| spkw02_c |
|
Table of contents
Procedure
spkw02_c ( Write SPK segment, type 2 )
void spkw02_c ( SpiceInt handle,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
SpiceDouble intlen,
SpiceInt n,
SpiceInt polydg,
ConstSpiceDouble cdata [],
SpiceDouble btime )
AbstractWrite a type 2 segment to an SPK file. Required_ReadingNAIF_IDS SPC SPK KeywordsEPHEMERIS Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- MAXDEG P Maximum degree of Chebyshev expansions. TOLSCL P Scale factor used to compute time bound tolerance. handle I Handle of an SPK file open for writing. body I Body code for ephemeris object. center I Body code for the center of motion of the body. frame I The reference frame of the states. first I First valid time for which states can be computed. last I Last valid time for which states can be computed. segid I Segment identifier. intlen I Length of time covered by logical record. n I Number of coefficient sets. polydg I Chebyshev polynomial degree. cdata I Array of Chebyshev coefficients. btime I Begin time of first logical record. Detailed_Input
handle is the DAF handle of an SPK file to which a type 2
segment is to be added. The SPK file must be open for
writing.
body is the NAIF integer code for an ephemeris object whose
state relative to another body is described by the
segment to be created.
center is the NAIF integer code for the center of motion of the
object identified by `body'.
frame is the NAIF name for a reference frame relative to which
the state information for `body' is specified.
first,
last are the start and stop times of the time interval over
which the segment defines the state of body.
segid is the segment identifier. An SPK segment identifier may
contain up to 40 characters.
intlen is the length of time, in seconds, covered by each set of
Chebyshev polynomial coefficients (each logical record).
Each set of Chebyshev coefficients must cover this fixed
time interval, `intlen'.
n is the number of sets of Chebyshev polynomial
coefficients for coordinates (number of logical records)
to be stored in the segment. There is one set of
Chebyshev coefficients for each time period.
polydg is the degree of each set of Chebyshev polynomials used
to represent the ephemeris information. That is, the
number of Chebyshev coefficients per coordinate minus
one. `polydg' must not exceed MAXDEG (see -Parameters
below).
cdata is a time-ordered array of `n' sets of Chebyshev polynomial
coefficients to be placed in the segment of the SPK file.
Each set has size setsz = 3*(polydg+1). The coefficients
are stored in `cdata' in order as follows:
the (polydg + 1) coefficients for the first
coordinate of the first logical record,
the coefficients for the second coordinate,
the coefficients for the third coordinate,
the coefficients for the first coordinate for
the second logical record, ...
and so on.
btime is the begin time (seconds past J2000 TDB) of first set
of Chebyshev polynomial coefficients (first logical
record). `first' is an appropriate value for `btime'.
Detailed_OutputNone. The routine writes to the SPK file referred to by `handle' a type 02 SPK segment containing the data in `cdata'. See the -Particulars section for details about the structure of a type 02 SPK segment. Parameters
The parameters below are declared in the Fortran include file
spk02.inc, which is part of the Fortran SPICE Toolkit (aka
SPICELIB). The values of those parameters are used in CSPICE code
generated by running f2c on SPICELIB source code. They are not
directly referenced by code in this module.
MAXDEG is the maximum allowed degree of the input
Chebyshev expansions.
The value of MAXDEG is 27.
TOLSCL is a tolerance scale factor (also called a
"relative tolerance") used for time coverage bound
checking. TOLSCL is unitless. TOLSCL produces a
tolerance value via the formula
TOL = TOLSCL * max( abs(first), abs(last) )
where `first' and `last' are the coverage time
bounds of a type 2 segment, expressed as seconds
past J2000 TDB.
The resulting parameter TOL is used as a tolerance
for comparing the input segment descriptor time
bounds to the first and last epoch covered by the
sequence of time intervals defined by the inputs
to spkw02_c:
btime
intlen
n
The value of TOLSCL is 1.e-13.
Exceptions
1) If the number of sets of coefficients is not positive, the
error SPICE(NUMCOEFFSNOTPOS) is signaled by a routine in the
call tree of this routine.
2) If the interval length is not positive, the error
SPICE(INTLENNOTPOS) is signaled by a routine in the call tree
of this routine.
3) If the name of the reference frame is not recognized, the
error SPICE(INVALIDREFFRAME) is signaled by a routine in the
call tree of this routine.
4) If segment stop time is not greater then the begin time, the
error SPICE(BADDESCRTIMES) is signaled by a routine in the
call tree of this routine.
5) If the start time of the first record exceeds the descriptor
begin time by more than a computed tolerance, or if the end
time of the last record precedes the descriptor end time by
more than a computed tolerance, the error SPICE(COVERAGEGAP)
is signaled by a routine in the call tree of this routine. See
the -Parameters section above for a description of the
tolerance.
6) If the input degree `polydg' is less than 0 or greater than
MAXDEG, the error SPICE(INVALIDDEGREE) is signaled by a
routine in the call tree of this routine.
7) If the last non-blank character of `segid' occurs past index 40,
or if `segid' contains any nonprintable characters, an error is
signaled by a routine in the call tree of this routine.
8) If any of the `frame' or `segid' input string pointers is
null, the error SPICE(NULLPOINTER) is signaled.
9) If any of the `frame' or `segid' input strings has zero
length, the error SPICE(EMPTYSTRING) is signaled.
FilesA new type 2 SPK segment is written to the SPK file attached to handle. Particulars
This routine writes an SPK type 2 data segment to the designated
SPK file, according to the format described in the SPK Required
Reading.
Each segment can contain data for only one target, central body,
and reference frame. The Chebyshev polynomial degree and length
of time covered by each logical record are also fixed. However,
an arbitrary number of logical records of Chebyshev polynomial
coefficients can be written in each segment. Minimizing the
number of segments in an SPK file will help optimize how the SPICE
system accesses the file.
The ephemeris data supplied to the type 2 SPK writer is packed
into an array as a sequence of records. The logical data records
are stored contiguously:
+----------+
| Record 1 |
+----------+
| Record 2 |
+----------+
...
+----------+
| Record n |
+----------+
The contents of an individual record are:
+--------------------------------------+
| Coeff set for X position component |
+--------------------------------------+
| Coeff set for Y position component |
+--------------------------------------+
| Coeff set for Z position component |
+--------------------------------------+
Each coefficient set has the structure:
+--------------------------------------+
| Coefficient of T_0 |
+--------------------------------------+
| Coefficient of T_1 |
+--------------------------------------+
...
+--------------------------------------+
| Coefficient of T_POLYDG |
+--------------------------------------+
Where T_n represents the Chebyshev polynomial
of the first kind of degree n.
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) This example demonstrates how to create an SPK type 2 kernel
containing only one segment, given a set of Chebychev
coefficients and their associated epochs.
Example code begins here.
/.
Program spkw02_ex1
./
#include "SpiceUsr.h"
int main( )
{
/.
Define the segment identifier parameters.
./
#define SPK2 "spkw02_ex1.bsp"
#define REF "J2000"
#define BODY 3
#define CENTER 10
#define CHBDEG 2
#define NRECS 4
#define RECSIZ ( 3*(CHBDEG+1) )
/.
Local variables.
./
SpiceChar * ifname;
SpiceChar * segid;
SpiceDouble first;
SpiceDouble intlen;
SpiceDouble last;
SpiceInt handle;
SpiceInt ncomch;
/.
Define the coefficients.
./
SpiceDouble recrds [NRECS][RECSIZ] = {
{1.0101, 1.0102, 1.0103,
1.0201, 1.0202, 1.0203,
1.0301, 1.0302, 1.0303},
{2.0101, 2.0102, 2.0103,
2.0201, 2.0202, 2.0203,
2.0301, 2.0302, 2.0303},
{3.0101, 3.0102, 3.0103,
3.0201, 3.0202, 3.0203,
3.0301, 3.0302, 3.0303},
{4.0101, 4.0102, 4.0103,
4.0201, 4.0202, 4.0203,
4.0301, 4.0302, 4.0303} };
/.
Set the start and end times of interval covered by
segment, and the length of time covered by logical
record.
./
first = 100.0;
last = 500.0;
intlen = 100.0;
/.
`ncomch' is the number of characters to reserve for the
kernel's comment area. This example doesn't write
comments, so set to zero.
./
ncomch = 0;
/.
Internal file name and segment ID.
./
ifname = "Type 2 SPK internal file name.";
segid = "SPK type 2 test segment";
/.
Open a new SPK file.
./
spkopn_c ( SPK2, ifname, ncomch, &handle );
/.
Write the segment.
./
spkw02_c ( handle, BODY, CENTER, REF, first, last,
segid, intlen, NRECS, CHBDEG, recrds, first );
/.
Close the SPK file.
./
spkcls_c ( handle );
return ( 0 );
}
When this program is executed, no output is presented on
screen. After run completion, a new SPK type 2 exists in
the output directory.
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) K.S. Zukor (JPL) Version
-CSPICE Version 2.0.1, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Added complete
example code from existing fragment.
Extended "polydg" and "cdata" arguments description to provide the
size of the Chebyshev polynomials sets. Moved the details of the SPK
structure from "cdata" argument description to -Particulars section.
Added entry #4 in -Exceptions section.
-CSPICE Version 2.0.0, 09-JAN-2014 (NJB)
Relaxed test on relationship between the time bounds of the
input record set (determined by `btime', `intlen', and `n') and
the descriptor bounds `first' and `last'. Now the descriptor
bounds may extend beyond the time bounds of the record set by a
ratio computed using the parameter TOLSCL (see -Parameters above
for details). Added checks on input polynomial degree.
-CSPICE Version 1.0.0, 21-JUL-1999 (NJB) (KSZ)
Index_Entrieswrite SPK type_2 data segment |
Fri Dec 31 18:41:13 2021