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SUBROUTINE slE2H (HA, DEC, PHI, AZ, EL)
*+
* - - - -
* E 2 H
* - - - -
*
* Equatorial to horizon coordinates: HA,Dec to Az,El
*
* (single precision)
*
* Given:
* HA r hour angle
* DEC r declination
* PHI r observatory latitude
*
* Returned:
* AZ r azimuth
* EL r elevation
*
* Notes:
*
* 1) All the arguments are angles in radians.
*
* 2) Azimuth is returned in the range 0-2pi; north is zero,
* and east is +pi/2. Elevation is returned in the range
* +/-pi/2.
*
* 3) The latitude must be geodetic. In critical applications,
* corrections for polar motion should be applied.
*
* 4) In some applications it will be important to specify the
* correct type of hour angle and declination in order to
* produce the required type of azimuth and elevation. In
* particular, it may be important to distinguish between
* elevation as affected by refraction, which would
* require the "observed" HA,Dec, and the elevation
* in vacuo, which would require the "topocentric" HA,Dec.
* If the effects of diurnal aberration can be neglected, the
* "apparent" HA,Dec may be used instead of the topocentric
* HA,Dec.
*
* 5) No range checking of arguments is carried out.
*
* 6) In applications which involve many such calculations, rather
* than calling the present routine it will be more efficient to
* use inline code, having previously computed fixed terms such
* as sine and cosine of latitude, and (for tracking a star)
* sine and cosine of declination.
*
* P.T.Wallace Starlink 9 July 1994
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*
* License:
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program (see SLA_CONDITIONS); if not, write to the
* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301 USA
*
* Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
*-
IMPLICIT NONE
REAL HA,DEC,PHI,AZ,EL
REAL R2PI
PARAMETER (R2PI=6.283185307179586476925286766559)
REAL SH,CH,SD,CD,SP,CP,X,Y,Z,R,A
* Useful trig functions
SH=SIN(HA)
CH=COS(HA)
SD=SIN(DEC)
CD=COS(DEC)
SP=SIN(PHI)
CP=COS(PHI)
* Az,El as x,y,z
X=-CH*CD*SP+SD*CP
Y=-SH*CD
Z=CH*CD*CP+SD*SP
* To spherical
R=SQRT(X*X+Y*Y)
IF (R.EQ.0.0) THEN
A=0.0
ELSE
A=ATAN2(Y,X)
END IF
IF (A.LT.0.0) A=A+R2PI
AZ=A
EL=ATAN2(Z,R)
END
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