pub fn scdecd(
ctx: &mut SpiceContext<'_>,
sc: i32,
sclkdp: f64,
sclkch: &mut str,
) -> Result<()>Expand description
Decode spacecraft clock
Convert a double precision encoding of spacecraft clock time into a character representation.
§Required Reading
§Brief I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
SC I NAIF spacecraft identification code.
SCLKDP I Encoded representation of a spacecraft clock count.
SCLKCH O Character representation of a clock count.
MXPART P Maximum number of spacecraft clock partitions.§Detailed Input
SC is the NAIF integer code of the spacecraft whose
clock's time is being decoded.
SCLKDP is the double precision encoding of a clock time in
units of ticks since the spacecraft clock start time.
This value does reflect partition information.
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
If SCLKDP contains a fractional part the result
is the same as if SCLKDP had been rounded to the
nearest whole number.§Detailed Output
SCLKCH is the character representation of the clock count.
The exact form that SCLKCH takes depends on the
spacecraft.
Nevertheless, SCLKCH will have the following general
format:
'pp/sclk_string'
'pp' is an integer greater than or equal to one and
represents a "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
before calling SCDECD.
The routine SCPART may be used to read the partition
start and stop times, in encoded units of ticks, from
the kernel file.
Since the end time of one partition is coincident with
the begin time of the next, two different time strings
with different partition numbers can encode into the
same value.
For example, if partition 1 ends at time t1, and
partition 2 starts at time t2, then
'1/t1' and '2/t2'
will be encoded into the same value, say X. SCDECD
always decodes such values into the latter of the
two partitions. In this example,
CALL SCDECD ( X, SC, CLKSTR )
will result in
CLKSTR = '2/t2'.
'sclk_string' is a spacecraft specific clock string,
typically consisting of a number of components
separated by delimiters.
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: ' ' ':' ',' '-' '.'
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.§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 kernel variables required by this routine are unavailable,
an error is signaled by a routine in the call tree of this
routine. SCLKCH will be returned as a blank string in this
case.
2) If the number of partitions in the kernel file for spacecraft
SC exceeds the parameter MXPART, the error
SPICE(TOOMANYPARTS) is signaled. SCLKCH will be returned
as a blank string in this case.
3) If the encoded value does not fall in the boundaries of the
mission, the error SPICE(VALUEOUTOFRANGE) is signaled.
SCLKCH will be returned as a blank string in this case.
4) If the declared length of SCLKCH is not large enough to
contain the output clock string, the error
SPICE(SCLKTRUNCATED) is signaled by either this routine or a
routine in the call tree of this routine. On output SCLKCH
will contain a portion of the truncated clock string.§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. The routine SCENCD provides a method of
assigning a single double precision number to a spacecraft's
clock count, given one of its character representations.
This routine performs the inverse operation to SCENCD, converting
an encoded double precision number to character format.
To convert the number of ticks since the start of the mission to
a clock format character string, SCDECD:
1) Determines the spacecraft clock partition that TICKS falls
in.
2) Subtracts off the number of ticks occurring in previous
partitions, to get the number of ticks since the beginning
of the current partition.
3) Converts the resulting ticks to clock format and forms the
string
'partition_number/clock_string'§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 SCDECD_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
1) Assumes that an SCLK kernel file appropriate for the clock
designated by SC is loaded in the kernel pool at the time
this routine is called.§Author and Institution
N.J. Bachman (JPL)
J. Diaz del Rio (ODC Space)
J.M. Lynch (JPL)
W.L. Taber (JPL)
R.E. Thurman (JPL)
E.D. Wright (JPL)§Version
- SPICELIB Version 2.2.0, 18-NOV-2021 (NJB) (JDR)
Now variables PSTART, PSTOP, and PTOTLS are saved. Made minor
changes to formatting of code.
Edited the header to comply with NAIF standard. Added complete
code example based on existing example fragments using PDS
archived CASSINI data.
Added FAILED() call after SCFMT call.
Removed unnecessary entries in $Revisions section.
- SPICELIB Version 2.1.0, 05-FEB-2008 (NJB)
Values of parameter MXPART and PARTLN are now
provided by the INCLUDE file sclk.inc.
- SPICELIB Version 2.0.1, 22-AUG-2006 (EDW)
Replaced references to LDPOOL with references
to FURNSH.
- SPICELIB Version 2.0.0, 17-APR-1992 (JML) (WLT)
The routine was changed to signal an error when SCLKCH is
not long enough to contain the output spacecraft clock
string.
FAILED is now checked after calling SCPART.
References to CLPOOL were deleted.
Miscellaneous minor updates to the header were performed.
Comment section for permuted index source lines was added
following the header.
- SPICELIB Version 1.0.0, 06-SEP-1990 (JML) (RET)§Revisions
- SPICELIB Version 2.0.0, 17-APR-1992 (JML) (WLT)
The routine was changed to signal an error when SCLKCH is
not long enough to contain the output spacecraft clock
string. Previously, the SCLK routines simply truncated
the clock string on the right. It was determined that
since this truncation could easily go undetected by the
user ( only the leftmost field of a clock string is
required when clock string is used as an input to a
SCLK routine ), it would be better to signal an error
when this happens.
FAILED is checked after calling SCPART in case an
error has occurred reading the kernel file and the
error action is not set to 'abort'.
References to CLPOOL were deleted.
Miscellaneous minor updates to the header were performed.
Comment section for permuted index source lines was added
following the header.