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Convert encoded spacecraft clock ticks to character clock format.
SCLK
Variable I/O Description -------- --- -------------------------------------------------- sc I NAIF spacecraft identification code. ticks I Encoded representation of a spacecraft clock count. lenout I Maximum allowed length of output string. clkstr O Character representation of a clock count.
sc is the NAIF ID number for the spacecraft whose clock's time is being decoded. ticks is the double precision encoding of a clock time in units of ticks. Partition information is not reflected in this value. 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 01:01:00 3660 If ticks contains a fractional part the result is the same as if ticks had been rounded to the nearest whole number. See the Examples section below for examples of actual spacecraft clock conversions. lenout The allowed length of the output string. This length must large enough to hold the 'clkstr' string plus the null terminator. If the output string is expected to have x characters, 'lenout' must be x + 1.
clkstr is the spacecraft clock character string corresponding to ticks. Partition information is not included in clkstr. Using Galileo as an example, the full format clock string 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.
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The routine sctiks_c performs the inverse operation to scfmt_c, converting from clock format to number of ticks. Note the important difference between scfmt_c and scdecd_c. scdecd_c converts some number of ticks since the spacecraft clock start time to a character string which includes a partition number. scfmt_c, which is called by scdecd_c, does not make use of partition information.
The following program fragment finds partition start and stop times for the Galileo spacecraft from a spacecraft clock partition kernel file, called sclk.ker. Since those times are always returned in units of ticks, the program uses scfmt_c to print the times in Galileo clock format. #include <stdio.h> #include "SpiceUsr.h" #define MXPART 50 #define MAXLEN 30 SpiceChar start [ 30 ]; SpiceChar stop [ 30 ]; SpiceDouble pstart [ MXPART ]; SpiceDouble pstop [ MXPART ]; SpiceInt sc = -77; SpiceInt i; SpiceInt nparts; ldpool_c ( "sclk.ker" ); scpart_c ( sc, &nparts, pstart, pstop ); for ( i = 0; i < nparts; i++ ) { scfmt_c ( sc, pstart[ i ], MAXLEN, start ); scfmt_c ( sc, pstop [ i ], MAXLEN, stop ); printf ( "\n" "partition %d: \n" "start = %s\n" "stop = %s\n", i, start, stop ); } Below are some examples illustrating various input numbers of ticks and the resulting clock string outputs for the Galileo spacecraft. TICKS CLKSTR ---------------- -------------------- -1 Error: Ticks must be a positive number 0 "0:00:0:0" 1 "0:00:0:1" 1.3 "0:00:0:1" 1.5 "0:00:0:2" 2 "0:00:0:2" 7 "0:00:0:7" 8 "0:00:1:0" 80 "0:01:0:0" 88 "0:01:1:0" 7279 "0:90:9:7" 7280 "1:00:0:0" 1234567890 "169583:45:6:2" The following examples are for the Voyager 2 spacecraft. Note that the third component of the Voyager clock has an offset value of one. TICKS CLKSTR ---------------- -------------------- -1 Error: Ticks must be a positive number 0 "00000 00 001" 1 "00000 00 002" 1.3 "00000:00:002" 1.5 "00000.00.003" 2 "00000-00-003" 799 "00000,00,800" 800 "00000 01 001" 47999 "00000 59 800" 48000 "00001 00 001" 3145727999 "65535 59 800"
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1) If the data type for the spacecraft is not supported then the error SPICE(NOTSUPPORTED) is signaled. 2) If the value for ticks is negative, the error is diagnosed by routines called by this routine. 3) If the SCLK kernel file does not contain data for the spacecraft specified by sc, then the error is diagnosed by routines called by this routine. 4) If the output string pointer is null, the error SPICE(NULLPOINTER) is signaled. 5) If the output string has length less than two characters, it is too short to contain one character of output data plus a null terminator, so it cannot be passed to the underlying Fortran routine. In this event, the the error SPICE(STRINGTOOSHORT) is signaled. 6) If the length of clkstr (indicated by lenout) is at least two characters but not large enough to contain the output clock string, the error is diagnosed by a routine called by this routine.
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N.J. Bachman (JPL) J.M. Lynch (JPL) R.E. Thurman (JPL)
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-CSPICE Version 1.1.2, 01-OCT-2003 (EDW) Added description of the 'lenout' input in the Detailed_Input section. -CSPICE Version 1.1.1, 26-MAR-2003 (NJB) Fixed description of exception (6): replaced "lenout-1" with "lenout." -CSPICE Version 1.1.0, 09-FEB-1998 (NJB) Re-implemented routine without dynamically allocated, temporary strings. Updated the Exceptions header section. -CSPICE Version 1.0.0, 25-OCT-1997 (NJB) Based on SPICELIB Version 1.0.1, 17-APR-1992 (JML) (WLT)
convert spacecraft_clock ticks to character clock format