[

define_tag:'lp_math_earthRotationAngle',
	-description='Returns the earth rotation angle in radians given a Julian date.',
	-priority='replace',
	-required='JulianDate';

	// adapted from i a u _ E R A 0 0
	// original Fortran version follows below

	local:'DJ' = (lp_date_juliansplit: #juliandate);
	local:'DJ1' = (decimal: #DJ->(find:'date'));
	local:'DJ2' = (decimal: #DJ->(find:'time'));

	// *  Days since fundamental epoch.
	if: #DJ1 < #DJ2;
		local:'D1' = @#DJ1;
		local:'D2' = @#DJ2;
	else;
		local:'D1' = @#DJ2;
		local:'D2' = @#DJ1;	
	/if;
	
    local:'T' = #D1 + ( #D2-2451545.0 );

	// *  Fractional part of T (days).
    local:'F' = lp_math_mod( #D1, 1.0 ) + lp_math_mod ( #D2, 1.0 );

	// *  Earth rotation angle at this UT1.
    return: lp_decimal_precisionset(lp_math_range2PI( 6.283185307179586476925287 * ( #F + 0.7790572732640
                                       + 0.00273781191135448 * #T ) ));

/define_tag;


/*

      DOUBLE PRECISION FUNCTION iau_ERA00 ( DJ1, DJ2 )
*+
*  - - - - - - - - - -
*   i a u _ E R A 0 0
*  - - - - - - - - - -
*
*  Earth rotation angle (IAU 2000 model).
*
*  This routine is part of the International Astronomical Union's
*  SOFA (Standards of Fundamental Astronomy) software collection.
*
*  Status:  canonical model.
*
*  Given:
*     DJ1,DJ2     d      UT1 as a 2-part Julian Date (see note)
*
*  The result is the Earth Rotation Angle (radians), in the range 0 to
*  2pi.
*
*  Notes:
*
*  1) The UT1 date DJ1+DJ2 is a Julian Date, apportioned in any
*     convenient way between the arguments DJ1 and DJ2.  For example,
*     JD(UT1)=2450123.7 could be expressed in any of these ways,
*     among others:
*
*             DJ1            DJ2
*
*         2450123.7D0        0D0        (JD method)
*          2451545D0      -1421.3D0     (J2000 method)
*         2400000.5D0     50123.2D0     (MJD method)
*         2450123.5D0       0.2D0       (date & time method)
*
*     The JD method is the most natural and convenient to use in
*     cases where the loss of several decimal digits of resolution
*     is acceptable.  The J2000 and MJD methods are good compromises
*     between resolution and convenience.  The date & time method is
*     best matched to the algorithm used:  maximum accuracy (or, at
*     least, minimum noise) is delivered when the DJ1 argument is for
*     0hrs UT1 on the day in question and the DJ2 argument lies in the
*     range 0 to 1, or vice versa.
*
*  2) The algorithm is adapted from Expression 22 of Capitaine et al
*     2000.  The time argument has been expressed in days directly,
*     and, to retain precision, integer contributions have been
*     eliminated.  A similar formulation is given on p35 of the IERS
*     Conventions (1996).
*
*  Called:
*     iau_ANP        normalize angle into range 0 to 2pi
*
*  References:
*
*     Capitaine N., Guinot B. and McCarthy D.D, 2000, A&A 355,
*     398-405.
*
*     McCarthy D.D., 1996, IERS Conventions (IERS Technical Note 21),
*     Observatoire de Paris.
*
*  This revision:  2004 February 27
*
*  Copyright (C) 2005 IAU SOFA Review Board.  See notes at end.
*
*-----------------------------------------------------------------------

      IMPLICIT NONE

      DOUBLE PRECISION DJ1, DJ2

*  2Pi
      DOUBLE PRECISION D2PI
      PARAMETER ( D2PI = 6.283185307179586476925287D0 )

*  Reference epoch (J2000), JD
      DOUBLE PRECISION DJ0
      PARAMETER ( DJ0 = 2451545D0 )

      DOUBLE PRECISION D1, D2, T, F

      DOUBLE PRECISION iau_ANP

* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

*  Days since fundamental epoch.
      IF ( DJ1 .LT. DJ2 ) THEN
         D1 = DJ1
         D2 = DJ2
      ELSE
         D1 = DJ2
         D2 = DJ1
      END IF
      T = D1 + ( D2-DJ0 )

*  Fractional part of T (days).
      F = MOD ( D1, 1D0 ) + MOD ( D2, 1D0 )

*  Earth rotation angle at this UT1.
      iau_ERA00 = iau_ANP ( D2PI * ( F + 0.7790572732640D0
     :                                 + 0.00273781191135448D0 * T ) )

*  Finished.

*+----------------------------------------------------------------------
*
*  Copyright (C) 2005
*  Standards Of Fundamental Astronomy Review Board
*  of the International Astronomical Union.
*
*  =====================
*  SOFA Software License
*  =====================
*
*  NOTICE TO USER:
*
*  BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING TERMS AND CONDITIONS
*  WHICH APPLY TO ITS USE.
*
*  1. The Software is owned by the IAU SOFA Review Board ("the Board").
*
*  2. The Software is made available free of charge for use by:
*
*     a) private individuals for non-profit research; and
*
*     b) non-profit educational, academic and research institutions.
*
*  3. Commercial use of the Software is specifically excluded from the
*     terms and conditions of this license.  Commercial use of the
*     Software is subject to the prior written agreement of the Board on
*     terms to be agreed.
*
*  4. The provision of any version of the Software under the terms and
*     conditions specified herein does not imply that future versions
*     will also be made available under the same terms and conditions.
*
*  5. The user may modify the Software for his/her own purposes.  The
*     user may distribute the modified software provided that the Board
*     is informed and that a copy of the modified software is made
*     available to the Board on request.  All modifications made by the
*     user shall be clearly identified to show how the modified software
*     differs from the original Software, and the name(s) of the
*     affected routine(s) shall be changed.  The original SOFA Software
*     License text must be present.
*
*  6. In any published work produced by the user and which includes
*     results achieved by using the Software, the user shall acknowledge
*     that the Software was used in producing the information contained
*     in such publication.
*
*  7. The user may incorporate or embed the Software into other software
*     products which he/she may then give away free of charge but not
*     sell provided the user makes due acknowledgement of the use which
*     he/she has made of the Software in creating such software
*     products.  Any redistribution of the Software in this way shall be
*     made under the same terms and conditions under which the user
*     received it from the SOFA Center.
*
*  8. The user shall not cause the Software to be brought into
*     disrepute, either by misuse, or use for inappropriate tasks, or by
*     inappropriate modification.
*
*  9. The Software is provided to the user "as is" and the Board makes
*     no warranty as to its use or performance.   The Board does not and
*     cannot warrant the performance or results which the user may
*     obtain by using the Software.  The Board makes no warranties,
*     express or implied, as to non-infringement of third party rights,
*     merchantability, or fitness for any particular purpose.  In no
*     event will the Board be liable to the user for any consequential,
*     incidental, or special damages, including any lost profits or lost
*     savings, even if a Board representative has been advised of such
*     damages, or for any claim by any third party.
*
*  Correspondence concerning SOFA software should be addressed as
*  follows:
*
*     Internet email: sofa@rl.ac.uk
*     Postal address: IAU SOFA Center
*                     Rutherford Appleton Laboratory
*                     Chilton, Didcot, Oxon OX11 0QX
*                     United Kingdom
*
*
*-----------------------------------------------------------------------

      END


*/

]