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.help dh2e Jun99 "Slalib Package"
.nf
SUBROUTINE slDH2E (AZ, EL, PHI, HA, DEC)
- - - - -
D E 2 H
- - - - -
Horizon to equatorial coordinates: Az,El to HA,Dec
(double precision)
Given:
AZ d azimuth
EL d elevation
PHI d observatory latitude
Returned:
HA d hour angle
DEC d 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.
P.T.Wallace Starlink 21 February 1996
Copyright (C) 1996 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
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