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   et2utc_c ( Ephemeris Time to UTC ) 

   void et2utc_c (  SpiceDouble       et,
                    ConstSpiceChar  * format,
                    SpiceInt          prec,
                    SpiceInt          utclen,
                    SpiceChar       * utcstr   )


   Convert an input time from ephemeris seconds past J2000
   to Calendar, Day-of-Year, or Julian Date format, UTC.






   --------  ---  --------------------------------------------------
   et         I   Input epoch, given in ephemeris seconds past J2000.
   format     I   Format of output epoch.
   prec       I   Digits of precision in fractional seconds or days.
   utclen     I   The length of the output string.
   utcstr     O   Output time string, UTC.


   et          is the input epoch, ephemeris seconds past J2000.

   format      is the format of the output time string. It may be
               any of the following:

                  "C"      Calendar format, UTC.

                  "D"      Day-of-Year format, UTC.

                  "J"      Julian Date format, UTC.

                  "ISOC"   ISO Calendar format, UTC.

                  "ISOD"   ISO Day-of-Year format, UTC.

   prec        is the number of digits of precision to which
               fractional seconds (for Calendar and Day-of-Year
               formats) or days (for Julian Date format) are to
               be computed. If `prec' is zero or smaller, no decimal
               point is appended to the output string. If `prec' is
               greater than 14, it is treated as 14.

   utclen      is the declared length of the output string. This length
               must large enough to hold the output string plus the
               null terminator. If the output string is expected to
               have `x' characters, `utclen' must be x + 1.


   utcstr      is the output time string equivalent to the input
               epoch, in the specified format. Some examples are
               shown below.

                  "C"      "1986 APR 12 16:31:09.814"
                  "D"      "1986-102 // 16:31:12.814"
                  "J"      "JD 2446533.18834276"
                  "ISOC"   "1987-04-12T16:31:12.814"
                  "ISOD"   "1987-102T16:31:12.814"

               If an error occurs, `utcstr' is not changed.

               Fractional seconds, or for Julian dates, fractional
               days, are rounded to the precision level specified
               by the input argument `prec'.

               `utcstr' should be declared to be at least
               20 + prec characters in length to ensure
               sufficient room to hold calendar strings
               for modern epochs. For epochs prior to
               1000 A.D. at least 24 + prec characters in
               length are required to hold the output
               calendar string.

               For epochs prior to 1000 A.D. Jan 1 calendar
               and day of year formats are returned with the
               era (A.D. or B.C.) attached to the year. For

                  "877 A.D. MAR 17 13:29:11.829"
                  "471 B.C. Jan 01 12:00:00.000"
                  "471 B.C. 001 // 12:00:00.000"

               ISO formats do not support the inclusion of an era.
               For years prior to 1 A.D. an error will be signaled
               if ISO format has been requested.




   1)  If the format for the output string is not recognized, the
       error SPICE(INVALIDTIMEFORMAT) is signaled by a routine in the
       call tree of this routine.

   2)  If `prec' is less than or equal to zero, it is treated as
       zero. If `prec' is greater than 14, it is treated as 14.

   3)  If one of the ISO formats is specified (ISOC or ISOD) but the
       year corresponding to `et' is prior to 1 A.D. on the Gregorian
       Calendar, the error SPICE(YEAROUTOFRANGE) is signaled by a
       routine in the call tree of this routine.

   4)  Epochs prior to 15 Oct, 1582 on the Gregorian calendar (the
       calendar commonly used in western societies) are returned in
       the "extended" Gregorian Calendar. To convert epochs to the
       Julian calendar see the SPICELIB routine GR2JUL.

   5)  This routine does not attempt to account for variations
       in the length of the second that were in effect prior
       to Jan 1, 1972. For days prior to that date, we assume
       there are exactly 86400 ephemeris seconds. Consequently
       the UTC Gregorian calendar strings produced for epochs
       prior to Jan 1, 1972 differ from the corresponding
       TDB calendar strings by approximately 41.18 seconds.
       (TDB Gregorian calendar strings are produced by the
       routine etcal_c).

   6)  If a leapseconds kernel has not been loaded prior to calling
       this routine, an error is signaled by a routine in the
       call tree of this routine.

   7)  If the `format' input string pointer is null, the error
       SPICE(NULLPOINTER) is signaled.

   8)  If the `format' input string has zero length, the error
       SPICE(EMPTYSTRING) is signaled.

   9)  If the `utcstr' output string pointer is null, the error
       SPICE(NULLPOINTER) is signaled.

   10) If the `utcstr' output string has length less than two
       characters, the error SPICE(STRINGTOOSHORT) is signaled, since
       the output string is too short to contain one character of
       output data plus a null terminator.


   A leapseconds kernel must be loaded via furnsh_c prior to calling
   this routine. The kernel need be loaded only once during a program


   This routine handles the task of converting a double precision
   representation of an epoch to a character string suitable for
   human consumption. The more general routine timout_c may also be
   used to convert `et' to time strings.


   The numerical results shown for these examples may differ across
   platforms. The results depend on the SPICE kernels used as
   input, the compiler and supporting libraries, and the machine
   specific arithmetic implementation.

   1) Let the value of ET be -527644192.5403653 ephemeris seconds
      past J2000. Assuming that the nominal values in the kernel pool
      have not been altered, the following calls

         et2utc_c ( et, "C", 0, utclen, utcstr );
         et2utc_c ( et, "C", 3, utclen, utcstr );
         et2utc_c ( et, "D", 5, utclen, utcstr );
         et2utc_c ( et, "J", 7, utclen, utcstr );

      produce the following output strings

         1983 APR 13 12:09:14
         1983 APR 13 12:09:14.274
         1983-103 // 12:09:14.27400
         JD 2445438.0064152

      respectively, where utclen is the length of utcstr.

   2) Convert a single ephemeris time to UTC in Julian Date and in
      Calendar formats.

      Use the LSK kernel below to load the leap seconds and time
      constants required for the conversions.


      Example code begins here.

         Program et2utc_ex1
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main()
         Local parameters
         #define TIMLEN          35

         Local variables
         SpiceDouble             et;

         ConstSpiceChar        * format;
         SpiceChar               utcstr[ TIMLEN  ];

         SpiceInt                prec;

         Load the leapseconds kernel.
         furnsh_c ( "naif0012.tls" );

         et     =  -527644192.5403653;
         format = "J";
         prec   =  6;

         et2utc_c (  et , format, prec, TIMLEN, utcstr );

         printf ( "ET:               %18.7f\n"
                  "Converted output: %s\n",
                   utcstr                       );

         return ( 0 );

      When this program was executed on a Mac/Intel/cc/64-bit
      platform, the output was:

      ET:               -527644192.5403653
      Converted output: JD 2445438.006415




   [1]  J. Jespersen and J. Fitz-Randolph, "From Sundials to Atomic
        Clocks, Understanding Time and Frequency," Dover
        Publications, Inc. New York, 1982.


   C.H. Acton          (JPL)
   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)
   W.M. Owen           (JPL)
   B.V. Semenov        (JPL)
   W.L. Taber          (JPL)
   I.M. Underwood      (JPL)
   E.D. Wright         (JPL)


   -CSPICE Version 1.2.0, 24-AUG-2021 (JDR)

       Changed the input argument name "lenout" to "utclen" for consistency
       with other routines.

       Edited the header to comply with NAIF standard.

       Added problem statement and meta-kernel to example #2. Fixed bug
       in example #2.

   -CSPICE Version 1.1.5, 06-APR-2009 (NJB)

       Header was updated to state that fractional
       seconds or days are rounded in the output

   -CSPICE Version 1.1.4, 28-JAN-2008 (BVS)

       Fixed typo in the ISOC example string in -Detailed_Output.

   -CSPICE Version 1.1.3, 16-JAN-2008 (EDW)

       Corrected typos in header titles:

       Detailed Input to -Detailed_Input
       Detailed Output to -Detailed_Output

   -CSPICE Version 1.1.2, 11-JAN-2006 (EDW)

       Added a CHKFSTR check call on the 'format' input string.

   -CSPICE Version 1.1.1, 29-JUL-2003 (NJB) (CHA)

       Various header changes were made to improve clarity and
       more fully explain the routine's functionality.

   -CSPICE Version 1.1.0, 09-FEB-1998 (NJB) (EDW)

       Re-implemented routine without dynamically allocated, temporary
       strings. Added -Exceptions section and corrected typo in chkout_c
       module name.

   -CSPICE Version 1.0.0, 25-OCT-1997 (EDW) (WMO) (IMU) (WLT)


   ephemeris time to utc
Fri Dec 31 18:41:06 2021