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scencd

Table of contents
Procedure
Abstract
Required_Reading
Keywords
Declarations
Brief_I/O
Detailed_Input
Detailed_Output
Parameters
Exceptions
Files
Particulars
Examples
Restrictions
Literature_References
Author_and_Institution
Version

Procedure

     SCENCD ( Encode spacecraft clock )

     SUBROUTINE SCENCD ( SC, SCLKCH, SCLKDP )

Abstract

     Encode a character representation of spacecraft clock time into a
     double precision number.

Required_Reading

     SCLK

Keywords

     CONVERSION
     TIME

Declarations

     IMPLICIT NONE

     INCLUDE               'sclk.inc'

     INTEGER               SC
     CHARACTER*(*)         SCLKCH
     DOUBLE PRECISION      SCLKDP

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     SC         I   NAIF spacecraft identification code.
     SCLKCH     I   Character representation of a spacecraft clock.
     SCLKDP     O   Encoded representation of the clock count.
     MXPART     P   Maximum number of spacecraft clock partitions.

Detailed_Input

     SC       is the standard NAIF ID of the spacecraft whose clock's
              time is being encoded.

     SCLKCH   is the character representation of some spacecraft's
              clock count.

              SCLKCH will have the following general format:

                 'pp/sclk_string', or just
                    'sclk_string'

              'pp' is an integer greater than or equal to one
              and is called the 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,
              using the routine FURNSH.

              The routine SCPART is used to read the partition
              start and stop times, in encoded units of SCLK (called
              "ticks" -- see SCLKDP below) from the kernel file.

              If the partition number is included, it must be
              separated from the rest of the string by a '/'.
              Any number of spaces may separate the partition number,
              the '/', and the rest of the clock string.

              If the partition number is omitted, a default partition
              will be assumed. The default partition is the lowest-
              numbered partition that contains the given clock time.
              If the clock time does not fall in any of the
              partition boundaries then an error is signaled.

              'sclk_string' is a spacecraft specific clock string.
              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: ' '  ':'  ','  '-'  '.'
              Any number of spaces can separate the components and
              the delimiters. The presence of the RIM component
              is required. Successive components may be omitted, and
              in such cases are assumed to represent zero values.

              Values for the individual components may exceed the
              maximum expected values. For instance, '0:0:0:9' is
              an acceptable Galileo clock string, and will convert
              to the same number of ticks as '0:0:1:1'.

              Consecutive delimiters containing no intervening digits
              are treated as if they delimit zero components.

              Trailing zeros should always be included to match the
              length of the counter. For example, a Galileo clock
              count of '25684.90' should not be represented as
              '25684.9'.

              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.

Detailed_Output

     SCLKDP   is the double precision encoding of SCLKCH.

              The encoding is such that order and proximity will be
              preserved. That is, if t1, t2, and t3 are spacecraft
              clock times, and t1*, t2*, and t3* are their encodings,
              then if

                 t1 < t2 < t3, and

              t2 is closer to t1 than to t3, you will have the result
              that

                 t1* < t2* < t3*, and

              t2* is closer to t1* than to t3*.

              The units of encoded SCLK are "ticks since the start of
              the mission", where a "tick" is defined to be the
              shortest time increment expressible by a particular
              spacecraft's clock.

              Each clock string without partition number represents
              a certain number of ticks, but you need to include
              partition information to determine the relative
              position of that time in relation to the start of the
              mission.

              Since the end time of one partition is coincident
              with the begin time of the next, there are two
              different representations for this instant, and they
              will both yield the same encoding.

              For example, if partition 1 has an end time of t1, and
              partition 2 has a begin time of t2, then if we executed
              the code fragment

                 CALL SCENCD ( '1/t1', SC, X )
                 CALL SCENCD ( '2/t2', SC, Y )

              we would obtain X = Y.

Parameters

     MXPART   is the maximum number of spacecraft clock partitions
              expected in the kernel file for any one spacecraft.
              See the INCLUDE file sclk.inc for this parameter's
              value.

Exceptions

     1)  If the number of partitions in the kernel file for spacecraft
         SC exceeds the parameter MXPART, the error
         SPICE(TOOMANYPARTS) is signaled.

     2)  If any of the extracted clock components cannot be parsed as
         integers, or the string has too many components, or the value
         of one of the components is less than the offset value,
         an error is signaled by a routine in the call tree of this
         routine.

     If a partition number is included in the SCLK string, the
     following exceptions may occur:

     3)  If the partition number cannot be parsed as an integer, the
         error SPICE(BADPARTNUMBER) is signaled.

     4)  If the partition number is not in the range of the number of
         partitions found in the kernel pool, the error
         SPICE(BADPARTNUMBER) is signaled.

     5)  If the clock count does not fall in the boundaries of the
         specified partition, the error SPICE(NOTINPART) is
         signaled.

     If a partition number is not included in the SCLK string, the
     following exception may occur.

     6)  If the clock count does not fall in the boundaries of any
         partition found in the kernel pool, the error
         SPICE(NOPARTITION) is signaled.

     7)  If the partition delimiter (slash) is first found in the last
         position of SCLKCH, the error SPICE(INVALIDSCLKSTRING) is
         signaled.

Files

     A kernel file containing spacecraft clock partition information
     for the desired spacecraft must be loaded, using the routine
     FURNSH, 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. This routine provides a method of assigning a
     single double precision number to a spacecraft's clock count,
     given one of its character representations.

     The routine SCDECD performs the inverse operation of SCENCD,
     converting an encoded double precision number to character format.

     To convert the string to ticks since the start of the mission,
     SCENCD

        1) Converts the non-partition portion of the string to
           ticks, using the routine SCTIKS.

        2) Determines the partition number for the clock time,
           either by getting it directly from the input string, or
           determining the default partition if none was specified.

        3) Includes partition start and stop times, which are also
           measured in ticks, to compute the number of ticks
           from the beginning of the mission to the clock time.

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 SCENCD_EX1
              IMPLICIT NONE

        C
        C     Local parameters.
        C
        C     The instrument we want pointing for is the CASSINI
        C     spacecraft. The reference frame we want is
        C     J2000. The spacecraft is CASSINI.
        C
              INTEGER               SC
              PARAMETER           ( SC     = -82 )

              INTEGER               INST
              PARAMETER           ( INST   = -82000 )

              CHARACTER*(*)         REF
              PARAMETER           ( REF    = 'J2000' )

              CHARACTER*(*)         CK
              PARAMETER           ( CK     = '04153_04182ca_ISS.bc' )

              CHARACTER*(*)         SCLK
              PARAMETER           ( SCLK   = 'cas00071.tsc' )

              INTEGER               NPICS
              PARAMETER           ( NPICS  = 4 )

              CHARACTER*(*)         CLKTOL
              PARAMETER           ( CLKTOL = '1.0' )

              INTEGER               MAXLEN
              PARAMETER           ( MAXLEN = 30 )

        C
        C     Local variables.
        C
              CHARACTER*(25)        SCLKIN (4)
              CHARACTER*(25)        SCLKOUT

              DOUBLE PRECISION      CMAT   (3,3)
              DOUBLE PRECISION      TIMEIN
              DOUBLE PRECISION      TIMEOUT
              DOUBLE PRECISION      TOL

              INTEGER               I
              INTEGER               J
              INTEGER               K

              LOGICAL               FOUND

        C
        C     Set the input SCLK strings.
        C
              DATA                  SCLKIN /  '1/1465644279.0',
             .                                '1/1465644281.0',
             .                                '1/1465644351.0',
             .                                '1/1465644361.0'  /

        C
        C     Load the appropriate files. We need
        C
        C        1. CK file containing pointing data.
        C        2. Spacecraft clock kernel file.
        C
              CALL FURNSH ( CK   )
              CALL FURNSH ( SCLK )

        C
        C     Convert the tolerance string to ticks.
        C
              CALL SCTIKS ( SC, CLKTOL, TOL )

              DO I= 1, NPICS

                 CALL SCENCD ( SC, SCLKIN(I), TIMEIN )

                 CALL CKGP ( INST, TIMEIN,  TOL,  REF,
             .               CMAT, TIMEOUT, FOUND     )

                 WRITE(*,*)
                 WRITE(*,'(2A)') 'Input s/c clock count : ', SCLKIN(I)

                 IF ( FOUND ) THEN

                    CALL SCDECD ( SC, TIMEOUT, SCLKOUT )

                    WRITE(*,'(2A)') 'Output s/c clock count: ',
             .                                          SCLKOUT
                    WRITE(*,'(A)') 'Output C-Matrix:'

                    DO J = 1, 3

                       WRITE(*,'(3F21.15)') ( CMAT(J,K), K = 1, 3 )

                    END DO

                 ELSE

                    WRITE(*,'(A)') 'No pointing found.'

                 END IF

              END DO

              END


        When this program was executed on a Mac/Intel/gfortran/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

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     J.M. Lynch         (JPL)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)
     R.E. Thurman       (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.3.0, 21-NOV-2021 (NJB) (JDR)

        Now variables PSTART, PSTOP, and PTOTLS are saved. Made minor
        changes to formatting of code.

        Bug fix: out-of-range character positions of SCLKCH are
        no longer referenced.

        Edited the header to comply with NAIF standard. Added complete
        code example based on existing example fragments using PDS
        archived CASSINI data.

        Removed wrong reference to routine CLPOOL from SCLKCH detailed
        description and $Files section, and reference to nonexistent
        TIKSnn routines.

        Removed unnecessary $Revisions section.

    SPICELIB Version 1.2.0, 28-FEB-2014 (BVS)

        Added FAILED checks to prevent passing uninitialized values to
        ANINT, which can causing numeric exceptions on some
        environments.

    SPICELIB Version 1.1.0, 05-FEB-2008 (NJB)

        The values of the parameter MXPART is now
        provided by the INCLUDE file sclk.inc.

    SPICELIB Version 1.0.2, 22-AUG-2006 (EDW)

        Replaced references to LDPOOL with references
        to FURNSH.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 03-SEP-1990 (JML) (RET)
Fri Dec 31 18:36:45 2021