void palAltaz	(	double	ha,
		double	dec,
		double	phi,
		double *	az,
		double *	azd,
		double *	azdd,
		double *	el,
		double *	eld,
		double *	eldd,
		double *	pa,
		double *	pad,
		double *	padd
	)

Definition at line 132 of file palAltaz.c.

References PAL__D2PI, and PAL__DPI.

Referenced by t_altaz().

                                                   {

  const double TINY = 1E-30;

  double sh,ch,sd,cd,sp,cp,chcd,sdcp,x,y,z,rsq,r,a,e,c,s,
    q,qd,ad,ed,edr,add,edd,qdd;


  /*  Useful functions */
  sh=sin(ha);
  ch=cos(ha);
  sd=sin(dec);
  cd=cos(dec);
  sp=sin(phi);
  cp=cos(phi);
  chcd=ch*cd;
  sdcp=sd*cp;
  x=-chcd*sp+sdcp;
  y=-sh*cd;
  z=chcd*cp+sd*sp;
  rsq=x*x+y*y;
  r=sqrt(rsq);

  /*  Azimuth and elevation */
  if (rsq == 0.0) {
    a=0.0;
  } else {
    a=atan2(y,x);
  }
  if (a < 0.0) a += PAL__D2PI;
  e=atan2(z,r);

  /*  Parallactic angle */
  c=cd*sp-ch*sdcp;
  s=sh*cp;
  if (c*c+s*s > 0) {
    q=atan2(s,c);
  } else {
    q= PAL__DPI - ha;
  }

  /*  Velocities and accelerations (clamped at zenith/nadir) */
  if (rsq < TINY) {
    rsq=TINY;
    r=sqrt(rsq);
  }
  qd=-x*cp/rsq;
  ad=sp+z*qd;
  ed=cp*y/r;
  edr=ed/r;
  add=edr*(z*sp+(2.0-rsq)*qd);
  edd=-r*qd*ad;
  qdd=edr*(sp+2.0*z*qd);

  /*  Results */
  *az=a;
  *azd=ad;
  *azdd=add;
  *el=e;
  *eld=ed;
  *eldd=edd;
  *pa=q;
  *pad=qd;
  *padd=qdd;

}

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