void sctiks_c ( SpiceInt sc,
ConstSpiceChar * clkstr,
SpiceDouble * ticks )
Convert a spacecraft clock format string to number of "ticks".
SCLK
CONVERSION
TIME
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.
None.
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.
None.
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 );
furnsh_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
None.
None.
J.M. Lynch (JPL)
R.E. Thurman (JPL)
-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)
convert spacecraft_clock string to ticks
Link to routine sctiks_c source file sctiks_c.c
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