Updates for SOFA Release 18 : 2021 May 11
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Summary of Changes
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The changes fall into the following categories:

(1) Introduction of three new support routines.  Two deal with 
    calculating astrometric places, while the third provides the 
    approximate lunar position and velocity.  The validation program 
    has been duly updated.

(2) A rearrangement of the ANSI C header files sofam.h and sofa.h. 
    The consequence of this is that an explicit #include "sofam.h" 
    has been added to many of the SOFA functions.  Thus developers 
    of applications that use constants from sofa.h will now need to 
    include an explicit #include <sofam.h>.  Further explanation is 
    given below.
    
(3) The year of validity for the leap second (dat) routine has been 
    extended.

(4) Typographical and other minor corrections to the documentation. 
    Those that are purely typographical (e.g. punctuation) are not 
    listed).

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FORTRAN 77 Library
------------------

iau_ATCC13  New support routine to transform a star's ICRS catalog 
            entry (epoch J2000.0) into ICRS astrometric place.
            
iau_ATCCQ   New support routine; a "quick" transformation of a star's 
            ICRS catalog entry (epoch J2000.0) into ICRS astrometric 
            place, given precomputed star-independent astrometry 
            parameters.

iau_dat     Year extended to 2021.

iau_G2ICRS  Documentation updated.
iau_ICRS2G

iau_MOON98  New support routine for calculating approximate geocentric 
            position and velocity of the Moon.  
 
iau_PLAN94  Documentation updates and corrections.
 
t_sofa_f    The test program has been updated to include the three new 
            routines.

N.B. Both iau_MOON98 and iau_PLAN94 provide only approximate positions
     and do not use IAU endorsed theories.

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ANSI C Library
--------------

sofa.h      The information in both these files has been rearranged to
sofam.h     eliminate problems encountered by C++ developers.  
            The change has 
            (i)  moved the structures from sofam.h into sofa.h and
            (ii) thus eliminated the #include "sofam.h" from sofa.h.
            The consequence of this change for SOFA functions is that 
            an explicit #include "sofam.h" has had to be added to some 
            of them.

            Previously, sofam.h contained both structure definitions and
            constants, and was #included by sofa.h, which was otherwise
            dedicated to function prototypes.  The difficulty was that 
            short uppercase names in sofam.h were colliding with 
            C++ variables. 

            The consequence of the change for developers is that any 
            application that uses constants from sofa.h will now need an 
            explicit #include <sofam.h>.  It should, however, be noted 
            that the contents of sofam.h are not formally part of the 
            SOFA API, and so such an application is vulnerable to 
            future changes.  Rather than adding an #include <sofam.h> 
            to applications, it would be better to replicate the needed 
            macros in the user code.

iauAtcc13   New support function to transform a star's ICRS catalog 
            entry (epoch J2000.0) into ICRS astrometric place.

iauAtccq    New support function, a "quick" transformation of a star's
            ICRS catalog entry (epoch J2000.0) into ICRS astrometric 
            place, given precomputed star-independent astrometry 
            parameters.

iauDat      Year extended to 2021.

iauG2icrs   Documentation updated.
iauIcrs2g

makefile    An error has been corrected when using "make check".  The 
            directory for the include files was incorrect.

iauMoon98   New support function for calculating approximate geocentric 
            position and velocity of the Moon.  

iauPlan94   Documentation updates and corrections.

t_sofa_c    The test program has been updated to include the three new 
            functions.

Cosmetic changes to improve consistency have been made to the ANSI C code.

N.B. Both iauMoon98 and iauPlan94 provide only approximate positions 
     and do not use IAU endorsed theories.

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+ SOFA thanks all those who have reported the various issues that go
+ to ensuring the libraries and documentation are kept up-to-date and
+ relevant.
+
+ End of updates
+ 2021 May 11
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