Index Page sce2t_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 sce2t_c ( SpiceInt       sc,
                      SpiceDouble    et,
                      SpiceDouble  * sclkdp )

#### Abstract

       Convert ephemeris seconds past J2000 (ET) to integral
       encoded spacecraft clock (`ticks'). For conversion to
       fractional ticks, (required for C-kernel production), see
       the routine sce2c_c..

#### Required_Reading

       SCLK
       TIME

#### Keywords

       CONVERSION
       TIME

#### Brief_I/O

       Variable  I/O  Description
       --------  ---  --------------------------------------------------
       sc         I   NAIF spacecraft ID code.
       et         I   Ephemeris time, seconds past J2000.
       sclkdp     O   SCLK, encoded as ticks since spacecraft clock
                      start.

#### Detailed_Input

       sc             is a NAIF integer code for a spacecraft whose encoded
                      SCLK value at the epoch specified by `et' is desired.

       et             is an epoch, specified as ephemeris seconds past
                      J2000.

#### Detailed_Output

       sclkdp         is an encoded integral spacecraft clock value.
                      `sclkdp' is an encoded representation of the total
                      count of spacecraft clock ticks measured from the
                      time the spacecraft clock started to the epoch `et':
                      partition information IS reflected in the encoded
                      value. `sclkdp' is rounded to the nearest integral
                      double precision number.

#### Parameters

       None.

#### Exceptions

       1)  This function assumes that that an SCLK kernel appropriate
           to the spacecraft clock identified by the input argument sc
           has been loaded.  If an SCLK kernel has not been loaded,
           does not contain all of the required data, or contains
           invalid data, error diagnoses will be performed by functions
           called by this function.  The output argument sclkdp will not
           be modified.

       2)  When using SCLK kernels that map SCLK to a time system other
           than ET (also called barycentric dynamical time---`TDB'), it
           is necessary to have a leapseconds kernel loaded at the time
           this function is called.  If a leapseconds kernel is required
           for conversion between SCLK and ET but is not loaded, the
           error will be diagnosed by functions called by this function.
           The output argument sclkdp will not be modified.

           The time system that an SCLK kernel maps SCLK to is indicated
           by the variable SCLK_TIME_SYSTEM_nn in the kernel, where nn
           is the negative of the NAIF integer code for the spacecraft.
           The time system used in a kernel is TDB if and only if the
           variable is assigned the value 1.

       3)  If the clock type for the spacecraft clock identified by
           `sc' is not supported by this function, the error
           SPICE(NOTSUPPORTED) is signaled.  The output argument `sclkdp'
           will not be modified.

       4)  If the input ET value is not representable as an encoded
           spacecraft clock value for the spacecraft clock identified by
           `sc', the error will be diagnosed by functions called by this
           function.  The output argument sclkdp will not be modified.

#### Files

       None.

#### Particulars

       This function outputs discrete, encoded SCLK values.  Since
       continuous SCLK values are generally more useful, the newer
       function sce2c_c (ET to continuous ticks) should normally be used
       in place of this one.  However, the functionality of this
       routine is needed for converting ET to SCLK strings.

       This function outputs encoded SCLK values.  The advantage of
       encoded SCLK, as opposed to character string representations of
       SCLK, is that encoded SCLK values are easy to perform arithmetic
       operations on.  Also, working with encoded SCLK reduces the
       overhead of repeated conversion of character strings to integers
       or double precision numbers.

       To convert ET to a string representation of an SCLK value, use
       the CSPICE function sce2s_c.

#### Examples

       1)  Convert ET directly to an encoded SCLK value.  Use both of
           these time values to look up both C-kernel (pointing) and
           SPK (position and velocity) data for an epoch specified by an
           ephemeris time.

              During program initialization, load the leapseconds and
              SCLK kernels.  We will pretend that these files are named
              "leapseconds.ker" and "gllsclk.ker".  To use this code
              fragment, you must substitute the actual names of these
              kernel files for the names used here.

                 /.
                 Load leapseconds and SCLK kernels:
                 ./
                 furnsh_c ( "leapseconds.ker" )
                 furnsh_c ( "gllsclk.ker"     )

              The mission is Galileo, which has spacecraft ID -77.
              Let ET be the epoch, specified in ephemeris seconds
              past J2000, at which both position and pointing data
              is desired.

              Find the encoded SCLK value corresponding to ET.

                 sce2t_c  ( -77,  et,  &sclkdp );

              Now you're ready to call both ckgp_c, which expects the input
              epoch to be specified by an encoded SCLK string, and
              spkez_c, which expects the epoch to be specified as an
              ephemeris time.

                 /.
                 Find scan platform pointing cmat and s/c--target
                 vector (first 3 components of state) at epoch.
                 We assume that CK and SPK kernels have been loaded
                 already, via cklpf_c and spklef_c respectively.
                 ./
                 ckgp_c  ( scanpl,  sclkdp,   tol,     refsys,
                           cmat,    &clkout,  &found          );

                 spkez_c ( target,  et,       refsys,  corr,
                           -77,     state,    &lt           );

       2)  Convert UTC to an encoded Voyager 2 SCLK value.

              Again, your initialization code must load the leapseconds
              and SCLK kernels.

                 /.
                 Load leapseconds and SCLK kernels:
                 ./
                 furnsh_c ( "leapseconds.ker" );
                 furnsh_c ( "vgr2sclk.ker"    );

                 /.
                 Find the encoded Voyager 2 SCLK value sclkdp
                 corresponding to the given UTC time.
                 ./
                 utc2et  (  utc,  &et          );
                 sce2t_c ( -32,   et,  &sclkdp );

#### Restrictions

       1)  An SCLK kernel appropriate to the spacecraft clock identified
           by SC must be loaded at the time this function is called.

       2)  If the SCLK kernel used with this function does not map SCLK
           directly to barycentric dynamical time, a leapseconds kernel
           must be loaded at the time this function is called.

#### Literature_References

       [1]  CK Required Reading

       [2]  SPK Required Reading

#### Author_and_Institution

       N.J. Bachman   (JPL)

#### Version

       -CSPICE Version 1.0.2, 27-JAN-2004 (NJB)

          Header was updated to remove comments indicating this routine
          was deprecated.  Minor changes were made to clarify both the
          functionality of this routine and the difference between
          this routine and sce2c_c.  Examples were updated to use furnsh_c.

       -CSPICE Version 1.0.1, 09-MAR-1999 (NJB)

          Updated to reflect the introduction of continuous ticks and
          the function sce2c_c.

          Occurrences of "routine" were changed to "function" in the header.

       -CSPICE Version 1.0.0, 08-FEB-1998 (NJB)

          Based on SPICELIB Version 1.0.2, 10-APR-1992 (NJB) (WLT)

#### Index_Entries

       ephemeris time to spacecraft_clock ticks

#### Link to routine sce2t_c source file sce2t_c.c

    Wed Apr  5 17:54:42 2017