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: http://www.stsci.edu/~sontag/spicedocs/cspice/sctiks_c.html
Дата изменения: Sat Dec 17 06:09:40 2005 Дата индексирования: Mon Apr 11 00:08:42 2016 Кодировка: Поисковые слова: agn |
Convert a spacecraft clock format string to number of "ticks".
SCLK
Variable I/O Description -------- --- -------------------------------------------------- sc I NAIF spacecraft identification code. clkstr I Character representation of a spacecraft clock. ticks O Number of ticks represented by the clock string.
sc is the NAIF ID number for the spacecraft whose clock string is being converted. clkstr is a character string representing a spacecraft clock time, WITHOUT PARTITION NUMBER. 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 the following characters: " " "." ":" "," "-" Any number of spaces may 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.
ticks is the number of ticks represented by the spacecraft clock string. A tick is defined to be the smallest time increment expressible by the spacecraft clock. An analogy may be drawn between a spacecraft clock and a standard wall clock, measuring hours, minutes and seconds. The number of ticks represented by the wall clock string hh:mm:ss would be the number of seconds represented by that time. For example: 00:00:10 would convert to 10 00:01:00 would convert to 60 00:10:00 would convert to 600 01:00:00 would convert to 3600 01:01:00 would convert to 3660 See the Examples section below for examples for actual spacecraft clocks.
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Note the important difference between scencd_c and sctiks_c. scencd_c converts a clock string to the number of ticks it represents since the beginning of the mission, and so uses partition information. sctiks_c just converts to absolute ticks.
sctiks_c is used as part of the process of encoding spacecraft clock by scencd_c, though sctiks_c does not process any partition informa- tion. Another use of sctiks_c, however, is to convert a clock measurement to ticks for use as a tolerance for the CK reader ckgp_c. /. Get the pointing from a CK file of the VGR 1 narrow angle image corresponding to a particular SCLK count. Load the CK file and the kernel file containing SCLK partition information for scencd_c. ./ cklpf_c ( "vgr1na.ck", &handle ); ldpool_c ( "sclk.ker" ); /. Get the right ID numbers. ./ sc = -31; instr = -31001; /. The SCLK string includes a partition number. Pictures are never shuttered at intervals smaller than 1 MOD60 count from each other. So use 1 MOD60 count as the time tolerance. ./ clkstr = "1/20556:14:768"; tolstr = " 0:01:000"; /. Encode the clock string and the tolerance. ./ scencd_c ( sc, clkstr, &sclk ); sctiks_c ( sc, tolstr, &tol ); /. Get the pointing from the C-kernel. ./ ckgp_c ( instr, sclk, tol, ref, cmat, &clkout, &found ); Below are some examples illustrating various clock string inputs and the resulting outputs for the Galileo spacecraft. See the SCLK required reading for a detailed description of the Galileo clock format. CLKSTR TICKS ---------------- -------------------- "0:0:0:1" 1 "0:0:1" 8 "0:1" 80 "1" 7280 "1 0 0 0" 7280 "1,0,0,0" 7280 "1:90" 14480 "1:9" 8000 "1:09" 8000 "0-0-10" 80 |-- Third component is supposed "0-1-0" 80 | to be a mod-10 count. "0/1/0" Error: "/" is not an accepted delimiter. "1: 00 : 0 : 1" 7281 "1:::1" 7281 "1.1.1.1.1" Error: Too many components "1.1.1.1." Error: The last delimiter signals that a fifth component will follow. The following examples are for the Voyager 2 spacecraft. Note that the last component of the Voyager clock has an offset value of 1. CLKSTR TICKS ---------------- -------------------- "0.0.001" 0 "0:0:002" 1 "0:01" 800 "1" 48000 "1.0" 48000 "1.0.0" Error: The 3rd component is never 0. "0.0:100" 99 "0-60-1" 48000 "1-1-1" 48800 "1-1-2" 48801
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1) If the spacecraft clock type is not supported then the error SPICE(NOTSUPPORTED) is signalled. 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, then the error is diagnosed by routines called by this routine. 3) Invalid spacecraft ID's are not diagnosed.
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J.M. Lynch (JPL) R.E. Thurman (JPL)
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-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)
convert spacecraft_clock string to ticks