void palRefz	(	double	zu,
		double	refa,
		double	refb,
		double *	zr
	)

Definition at line 136 of file palRefz.c.

References DMIN, PAL__DD2R, PAL__DR2D, and t.

Referenced by palAopqk(), and t_ref().

                                                                 {

  /* Constants */

  /* Largest usable ZD (deg) */
  const double D93 = 93.0;

  /* ZD at which one model hands over to the other (radians) */
  const double Z83 = 83.0 * PAL__DD2R;

  /* coefficients for high ZD model (used beyond ZD 83 deg) */
  const double C1 = +0.55445;
  const double C2 = -0.01133;
  const double C3 = +0.00202;
  const double C4 = +0.28385;
  const double C5 = +0.02390;

  /* High-ZD-model prefiction (deg) for that point */
  const double REF83 = (C1+C2*7.0+C3*49.0)/(1.0+C4*7.0+C5*49.0);

  double zu1,zl,s,c,t,tsq,tcu,ref,e,e2;

  /*  perform calculations for zu or 83 deg, whichever is smaller */
  zu1 = DMIN(zu,Z83);

  /*  functions of ZD */
  zl = zu1;
  s = sin(zl);
  c = cos(zl);
  t = s/c;
  tsq = t*t;
  tcu = t*tsq;

  /*  refracted zd (mathematically to better than 1 mas at 70 deg) */
  zl = zl-(refa*t+refb*tcu)/(1.0+(refa+3.0*refb*tsq)/(c*c));

  /*  further iteration */
  s = sin(zl);
  c = cos(zl);
  t = s/c;
  tsq = t*t;
  tcu = t*tsq;
  ref = zu1-zl+
    (zl-zu1+refa*t+refb*tcu)/(1.0+(refa+3.0*refb*tsq)/(c*c));

  /*  special handling for large zu */
  if (zu > zu1) {
    e = 90.0-DMIN(D93,zu*PAL__DR2D);
    e2 = e*e;
    ref = (ref/REF83)*(C1+C2*e+C3*e2)/(1.0+C4*e+C5*e2);
  }

  /*  return refracted zd */
  *zr = zu-ref;

}

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