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era.pvtob.md

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eraPvtob

pv = ERFA.pvtob(elong, phi, hm, xp, yp, sp, theta)

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) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.