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Index Page scdecd_c

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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

       scdecd_c ( Decode spacecraft clock )

       void scdecd_c ( SpiceInt       sc,
                       SpiceDouble    sclkdp,
                       SpiceInt       scllen,
                       SpiceChar    * sclkch  )

#### Abstract

       Convert a double precision encoding of spacecraft clock time into
       a character representation.

#### Required_Reading

       SCLK

#### Keywords

       CONVERSION
       TIME

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       SPICE_SCLK_MXPART
                  P   Maximum number of spacecraft clock partitions.
       sc         I   NAIF spacecraft identification code.
       sclkdp     I   Encoded representation of a spacecraft clock count.
       scllen     I   Maximum allowed length of output SCLK string.
       sclkch     O   Character representation of a clock count.

#### Detailed_Input

       sc          is the NAIF integer code of the spacecraft whose
                   clock's time is being decoded.

       sclkdp      is the double precision encoding of a clock time in
                   units of ticks since the spacecraft clock start time.
                   This value does reflect partition information.

                   An analogy may be drawn between a spacecraft clock
                   and a standard wall clock. The number of ticks
                   corresponding to the wall clock string

                      hh:mm:ss

                   would be the number of seconds represented by that
                   time.

                   For example:

                      Clock string      Number of ticks
                      ------------      ---------------
                        00:00:10              10
                        00:01:00              60
                        00:10:00             600
                        01:00:00            3600

                   If `sclkdp' contains a fractional part the result
                   is the same as if `sclkdp' had been rounded to the
                   nearest whole number.

       scllen      is the maximum number of characters that can be
                   accommodated in the output string. This count
                   includes room for the terminating null character.
                   For example, if the maximum allowed length of the
                   output string, including the terminating null, is 25
                   characters, then `scllen' should be set to 25.

#### Detailed_Output

       sclkch      is the character representation of the clock count.
                   The exact form that `sclkch' takes depends on the
                   spacecraft.

                   Nevertheless, `sclkch' will have the following general
                   format:

                      "pp/sclk_string"

                   "pp" is an integer greater than or equal to one and
                   represents a "partition number".

                   Each mission is divided into some number of partitions.
                   A new partition starts when the spacecraft clock
                   resets, either to zero, or to some other
                   value. Thus, the first partition for any mission
                   starts with launch, and ends with the first clock
                   reset. The second partition starts immediately when
                   the first stopped, and so on.

                   In order to be completely unambiguous about a
                   particular time, you need to specify a partition number
                   along with the standard clock string.

                   Information about when partitions occur for different
                   missions is contained in a spacecraft clock kernel
                   file which needs to be loaded into the kernel pool
                   before calling scdecd_c.

                   The routine scpart_c may be used to read the partition
                   start and stop times, in encoded units of ticks, from
                   the kernel file.

                   Since the end time of one partition is coincident with
                   the begin time of the next, two different time strings
                   with different partition numbers can encode into the
                   same value.

                   For example, if partition 1 ends at time t1, and
                   partition 2 starts at time t2, then

                      "1/t1" and "2/t2"

                   will be encoded into the same value, say X. scdecd_c
                   always decodes such values into the latter of the
                   two partitions. In this example,

                     scdecd_c ( x, sc, scllen, clkstr )

                   will result in

                      clkstr = "2/t2".

                   "sclk_string" is a spacecraft specific clock string,
                   typically consisting of a number of components
                   separated by delimiters.

                   Using Galileo as an example, the full format is

                      wwwwwwww:xx:y:z

                   where z is a mod-8 counter (values 0-7) which
                   increments approximately once every 8 1/3 ms., y is a
                   mod-10 counter (values 0-9) which increments once
                   every time z turns over, i.e., approximately once every
                   66 2/3 ms., xx is a mod-91 (values 0-90) counter
                   which increments once every time y turns over, i.e.,
                   once every 2/3 seconds. wwwwwwww is the Real-Time Image
                   Count (RIM), which increments once every time xx turns
                   over, i.e., once every 60 2/3 seconds. The roll-over
                   expression for the RIM is 16777215, which corresponds
                   to approximately 32 years.

                   wwwwwwww, xx, y, and z are referred to interchangeably
                   as the fields or components of the spacecraft clock.
                   SCLK components may be separated by any of these five
                   characters: " "  ":"  ","  "-"  "."
                   The delimiter used is determined by a kernel pool
                   variable and can be adjusted by the user.

                   Some spacecraft clock components have offset, or
                   starting, values different from zero. For example,
                   with an offset value of 1, a mod 20 counter would
                   cycle from 1 to 20 instead of from 0 to 19.

                   See the SCLK required reading for a detailed
                   description of the Voyager and Mars Observer clock
                   formats.

#### Parameters

       SPICE_SCLK_MXPART

                   is the maximum number of spacecraft clock partitions
                   expected in the kernel file for any one spacecraft.
                   See the header file SpiceSCLK.h for this parameter's
                   value.

#### Exceptions

       1)  If kernel variables required by this routine are unavailable,
           an error is signaled by a routine in the call tree of this
           routine. `sclkch' will be returned as a blank string in this
           case.

       2)  If the number of partitions in the kernel file for spacecraft `sc'
           exceeds the parameter SPICE_SCLK_MXPART, the error
           SPICE(TOOMANYPARTS) is signaled by a routine in the call tree of this
           routine. `sclkch' will be returned as a blank string in this case.

       3)  If the encoded value does not fall in the boundaries of the
           mission, the error SPICE(VALUEOUTOFRANGE) is signaled by a
           routine in the call tree of this routine. `sclkch' will be
           returned as a blank string in this case.

       4)  If the declared length of `sclkch' is not large enough to
           contain the output clock string, the error
           SPICE(SCLKTRUNCATED) is signaled by either this routine or a
           routine in the call tree of this routine. On output `sclkch'
           will contain a portion of the truncated clock string.

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

       6)  If the `sclkch' 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.

#### Files

       A kernel file containing spacecraft clock partition information
       for the desired spacecraft must be loaded, using the routine
       furnsh_c, before calling this routine.

#### Particulars

       In general, it is difficult to compare spacecraft clock counts
       numerically since there are too many clock components for a
       single comparison. The routine scencd_c provides a method of
       assigning a single double precision number to a spacecraft's
       clock count, given one of its character representations.

       This routine performs the inverse operation to scencd_c, converting
       an encoded double precision number to character format.

       To convert the number of ticks since the start of the mission to
       a clock format character string, scdecd_c:

          1) Determines the spacecraft clock partition that TICKS falls
             in.

          2) Subtracts off the number of ticks occurring in previous
             partitions, to get the number of ticks since the beginning
             of the current partition.

          3) Converts the resulting ticks to clock format and forms the
             string

                "partition_number/clock_string"

#### Examples

       The numerical results shown for this example 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) Double precision encodings of spacecraft clock counts are used
          to tag pointing data in the C-kernel.

          In the following example, pointing for a sequence of images
          from the CASSINI Imaging Science Subsystem (ISS) is requested
          from the C-kernel using an array of character spacecraft clock
          counts as input. The clock counts attached to the output are
          then decoded to character and compared with the input strings.

          Use the CK kernel below to load the CASSINI image navigated
          spacecraft pointing and orientation data.

             04153_04182ca_ISS.bc

          Use the SCLK kernel below to load the CASSINI spacecraft clock
          time correlation data required for the conversion between
          spacecraft clock string representation and double precision
          encoding of spacecraft clock counts.

             cas00071.tsc

          Example code begins here.

          /.
             Program scdecd_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main()
          {
             /.
             Local parameters.

             The instrument we want pointing for is the CASSINI
             spacecraft. The reference frame we want is
             J2000. The spacecraft is CASSINI.
             ./
             #define  SC         -82
             #define  INST       -82000
             #define  REF        "J2000"
             #define  CK         "04153_04182ca_ISS.bc"
             #define  SCLK       "cas00071.tsc"
             #define  NPICS      4
             #define  CLKTOL     "1.0"
             #define  MAXLEN     30

             /.
             Local variables.
             ./
             SpiceBoolean       found;

             SpiceChar          sclkout[25];

             SpiceDouble        tol;
             SpiceDouble        timein;
             SpiceDouble        timeout;
             SpiceDouble        cmat   [3][3];

             SpiceInt           i;

             /.
             Set the input SCLK strings.
             ./
             SpiceChar          sclkin [4][25] = { {"1/1465644279.0"},
                                                   {"1/1465644281.0"},
                                                   {"1/1465644351.0"},
                                                   {"1/1465644361.0"} };

             /.
             Load the appropriate files. We need

                1. CK file containing pointing data.
                2. Spacecraft clock kernel file.
             ./
             furnsh_c ( CK   );
             furnsh_c ( SCLK );

             /.
             Convert the tolerance string to ticks.
             ./
             sctiks_c ( SC, CLKTOL, &tol );

             for ( i = 0;  i < NPICS;  i++ )
             {
                scencd_c ( SC,   sclkin[i], &timein );

                ckgp_c   ( INST,  timein,    tol,    REF,
                           cmat,  &timeout,  &found       );

                printf ( "\nInput s/c clock count : %s\n", sclkin[i] );
                if ( found )
                {
                   scdecd_c ( SC, timeout, MAXLEN, sclkout );

                   printf ( "Output s/c clock count: %s\n"
                            "Output C-Matrix:\n"
                            "   %19.15f   %19.15f   %19.15f\n"
                            "   %19.15f   %19.15f   %19.15f\n"
                            "   %19.15f   %19.15f   %19.15f\n",
                            sclkout,
                            cmat[0][0],  cmat[0][1],  cmat[0][2],
                            cmat[1][0],  cmat[1][1],  cmat[1][2],
                            cmat[2][0],  cmat[2][1],  cmat[2][2] );
                }
                else
                {
                   printf ( "No pointing found.\n" );
                }
             }

             return ( 0 );
          }

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

          Input s/c clock count : 1/1465644279.0
          No pointing found.

          Input s/c clock count : 1/1465644281.0
          Output s/c clock count: 1/1465644281.171
          Output C-Matrix:
              -0.335351455948710     0.864374440205611     0.374694846658341
              -0.937887426812980    -0.343851965210223    -0.046184419961653
               0.088918927227039    -0.366909598048763     0.925997176691424

          Input s/c clock count : 1/1465644351.0
          Output s/c clock count: 1/1465644351.071
          Output C-Matrix:
              -0.335380929397586     0.864363638262230     0.374693385378623
              -0.937874292008090    -0.343889838107825    -0.046169163264003
               0.088946301703530    -0.366899550417080     0.925998528787713

          Input s/c clock count : 1/1465644361.0
          No pointing found.

#### Restrictions

       1)  Assumes that an SCLK kernel file appropriate for the clock
           designated by `sc' is loaded in the kernel pool at the time
           this routine is called.

#### Literature_References

       None.

#### Author_and_Institution

       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       E.D. Wright         (JPL)

#### Version

       -CSPICE Version 1.3.0, 05-AUG-2021 (JDR)

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

           Edited the header to comply with NAIF standard. Reformatted
           example's output and updated kernel set to work with PDS
           archived CASSINI data.

       -CSPICE Version 1.2.0, 11-FEB-2008 (NJB)

           Definition of constant macro MXPART was deleted.
           Documentation was updated to reflect current
           MXPART value of 9999.

       -CSPICE Version 1.1.2, 14-AUG-2006 (EDW)

           Replace mention of ldpool_c with furnsh_c.

       -CSPICE Version 1.1.1, 26-MAR-2003 (NJB)

           Fixed description of exception (6):  replaced "scllen-1"
           with "scllen." Corrected spelling of "signaled."

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

           Re-implemented routine without dynamically allocated, temporary
           strings. Added output string length and pointer checks.

       -CSPICE Version 1.0.0, 25-OCT-1997 (NJB)

#### Index_Entries

       decode spacecraft_clock

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

    Fri Dec 31 18:41:11 2021