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.help e2h Jun99 "Slalib Package"
.nf
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
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
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