Next: SLA_DEULER  Euler Angles to Rotation Matrix
Up: SUBPROGRAM SPECIFICATIONS
Previous: SLA_DD2TF  Days to Hour,Min,Sec
SLA_DE2H  to Az,El
 ACTION:
 Equatorial to horizon coordinates
(double precision).
 CALL:
 CALL sla_DE2H (HA, DEC, PHI, AZ, EL)
 GIVEN:

HA 
D 
hour angle (radians) 
DEC 
D 
declination (radians) 
PHI 
D 
latitude (radians) 
 RETURNED:

AZ 
D 
azimuth (radians) 
EL 
D 
elevation (radians) 
 NOTES:
 1.
 Azimuth is returned in the range ; north is zero,
and east is . Elevation is returned in the range
.
 2.
 The latitude must be geodetic. In critical applications,
corrections for polar motion should be applied.
 3.
 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 , and the elevation
in vacuo, which would require the topocentric
. If the effects of diurnal aberration can be neglected, the
apparent may be used instead of the topocentric
.
 4.
 No range checking of arguments is carried out.
 5.
 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.
Next: SLA_DEULER  Euler Angles to Rotation Matrix
Up: SUBPROGRAM SPECIFICATIONS
Previous: SLA_DD2TF  Days to Hour,Min,Sec
SLALIB  Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
Email:ptw@star.rl.ac.uk