom->xpl*x + astrom->ypl*y;

/* Diurnal aberration. */
   f = ( 1.0 - astrom->diurab*yhd );
   xhdt = f * xhd;
   yhdt = f * ( yhd + astrom->diurab );
   zhdt = f * zhd;

/* Cartesian -HA,Dec to Cartesian Az,El (S=0,E=90). */
   xaet = astrom->sphi*xhdt - astrom->cphi*zhdt;
   yaet = yhdt;
   zaet = astrom->cphi*xhdt + astrom->sphi*zhdt;

/* Azimuth (N=0,E=90). */
   azobs = ( xaet != 0.0 || yaet != 0.0 ) ? atan2(yaet,-xaet) : 0.0;

/* ---------- */
/* Refraction */
/* ---------- */

/* Cosine and sine of altitude, with precautions. */
   r = sqrt(xaet*xaet + yaet*yaet);
   r = r > CELMIN ? r : CELMIN;
   z = zaet > SELMIN ? zaet : SELMIN;

/* A*tan(z)+B*tan^3(z) model, with Newton-Raphson correction. */
   tz = r/z;
   w = astrom->refb*tz*tz;
   del = ( astrom->refa + w ) * tz /
         ( 1.0 + ( astrom->refa + 3.0*w ) / ( z*z ) );

/* Apply the change, giving observed vector. */
   cosdel = 1.0 - del*del/2.0;
   f = cosdel - del*z/r;
   xaeo = xaet*f;
   yaeo = yaet*f;
   zaeo = cosdel*zaet + del*r;

/* Observed ZD. */
   zdobs = atan2(sqrt(xaeo*xaeo+yaeo*yaeo), zaeo);

/* Az/El vector to HA,Dec vector (both right-handed). */
   v[0] = astrom->sphi*xaeo + astrom->cphi*zaeo;
   v[1] = yaeo;
   v[2] = - astrom->cphi*xaeo + astrom->sphi*zaeo;

/* To spherical -HA,Dec. */
   eraC2s ( v, &hmobs, &dcobs );

/* Right ascension (with respect to CIO). */
   raobs = astrom->eral + hmobs;

/* Return the results. */
   *aob = eraAnp(azobs);
   *zob = zdobs;
   *hob = -hmobs;
   *dob = dcobs;
   *rob = eraAnp(raobs);

/* Finished. */

}

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