deltet_c

Index Page deltet_c
A B C D E F G H I J K L M N O P Q R S T U V W X
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       void deltet_c ( SpiceDouble      epoch,
                       ConstSpiceChar * eptype,
                       SpiceDouble    * delta )
#### Abstract
       Return the value of Delta ET (ET-UTC) for an input epoch.
#### Required_Reading
       TIME
       KERNEL
#### Keywords
       TIME
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       epoch      I   Input epoch (seconds past J2000).
       eptype     I   Type of input epoch ("UTC" or "ET").
       delta      O   Delta ET (ET-UTC) at input epoch.
#### Detailed_Input
       epoch       is the epoch at which "delta ET" is to be computed.
                   `epoch' may be either UTC or ephemeris seconds past
                   J2000, as specified by EPTYPE.

       eptype      indicates the type of input epoch. It may be either
                   of the following:

                      "UTC"    UTC seconds past J2000 UTC.

                      "ET"     Ephemeris seconds past J2000 TDB,
                               also known as barycentric dynamical
                               time (TDB).
#### Detailed_Output
       delta       is the value of

                      "delta ET" = ET - UTC

                   at the input epoch. This is added to UTC to give
                   ET, or subtracted from ET to give UTC. The routine
                   is reversible: that is, given the following calls,

                      deltet_c ( utc,      "UTC", &del1 );
                      deltet_c ( utc+del1, "ET",  &del2 );

                   the expression

                      ( del1 == del2 )

                   is true.
#### Parameters
       None.
#### Exceptions
       1) If the input epoch is not recognized, the error
          SPICE(INVALIDEPOCH) is signaled.

       2) If the variables necessary for the computation of delta
          have not been loaded into the kernel pool, the error
          SPICE(KERNELVARNOTFOUND) is signaled.

       3) If the number of leapseconds in the pool is greater than
          the local leapseconds buffer size, the error
          SPICE(BUFFEROVERFLOW) is signaled.

       4) The error SPICE(EMPTYSTRING) is signaled if the input
          string `eptype' does not contain at least one character, since
          the input string cannot be converted to a Fortran-style string in
          this case.

       5) The error SPICE(NULLPOINTER) is signaled if the input string
          pointer is null.
#### Files
       None.
#### Particulars
       The value of Delta ET is given by

          delta = ( ET - TAI ) + leap seconds

       where TAI is the atomic time corresponding to the input epoch.
#### Examples
       The following example shows how deltet_c may be used to convert
       from UTC seconds past J2000 to TDB seconds past J2000.

          deltet_c ( utcsec, "UTC", &delta );
          et = utcsec + delta

       The following example shows how deltet_c may be used to convert
       from ephemeris seconds past J2000 to UTC seconds past J2000.

          deltet_c ( et, "et", &delta );
          utcsec = et - delta;

       See the TIME Required Reading for further examples.
#### Restrictions
       The routines str2et_c and timout_c are preferred for conversions
       between UTC string and ET represented as seconds past J2000 TDB.

       This routine is provided mainly to provide a method of representing
       an epoch as UTC seconds past J2000.
#### Literature_References
       [1] Astronomical Almanac.
#### Author_and_Institution
       N.J. Bachman    (JPL)
       W.M. Owen       (JPL)
       I.M. Underwood  (JPL)
#### Version
       -CSPICE Version 1.0.0, 01-AUG-2003 (NJB) (WMO) (IMU)
#### Index_Entries
       difference between ephemeris time and utc
#### Link to routine deltet_c source file deltet_c.c

    Thu Apr 16 08:57:43 2009