| spkw17_c |
|
Table of contents
Procedure
spkw17_c ( SPK, write a type 17 segment )
void spkw17_c ( SpiceInt handle,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
SpiceDouble epoch,
ConstSpiceDouble eqel [9],
SpiceDouble rapol,
SpiceDouble decpol )
AbstractWrite an SPK segment of type 17 given a type 17 data record. Required_ReadingSPK KeywordsEPHEMERIS Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- 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. epoch I Epoch of elements in seconds past J2000. eqel I Array of equinoctial elements. rapol I Right Ascension of the reference plane's pole. decpol I Declination of the reference plane's pole. Detailed_Input
handle is the file handle of an SPK file that has been
opened for writing.
body is the NAIF ID for the body whose states are
to be recorded in the SPK file.
center is the NAIF ID for the center of motion associated
with `body'.
frame is the reference frame that states are referenced to,
for example "J2000".
first,
last are the bounds on the ephemeris times, expressed as
seconds past J2000.
segid is the segment identifier. An SPK segment identifier
may contain up to 40 characters.
epoch is the epoch of equinoctial elements in seconds
past the J2000 epoch.
eqel is an array of 9 double precision numbers that
are the equinoctial elements for some orbit relative
to the equatorial frame of a central body.
Note: The Z-axis of the equatorial frame is the
direction of the pole of the central body relative
to `frame'. The X-axis is given by the cross product of
the Z-axis of `frame' with the direction of the pole of
the central body. The Y-axis completes a right handed
frame.
The specific arrangement of the elements is spelled
out below. The following terms are used in the
discussion of elements of `eqel':
inc --- inclination of the orbit
argp --- argument of periapse
node --- longitude of the ascending node
e --- eccentricity of the orbit
m0 --- mean anomaly
eqel[0] is the semi-major axis (A) of the orbit in km.
eqel[1] is the value of H at the specified epoch:
H = e * sin( argp + node )
eqel[2] is the value of K at the specified epoch:
K = e * cos( argp + node )
eqel[3] is the mean longitude at the epoch of the
elements measured in radians:
( m0 + argp + node )
eqel[4] is the value of P at the specified epoch:
P = tan( inc/1 ) * sin( node )
eqel[5] is the value of Q at the specified epoch:
Q = tan( inc/1 ) * cos( node );
eqel[6] is the rate of the longitude of periapse
at the epoch of the elements.
( dargp/dt + dnode/dt )
This rate is assumed to hold for all time. The
rate is measured in radians per second.
eqel[7] is the derivative of the mean longitude:
( dm0/dt + dargp/dt + dnode/dt )
This rate is assumed to be constant and is
measured in radians/second.
eqel[8] is the rate of the longitude of the ascending
node:
( dnode/dt )
This rate is measured in radians per second.
rapol is the Right Ascension of the pole of the reference
plane relative to `frame' measured in radians.
decpol is the declination of the pole of the reference plane
relative to `frame' measured in radians.
Detailed_OutputNone. The routine writes an SPK type 17 segment to the file attached to `handle'. ParametersNone. Exceptions
1) If the semi-major axis is less than or equal to zero, the
error SPICE(BADSEMIAXIS) is signaled by a routine in the call
tree of this routine.
2) If the eccentricity of the orbit corresponding to the values
of H and K ( eqel[1] and eqel[2] ) is greater than 0.9, the
error SPICE(ECCOUTOFRANGE) is signaled by a routine in the
call tree of this routine.
3) If the segment identifier has more than 40 non-blank
characters, the error SPICE(SEGIDTOOLONG) is signaled by a
routine in the call tree of this routine.
4) If the segment identifier contains non-printing characters,
the error SPICE(NONPRINTABLECHARS) is signaled by a routine in
the call tree of this routine.
5) If there are inconsistencies in the `body', `center', `frame' or
`first' and `last' times, an error is signaled by a routine in
the call tree of this routine.
6) If any of the `frame' or `segid' input string pointers is
null, the error SPICE(NULLPOINTER) is signaled.
7) If any of the `frame' or `segid' input strings has zero
length, the error SPICE(EMPTYSTRING) is signaled.
FilesA new type 17 SPK segment is written to the SPK file attached to `handle'. ParticularsThis routine writes an SPK type 17 data segment to the open SPK file according to the format described in the type 17 section of the SPK Required Reading. The SPK file must have been opened with write access. 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) Suppose that at a given time you have the classical elements
of Daphnis relative to the equatorial frame of Saturn. These
can be converted to equinoctial elements and stored in an SPK
file as a type 17 segment so that Daphnis can be used within
the SPK subsystem of the SPICE system.
The example code shown below creates an SPK type 17 kernel
with a single segment using such data.
Example code begins here.
/.
Program spkw17_ex1
./
#include <math.h>
#include "SpiceUsr.h"
int main( )
{
/.
Local parameters.
./
#define SPK17 "spkw17_ex1.bsp"
/.
The SPK type 17 segment will contain data for Daphnis
(ID 635) with respect to Saturn (ID 699) in the J2000
reference frame.
./
#define BODY 635
#define CENTER 699
#define FRMNAM "J2000"
/.
This is the list of parameters used to represent the
classical elements:
Variable Meaning
-------- ---------------------------------------
A Semi-major axis in km.
ECC Eccentricity of orbit.
INC Inclination of orbit.
NODE Longitude of the ascending node at
epoch.
OMEGA Argument of periapse at epoch.
M Mean anomaly at epoch.
DMDT Mean anomaly rate in radians/second.
DNODE Rate of change of longitude of
ascending node in radians/second.
DOMEGA Rate of change of argument of periapse
in radians/second.
EPOCH The epoch of the elements in seconds
past the J2000 epoch.
./
#define A 1.36505608e+05
#define ECC -2.105898062e-05
#define INC -3.489710429e-05
#define NODE -3.349237456e-02
#define OMEGA 1.52080206722
#define M 1.21177109734
#define DMDT 1.218114014e-04
#define DNODE -5.96845468e-07
#define DOMEGA 1.196601093e-06
#define EPOCH 0.0
/.
In addition, the spkw17_c routine requires the Right
Ascension and Declination of the pole of the
reference plane relative to the J2000 frame, in radians.
./
#define RAPOL 7.08332284e-01
#define DECPOL 1.45800286
/.
Local variables.
./
SpiceChar * ifname;
SpiceChar * segid;
SpiceDouble eqel [9];
SpiceDouble first;
SpiceDouble last;
SpiceInt handle;
SpiceInt ncomch;
/.
Set the start and end times of interval covered by
segment.
./
first = 504878400.0;
last = 1578657600.0;
/.
`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 = "Test for type 17 SPK internal file name";
segid = "SPK type 17 test segment";
/.
Open a new SPK file.
./
spkopn_c ( SPK17, ifname, ncomch, &handle );
/.
Convert the classical elements to equinoctial elements
(in the order compatible with type 17).
./
eqel[0] = A;
eqel[1] = ECC * sin ( OMEGA + NODE );
eqel[2] = ECC * cos ( OMEGA + NODE );
eqel[3] = M + OMEGA + NODE;
eqel[4] = tan( INC/2.0 ) * sin( NODE );
eqel[5] = tan( INC/2.0 ) * cos( NODE );
eqel[6] = DOMEGA + DNODE;
eqel[7] = DMDT + DOMEGA + DNODE;
eqel[8] = DNODE;
/.
Now add the segment.
./
spkw17_c ( handle, BODY, CENTER, FRMNAM, first, last,
segid, EPOCH, eqel, RAPOL, DECPOL );
/.
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 17 exists in
the output directory.
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) Version
-CSPICE Version 1.0.1, 05-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Added complete
code example based on existing example.
-CSPICE Version 1.0.0, 21-JUN-1999 (NJB) (WLT)
Index_EntriesWrite a type 17 SPK segment |
Fri Dec 31 18:41:13 2021