Index Page sce2c_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 sce2c_c ( SpiceInt       sc,
                      SpiceDouble    et,
                      SpiceDouble  * sclkdp )

#### Abstract

       Convert ephemeris seconds past J2000 (ET) to continuous encoded
       spacecraft clock (`ticks').  Non-integral tick values may be
       returned.

#### 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.  sclkdp need not be integral.

#### 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 spacecraft clock value.  sclkdp is
                      an encoded representation of the total number
                      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 may be non-integral:  sclkdp is NOT
                      rounded to the nearest whole tick.

#### Parameters

       None.

#### Exceptions

       1)  This routine 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 routines
           called by this routine.  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 routine is called.  If a leapseconds kernel is required
           for conversion between SCLK and ET but is not loaded, the
           error will be diagnosed by routines called by this routine.
           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 routine, the error
           SPICE(NOTSUPPORTED) is signalled.  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 routines called by this
           routine.  The output argument sclkdp will not be modified.

#### Files

       None.

#### Particulars

       This routine outputs continuous encoded SCLK values; unlike the
       routine sce2t_c, the values output by this routine need not be
       integral.

       This routine supports use of non-integral encoded clock values in
       C-kernels:  non-integral clock values may be stored as pointing
       time tags when a C-kernel is created, and they may be supplied
       as request times to the C-kernel readers.

       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 routine sce2s_c.

       See the SCLK Required Reading for a list of the entire set of SCLK
       conversion routines.

#### Examples

       1)  Convert ET directly to a continuous, 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.

                 sce2c_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          );
                 sce2c_c ( -32,   et,  &sclkdp );

#### Restrictions

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

       2)  If the SCLK kernel used with this routine does not map SCLK
           directly to barycentric dynamical time, a leapseconds kernel
           must be loaded at the time this routine 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, 09-NOV-2009   (EDW)

          Corrected typo in header; j2000_c replaced with J2000. Mention of
          the J2000 epoch in the previous header used the word "j2000_c" (wrong)
          instead of "J2000" (correct).

       -CSPICE Version 1.0.1, 14-AUG-2006   (EDW)

          Replace mention of ldpool_c with furnsh_c.

       -CSPICE Version 1.0.0, 18-JUN-1999 (NJB)

#### Index_Entries

       ephemeris time to continuous spacecraft_clock ticks

#### Link to routine sce2c_c source file sce2c_c.c

    Wed Apr  5 17:54:42 2017