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scencd_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

   void scencd_c ( SpiceInt           sc, 
                   ConstSpiceChar   * sclkch, 
                   SpiceDouble      * sclkdp ) 

Abstract

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

Required_Reading

 
   SCLK 
 

Keywords

 
   CONVERSION 
   TIME 
 

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_c. 
 
              The routine scpart_c 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 signalled. 
 
 
              "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 
 
                 scencd_c ( "1/t1", sc, &x ); 
                 scencd_c ( "2/t2", sc, &y );
                 
              The we would obtain x = y. 
 
              The individual routines tiksNN_c, where NN is the 
              clock type code, contain more detailed information 
              on the conversion process. 
 

Parameters

 
   MXPART     is the maximum number of spacecraft clock partitions 
              expected in the kernel file for any one spacecraft. 
              MXPART is currently set to 9999.
 

Exceptions

 
   1) If the number of partitions in the kernel file for spacecraft 
      sc exceeds the parameter MXPART, the error 
      SPICE(TOOMANYPARTS) is signalled. 
 
 
   If a partition number is included in the SCLK string, the 
   following exceptions may occur: 
 
   2) If the partition number cannot be parsed as an integer, the 
      error SPICE(BADPARTNUMBER) is signalled. 
 
   3) If the partition number is not in the range of the number of 
      partitions found in the kernel pool, the error 
      SPICE(BADPARTNUMBER) is signalled. 
 
   4) If the clock count does not fall within the boundaries of the 
      specified partition, the error SPICE(NOTINPART) is signalled. 
 
   If a partition number is not included in the SCLK string, the 
   following exception may occur. 
 
   5) If the clock count does not fall within the boundaries of any 
      partition found in the kernel pool, the error SPICE(NOPARTITION)
      is signalled. 
 
 
   The following error is signalled by a routine called by scencd_c.
 
   6)  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, then 
       the error SPICE(INVALIDSCLKSTRING) is signalled. 
 

Files

 
   A kernel file containing spacecraft clock partition information 
   for the desired spaceraft 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.  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_c performs the inverse operation of scencd_c, 
   converting an encoded double precision number to character format. 
 
   To convert the string to ticks since the start of the mission, 
   scencd_c 
 
      1) Converts the non-partition portion of the string to 
         ticks, using the routine sctiks_c. 
 
      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

 
   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 Voyager 2 narrow angle camera 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. 
 
      #include <stdio.h>
      #include "SpiceUsr.h"
      
      void main()
      {
         /. 
         The instrument we want pointing for is the Voyager 2 
         narrow angle camera.  The reference frame we want is 
         J2000. The spacecraft is Voyager 2. 
         ./
         
         #define  SC         -32
         #define  INST       -32001
         #define  REF        "J2000"
         #define  CK         "/kernels/voyager2/ck/vg2_jup_qmw_na.bc"
         #define  SCLK       "/kernels/voyager2/sclk/vg200004.tsc"
         #define  NPICS      4 
         #define  CLKTOL     "0:01:001"
         #define  MAXLEN     30
      
         SpiceBoolean       found;
      
         SpiceChar          sclkin [4][25] = { {"2 / 20538:39:768"}, 
                                               {"2 / 20543:21:768"}, 
                                               {"2 / 20550:37"    }, 
                                               {"2 / 20561:59"    } };      
         SpiceChar          sclkout[25];
      
         SpiceDouble        tol;
         SpiceDouble        timein;
         SpiceDouble        timeout; 
         SpiceDouble        cmat   [3][3];
      
         SpiceInt           handle;
         SpiceInt           i;
      
      
         /.
         Load the appropriate files. We need 
         
            1) CK file containing pointing data. 
            2) Spacecraft clock kernel file, for scencd_c and SCDECD. 
         ./
         
         cklpf_c  ( CK,  &handle );
         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       );
      
            scdecd_c ( SC, timeout, MAXLEN, sclkout );  
      
            if ( found )
            {
               printf ( "\n"
                        "Input  s/c clock count: %s\n"
                        "Output s/c clock count: %s\n"
                        "Output C-Matrix:          \n"
                        "%25.16f   %25.16f   %25.16f\n"   
                        "%25.16f   %25.16f   %25.16f\n"   
                        "%25.16f   %25.16f   %25.16f\n"
                        "\n",   
                        sclkin[i],
                        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 ( "\n"
                        "Input  s/c clock count: %s\n"
                        "No pointing found.\n",   
                        sclkin[i]                     );
            }
         }
      
      }

 
   The output from such a program might look like: 
 
 
          Input  s/c clock count:  2 / 20538:39:768 
          Output s/c clock count:  2/20538:39:768 
          Output C-Matrix:  "first C-matrix" 
 
          Input  s/c clock count:  2 / 20543:21:768 
          Output s/c clock count:  2/20543:22:768 
          Output C-Matrix:  "second C-matrix" 
 
          Input  s/c clock count:  2 / 20550:37 
          Output s/c clock count:  2/20550:36:768 
          Output C-Matrix:  "third C-matrix" 
 
          Input  s/c clock count:  2 / 20561:59 
          Output s/c clock count:  2/20561:58:768 
          Output C-Matrix:  "fourth C-matrix" 
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   J.M. Lynch   (JPL) 
   R.E. Thurman (JPL) 
 

Version

   -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 1.1.1, 14-AUG-2006 (EDW)

      Replace mention of ldpool_c with furnsh_c.
 
   -CSPICE Version 1.1.0, 08-FEB-1998 (NJB)  
   
       References to C2F_CreateStr_Sig were removed; code was
       cleaned up accordingly.  String checks are now done using
       the macro CHKFSTR.
       
   -CSPICE Version 1.0.0, 25-OCT-1997 (NJB)
   
      Based on SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

Index_Entries

 
   encode spacecraft_clock 
 
Wed Apr  5 17:54:42 2017