SLA_DH2E - Az,El to $h,\delta$

ACTION:

Horizon to equatorial coordinates (double precision).

CALL:

CALL sla_DH2E (AZ, EL, PHI, HA, DEC)

GIVEN:

AZ azimuth (radians)

EL D elevation (radians)

PHI D latitude (radians)

RETURNED:

HA hour angle (radians)

DEC D declination (radians)

NOTES:

1.

The sign convention for azimuth is north zero, east $+\pi/2$.

2.

HA is returned in the range $\pm \pi$. Declination is returned in the range $\pm \pi$.

3.

The latitude is (in principle) geodetic. In critical applications, corrections for polar motion should be applied (see sla_POLMO).

4.

In some applications it will be important to specify the correct type of elevation in order to produce the required type of $[\,h,\delta\,]$. In particular, it may be important to distinguish between the elevation as affected by refraction, which will yield the observed $[\,h,\delta\,]$, and the elevation in vacuo, which will yield the topocentric $[\,h,\delta\,]$. If the effects of diurnal aberration can be neglected, the topocentric $[\,h,\delta\,]$ may be used as an approximation to the apparent $[\,h,\delta\,]$.

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.