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# pvtob

erfa.pvtob(elong, phi, hm, xp, yp, sp, theta)

  Position and velocity of a terrestrial observing station.

  Parameters:
    elong double array
    phi double array
    hm double array
    xp double array
    yp double array
    sp double array
    theta double array
  Returns:
    pv double array

  Notes

  Wraps ERFA function `eraPvtob`. The ERFA documentation is:

      - - - - - - - - -
       e r a P v t o b
      - - - - - - - - -

      Position and velocity of a terrestrial observing station.

      Given:
         elong   double       longitude (radians, east +ve, Note 1)
         phi     double       latitude (geodetic, radians, Note 1)
         hm      double       height above ref. ellipsoid (geodetic, m)
         xp,yp   double       coordinates of the pole (radians, Note 2)
         sp      double       the TIO locator s' (radians, Note 2)
         theta   double       Earth rotation angle (radians, Note 3)

      Returned:
         pv      double[2][3] position/velocity vector (m, m/s, CIRS)

      Notes:

      1) The terrestrial coordinates are with respect to the ERFA_WGS84
         reference ellipsoid.

      2) xp and yp are the coordinates (in radians) of the Celestial
         Intermediate Pole with respect to the International Terrestrial
         Reference System (see IERS Conventions), measured along the
         meridians 0 and 90 deg west respectively.  sp is the TIO locator
         s', in radians, which positions the Terrestrial Intermediate
         Origin on the equator.  For many applications, xp, yp and
         (especially) sp can be set to zero.

      3) If theta is Greenwich apparent sidereal time instead of Earth
         rotation angle, the result is with respect to the true equator
         and equinox of date, i.e. with the x-axis at the equinox rather
         than the celestial intermediate origin.

      4) The velocity units are meters per UT1 second, not per SI second.
         This is unlikely to have any practical consequences in the modern
         era.

      5) No validation is performed on the arguments.  Error cases that
         could lead to arithmetic exceptions are trapped by the eraGd2gc
         function, and the result set to zeros.

      References:

         McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
         IERS Technical Note No. 32, BKG (2004)

         Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to
         the Astronomical Almanac, 3rd ed., University Science Books
         (2013), Section 7.4.3.3.

      Called:
         eraGd2gc     geodetic to geocentric transformation
         eraPom00     polar motion matrix
         eraTrxp      product of transpose of r-matrix and p-vector

      This revision:   2021 February 24

      Copyright (C) 2013-2023, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.