.help altaz Jun99 "Slalib Package"
.nf

      SUBROUTINE slALAZ (HA, DEC, PHI,
     :                      AZ, AZD, AZDD, EL, ELD, ELDD, PA, PAD, PADD)

     - - - - - -
      A L A Z
     - - - - - -

  Positions, velocities and accelerations for an altazimuth
  telescope mount.

  (double precision)

  Given:
     HA      d     hour angle
     DEC     d     declination
     PHI     d     observatory latitude

  Returned:
     AZ      d     azimuth
     AZD     d        "    velocity
     AZDD    d        "    acceleration
     EL      d     elevation
     ELD     d         "     velocity
     ELDD    d         "     acceleration
     PA      d     parallactic angle
     PAD     d         "      "   velocity
     PADD    d         "      "   acceleration

  Notes:

  1)  Natural units are used throughout.  HA, DEC, PHI, AZ, EL
      and ZD are in radians.  The velocities and accelerations
      assume constant declination and constant rate of change of
      hour angle (as for tracking a star);  the units of AZD, ELD
      and PAD are radians per radian of HA, while the units of AZDD,
      ELDD and PADD are radians per radian of HA squared.  To
      convert into practical degree- and second-based units:

        angles * 360/2pi -> degrees
        velocities * (2pi/86400)*(360/2pi) -> degree/sec
        accelerations * ((2pi/86400)**2)*(360/2pi) -> degree/sec/sec

      Note that the seconds here are sidereal rather than SI.  One
      sidereal second is about 0.99727 SI seconds.

      The velocity and acceleration factors assume the sidereal
      tracking case.  Their respective numerical values are (exactly)
      1/240 and (approximately) 1/3300236.9.

  2)  Azimuth is returned in the range 0-2pi;  north is zero,
      and east is +pi/2.  Elevation and parallactic angle are
      returned in the range +/-pi/2.  Position angle is +ve
      for a star west of the meridian and is the angle NP-star-zenith.

  3)  The latitude is geodetic as opposed to geocentric.  The
      hour angle and declination are topocentric.  Refraction and
      deficiencies in the telescope mounting are ignored.  The
      purpose of the routine is to give the general form of the
      quantities.  The details of a real telescope could profoundly
      change the results, especially close to the zenith.

  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.

  P.T.Wallace   Starlink   14 March 1997

  Copyright (C) 1997 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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