| spkw20_c |
|
Table of contents
Procedure
spkw20_c ( Write SPK segment, type 20 )
void spkw20_c ( SpiceInt handle,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
SpiceDouble intlen,
SpiceInt n,
SpiceInt polydg,
ConstSpiceDouble cdata[],
SpiceDouble dscale,
SpiceDouble tscale,
SpiceDouble initjd,
SpiceDouble initfr )
AbstractWrite a type 20 segment to an SPK file. Required_ReadingDAF NAIF_IDS TIME SPK KeywordsEPHEMERIS Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
handle I Handle of SPK file open for writing.
body I NAIF code for ephemeris object.
center I NAIF code for the center of motion of the body.
frame I Reference frame name.
first I Start time of interval covered by segment.
last I End time of interval covered by segment.
segid I Segment identifier.
intlen I Length of time covered by logical record (days).
n I Number of logical records in segment.
polydg I Chebyshev polynomial degree.
cdata I Array of Chebyshev coefficients and positions.
dscale I Distance scale of data.
tscale I Time scale of data.
initjd I Integer part of begin time (TDB Julian date) of
first record.
initfr I Fractional part of begin time (TDB Julian date) of
first record.
MAXDEG P Maximum allowed degree of Chebyshev expansions.
DTOL P Absolute tolerance for coverage bound checking.
TOLSCL P Tolerance scale for coverage bound checking.
Detailed_Input
handle is the DAF handle of an SPK file to which a type 20
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 the
object identified by `body'.
segid is a segment identifier. An SPK segment identifier
may contain up to 40 characters, not counting the
terminating null character.
intlen is the length of time, in TDB Julian days, covered
by each set of Chebyshev polynomial coefficients
(each logical record).
n is the number of number of logical records to be
stored in the segment. There is one logical record
for each time period. Each logical record contains
three sets of Chebyshev coefficients---one for each
coordinate---and three position vector components.
polydg is the degree of each set of Chebyshev
polynomials, i.e. the number of Chebyshev
coefficients per coordinate minus one. `polydg' must
be less than or equal to the parameter MAXDEG.
cdata is an array containing all the sets of Chebyshev
polynomial coefficients and position components to
be placed in the new segment of the SPK file.
There are three sets of coefficients and position
components for each time interval covered by the
segment.
The coefficients and position components are
stored in `cdata' in order as follows:
the (degree + 1) coefficients for the first
coordinate of the first logical record,
followed by the X component of position at the
first interval midpoint.
the coefficients for the second coordinate,
followed by the Y component of position at the
first interval midpoint.
the coefficients for the third coordinate,
followed by the Z component of position at the
first interval midpoint.
the coefficients for the first coordinate for
the second logical record, followed by the X
component of position at the second interval
midpoint.
and so on.
A diagram follows:
+--------------------------------------+
| Coeff set for X velocity component |
+--------------------------------------+
| X position component |
+--------------------------------------+
| Coeff set for Y velocity component |
+--------------------------------------+
| Y position component |
+--------------------------------------+
| Coeff set for Z velocity component |
+--------------------------------------+
| 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.
dscale,
tscale are, respectively, the distance scale of the input
position and velocity data in km, and the time
scale of the input velocity data in TDB seconds.
For example, if the input distance data have units
of astronomical units (AU), `dscale' should be set
to the number of km in one AU. If the input
velocity data have time units of Julian days, then
`tscale' should be set to the number of seconds per
Julian day (86400).
initjd is the integer part of the Julian ephemeris date of
initial epoch of the first record. `initjd' may be
less than, equal to, or greater than the initial
epoch.
initfr is the fractional part of the Julian ephemeris date
of initial epoch of the first record. `initfr' has
units of Julian days. `initfr' has magnitude strictly
less than 1 day. The sum
initjd + initfr
equals the Julian ephemeris date of the initial
epoch of the first record.
Detailed_OutputNone. This routine writes data to an SPK file. Parameters
The parameters listed below are not used directly in this
routine; they are used by the underlying SPICELIB code that
has been translated to C via f2c.
MAXDEG is the maximum allowed degree of the input
Chebyshev expansions. MAXDEG is declared in the
SPICELIB Fortran INCLUDE file spk20.inc.
The current value of MAXDEG is 50.
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 20 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
initjd
initfr
intlen
n
See the -Exceptions section below for a description
of the error check using this tolerance.
The current value of TOLSCL is 1e-13.
Exceptions
1) If the number of sets of coefficients is not positive, the
error SPICE(INVALIDCOUNT) 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 than or equal to 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 either the distance or time scale is non-positive, the
error SPICE(NONPOSITIVESCALE) is signaled by a routine in the
call tree of this routine.
9) If any of the `frame' or `segid' input string pointers is
null, the error SPICE(NULLPOINTER) is signaled.
10) If any of the `frame' or `segid' input strings has zero
length, the error SPICE(EMPTYSTRING) is signaled.
FilesA new type 20 SPK segment is written to the SPK file attached to `handle'. ParticularsThis routine writes an SPK type 20 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. Examples
Suppose that you have in an array `cdata' sets of Chebyshev
polynomial coefficients and position vectors representing the state
of the moon (NAIF ID = 301), relative to the Earth-moon barycenter
(NAIF ID = 3), in the J2000 reference frame, and you want to put
these into a type 20 segment in an existing SPK file. The following
code could be used to add one new type 20 segment. To add multiple
segments, put the call to spkw20_c in a loop.
#include "SpiceUsr.h"
.
.
.
/.
First open the SPK file and get a handle for it.
./
spkopa_c ( spknam, &handle );
/.
Create a segment identifier.
./
segid = "MY_SAMPLE_SPK_TYPE_20_SEGMENT";
/.
Note that the interval length `intlen' has units
of Julian days. The start time of the first record
is expressed using two inputs: integer and fractional
portions of the Julian ephemeris date of the start
time.
Write the segment.
./
spkw20_c ( handle, 301, 3, "J2000",
first, last, segid, intlen,
n, polydg, cdata, dscale,
tscale, initjd, initfr );
/.
Close the file.
./
spkcls_c ( handle );
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) Version
-CSPICE Version 1.0.1, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard.
-CSPICE Version 1.0.0, 23-DEC-2013 (NJB)
Index_Entrieswrite SPK type_20 data segment |
Fri Dec 31 18:41:13 2021