SLA_DE2H - $h,\delta$ to Az,El

ACTION:

Equatorial to horizon coordinates (double precision).

CALL:

CALL sla_DE2H (HA, DEC, PHI, AZ, EL)

GIVEN:

HA hour angle (radians)

DEC D declination (radians)

PHI D latitude (radians)

RETURNED:

AZ azimuth (radians)

EL D elevation (radians)

NOTES:

1.

Azimuth is returned in the range $0\!-\!2\pi$; north is zero, and east is $+\pi/2$. Elevation is returned in the range $\pm \pi$.

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 $[\,h,\delta\,]$, and the elevation in vacuo, which would require the topocentric $[\,h,\delta\,]$. If the effects of diurnal aberration can be neglected, the apparent $[\,h,\delta\,]$ may be used instead of the topocentric $[\,h,\delta\,]$.

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.