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SUBROUTINE slH2E ( AZ, EL, PHI, HA, DEC )
*+
* - - - - -
* D E 2 H
* - - - - -
*
* Horizon to equatorial coordinates: Az,El to HA,Dec
*
* (single precision)
*
* Given:
* AZ r azimuth
* EL r elevation
* PHI r observatory latitude
*
* Returned:
* HA r hour angle
* DEC r declination
*
* Notes:
*
* 1) All the arguments are angles in radians.
*
* 2) The sign convention for azimuth is north zero, east +pi/2.
*
* 3) HA is returned in the range +/-pi. Declination is returned
* in the range +/-pi/2.
*
* 4) The latitude is (in principle) geodetic. In critical
* applications, corrections for polar motion should be applied.
*
* 5) In some applications it will be important to specify the
* correct type of elevation in order to produce the required
* type of HA,Dec. In particular, it may be important to
* distinguish between the elevation as affected by refraction,
* which will yield the "observed" HA,Dec, and the elevation
* in vacuo, which will yield the "topocentric" HA,Dec. If the
* effects of diurnal aberration can be neglected, the
* topocentric HA,Dec may be used as an approximation to the
* "apparent" HA,Dec.
*
* 6) No range checking of arguments is done.
*
* 7) 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.
*
* Last revision: 11 September 2005
*
* Copyright P.T.Wallace. All rights reserved.
*
* 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 AZ, EL, PHI, HA, DEC
DOUBLE PRECISION SA, CA, SE, CE, SP, CP, X, Y, Z, R
* Useful trig functions.
SA = SIN(AZ)
CA = COS(AZ)
SE = SIN(EL)
CE = COS(EL)
SP = SIN(PHI)
CP = COS(PHI)
* HA,Dec as x,y,z.
X = -CA*CE*SP+SE*CP
Y = -SA*CE
Z = CA*CE*CP+SE*SP
* To HA,Dec.
R = SQRT(X*X+Y*Y)
IF (R.EQ.0.0) THEN
HA = 0.0
ELSE
HA = REAL(ATAN2(Y,X))
END IF
DEC = REAL(ATAN2(Z,R))
END
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